1. Pulsed current tungsten inert gas (PCTIG) welding involves cycling the welding current between a high peak level and a low background level at a selected frequency. This allows heat to be applied efficiently in short bursts, limiting heat transfer and producing finer grain structures compared to continuous current welding.
2. An experiment was conducted to determine the optimal parameter ranges for pulsed current TIG welding of AA6061 aluminum alloy. The parameters tested were peak current, background current, pulse frequency, and pulse on-time. Regression analysis was used to develop a model relating these parameters to pitting corrosion potential.
3. Preliminary trials identified peak current between 160-180 amps, background current above
A Comparative Study on Direct and Pulsed Current Gas Tungsten Arc Welding of ...IDES Editor
the aim of this article is to evaluate the mechanical
and microstructure properties of Inconel 617 weldments
produced by direct current electrode negative (DCEN) gas
tungsten arc welding (GTAW) and pulse current GTAW. In
this regard, the micro structural examinations, impact test
and hardness test were performed. The results indicated that
the joints produced by direct mode GTAW exhibit poor
mechanical properties due to presence of coarse grains and
dendrites. Grain refining in pulse current GTAW is reason of
higher toughness and impact energy than DCEN GTAW.
Further investigations showed that the epitaxial growth is
existed in both modes that can strongly affect the mechanical
behavior of the joints in heat affected zone (HAZ).
The document provides guidelines for pre-heat (PH) and post-weld heat treatment (PWHT) of welds during construction activities at sites for boilers and auxiliaries. It specifies requirements for pre-heating temperature based on material thickness and type, methods for pre-heating and PWHT, temperature measurement and control during PWHT using thermocouples. The width of heat treatment band, number and location of thermocouples depends on the component being welded and treated. Proper procedure is to be followed in case of interruptions during any stage of heat treatment.
Welds can fail due to several causes: overload, poor joint design, or bad welding methods. Proper joint design is important to ensure good fusion and avoid defects from rapid heat dissipation. Welding procedures must be qualified to produce acceptable quality welds, and welders must pass approval tests to demonstrate their skills match the approved procedures. Supervision by qualified personnel is also important when carrying out welding operations.
This document provides guidelines for welding duplex and superduplex stainless steels. It discusses joint preparation, preheat and interpass temperature requirements. For root welding, it recommends using TIG with a superduplex filler to ensure corrosion resistance. For filling runs, it describes suitable welding processes like TIG, MMA, MIG, FCAW and SAW. Post weld heat treatment and dissimilar welding combinations are also covered.
Optimization of Weld Bead Parameters of Nickel Based Overlay Deposited by Pla...IJERA Editor
Plasma Transferred Arc surfacing is a kind of Plasma Transferred Arc Welding process. Plasma Transferred Arc surfacing (PTA) is increasingly used in applications where enhancement of wear, corrosion and heat resistance of materials surface is required. The shape of weld bead geometry affected by the PTA Welding process parameters is an indication of the quality of the weld. In this paper the analysis and optimization of weld bead parameters, during deposition of a Nickel based alloy Colmonoy on stainless steel plate by plasma transferred arc surfacing, are made and values of process parameters to produce optimal weld bead geometry are estimated. The experiments are conducted based on a five input process parameters and mathematical models are developed using multiple regression technique. The direct effects of input process parameters on weld bead geometry are discussed using graphs. Finally, optimization of the weld bead parameters, that is minimization of penetration and maximization of reinforcement and weld bead width, are made with a view to economize the input process parameters to achieve the desirable welding joint.
This document outlines welding and inspection requirements for piping systems. It specifies requirements for welding qualification, procedures, personnel qualifications, inspection methods, and acceptance criteria. Welding qualifications must meet the standards of ASME Section IX or EN 288 and include non-destructive testing, mechanical testing of cross-weld tensiles, bends, impacts at required temperatures, macrosections and hardness testing where specified for different material types. Inspection and non-destructive testing of completed welds must be performed according to the standards by qualified personnel and meet the acceptance criteria.
Project presentation on fixture design for eliminating key hole defectSubed Satyal
This project presentation includes the introduction of Friction stir welding along the pipe's circumference and the pipe is made of Aluminum alloy because it is suitable for friction stir welding. It also includes literature review regarding the key hole defect & its elimination. A brief methodology which is adopted for eliminating this defect is also mentioned. The final parts includes introduction, consequences & proposed method to eliminate key hole defect by using sacrificial material. A especially designed fixture is used to clamp the sacrificial material which is manually slides in a cross slide to connect pipe along the weld line with the sacrificial material's curved surface.
Post weld heat treatment (PWHT) is used to reduce or remove residual stresses from welded structures. It involves reheating the weld below the lower transformation temperature at a controlled rate, holding for a specified time, and cooling at a controlled rate. PWHT is required by codes and standards for thicker materials and alloy steels to modify microstructure, temper martensite, and develop creep strength. It generally decreases yield strength and hardness while increasing ductility and toughness. Standards specify techniques, temperatures, heating/cooling rates, and thermocouple requirements for PWHT.
A Comparative Study on Direct and Pulsed Current Gas Tungsten Arc Welding of ...IDES Editor
the aim of this article is to evaluate the mechanical
and microstructure properties of Inconel 617 weldments
produced by direct current electrode negative (DCEN) gas
tungsten arc welding (GTAW) and pulse current GTAW. In
this regard, the micro structural examinations, impact test
and hardness test were performed. The results indicated that
the joints produced by direct mode GTAW exhibit poor
mechanical properties due to presence of coarse grains and
dendrites. Grain refining in pulse current GTAW is reason of
higher toughness and impact energy than DCEN GTAW.
Further investigations showed that the epitaxial growth is
existed in both modes that can strongly affect the mechanical
behavior of the joints in heat affected zone (HAZ).
The document provides guidelines for pre-heat (PH) and post-weld heat treatment (PWHT) of welds during construction activities at sites for boilers and auxiliaries. It specifies requirements for pre-heating temperature based on material thickness and type, methods for pre-heating and PWHT, temperature measurement and control during PWHT using thermocouples. The width of heat treatment band, number and location of thermocouples depends on the component being welded and treated. Proper procedure is to be followed in case of interruptions during any stage of heat treatment.
Welds can fail due to several causes: overload, poor joint design, or bad welding methods. Proper joint design is important to ensure good fusion and avoid defects from rapid heat dissipation. Welding procedures must be qualified to produce acceptable quality welds, and welders must pass approval tests to demonstrate their skills match the approved procedures. Supervision by qualified personnel is also important when carrying out welding operations.
This document provides guidelines for welding duplex and superduplex stainless steels. It discusses joint preparation, preheat and interpass temperature requirements. For root welding, it recommends using TIG with a superduplex filler to ensure corrosion resistance. For filling runs, it describes suitable welding processes like TIG, MMA, MIG, FCAW and SAW. Post weld heat treatment and dissimilar welding combinations are also covered.
Optimization of Weld Bead Parameters of Nickel Based Overlay Deposited by Pla...IJERA Editor
Plasma Transferred Arc surfacing is a kind of Plasma Transferred Arc Welding process. Plasma Transferred Arc surfacing (PTA) is increasingly used in applications where enhancement of wear, corrosion and heat resistance of materials surface is required. The shape of weld bead geometry affected by the PTA Welding process parameters is an indication of the quality of the weld. In this paper the analysis and optimization of weld bead parameters, during deposition of a Nickel based alloy Colmonoy on stainless steel plate by plasma transferred arc surfacing, are made and values of process parameters to produce optimal weld bead geometry are estimated. The experiments are conducted based on a five input process parameters and mathematical models are developed using multiple regression technique. The direct effects of input process parameters on weld bead geometry are discussed using graphs. Finally, optimization of the weld bead parameters, that is minimization of penetration and maximization of reinforcement and weld bead width, are made with a view to economize the input process parameters to achieve the desirable welding joint.
This document outlines welding and inspection requirements for piping systems. It specifies requirements for welding qualification, procedures, personnel qualifications, inspection methods, and acceptance criteria. Welding qualifications must meet the standards of ASME Section IX or EN 288 and include non-destructive testing, mechanical testing of cross-weld tensiles, bends, impacts at required temperatures, macrosections and hardness testing where specified for different material types. Inspection and non-destructive testing of completed welds must be performed according to the standards by qualified personnel and meet the acceptance criteria.
Project presentation on fixture design for eliminating key hole defectSubed Satyal
This project presentation includes the introduction of Friction stir welding along the pipe's circumference and the pipe is made of Aluminum alloy because it is suitable for friction stir welding. It also includes literature review regarding the key hole defect & its elimination. A brief methodology which is adopted for eliminating this defect is also mentioned. The final parts includes introduction, consequences & proposed method to eliminate key hole defect by using sacrificial material. A especially designed fixture is used to clamp the sacrificial material which is manually slides in a cross slide to connect pipe along the weld line with the sacrificial material's curved surface.
Post weld heat treatment (PWHT) is used to reduce or remove residual stresses from welded structures. It involves reheating the weld below the lower transformation temperature at a controlled rate, holding for a specified time, and cooling at a controlled rate. PWHT is required by codes and standards for thicker materials and alloy steels to modify microstructure, temper martensite, and develop creep strength. It generally decreases yield strength and hardness while increasing ductility and toughness. Standards specify techniques, temperatures, heating/cooling rates, and thermocouple requirements for PWHT.
Investigation on effect of welding current on welding speed and hardness of h...eSAT Journals
1) The document investigates the effect of welding current on welding speed and hardness of the heat affected zone (HAZ) and weld metal of mild steel.
2) Testing was conducted on mild steel specimens welded with varying current from 80-100 amps using MMAW. Hardness was measured in the parent metal, HAZ and weld metal.
3) Results showed that as welding current increased, welding time decreased and welding speed increased due to a higher electrode melting rate. Hardness of the HAZ and weld metal decreased with increasing current due to higher heat input.
Research into Properties of Spot Welded Steel Sheetsijtsrd
The contribution deals with parameter optimalization of resistance spot welding for hot dip zinc coated steel sheets. The mechanical properties and metallographic observation of welded joints on galvanized steel sheets were performed. Uncoated sheets from the same material were used for comparison of particular properties. The results showed that welding parameter optimalization is very important for welding of galvanized steel sheets. LuboÅ¡ KaÅ¡c¡k | Denis Cmorej "Research into Properties of Spot Welded Steel Sheets" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-4 | Issue-1 , December 2019, URL: https://www.ijtsrd.com/papers/ijtsrd29773.pdf Paper URL: https://www.ijtsrd.com/engineering/mechanical-engineering/29773/research-into-properties-of-spot-welded-steel-sheets/lubo%C5%A1-ka%C5%A1c%C3%A1k
The document is a dissertation report submitted by Parmod Kumar that examines the behavioural analysis of P22 and P91 steels after TIG welding and post weld heat treatment (PWHT) processes. It includes an introduction to the materials, literature review on welding of P22 and P91 steels, identified research gaps, methodology adopted for the experimental plan, findings from the experiments, results and discussion, and plans for future work. The experimental plan involves TIG welding of P22 and P91 steel samples, analyzing hardness and microstructure after welding, conducting PWHT at varying hold times, and assessing the impact of PWHT on hardness and microstructure.
The effects of heat input and interpass temperature on the microstructure of ...Mark Keeler
This thesis examines the effects of heat input and interpass temperature on the microstructure of duplex stainless steel during welding. Two sets of 5 butt welds were made with heat inputs of 1.0 KJ/mm and 1.5 KJ/mm. The interpass temperature was varied from 150°C to 350°C between welds. Micrographic examination found that intermetallic precipitates formed at a heat input of 1.5 KJ/mm and interpass temperature of 350°C, but not at 1.0 KJ/mm. Lower interpass temperatures of 200°C also showed signs of microstructural effects. The results indicate that excessive heat input and interpass temperatures can alter the microstructure
- Moisture absorption by fluxes during storage is a common problem in submerged arc welding that can reduce flux quality.
- The study investigated recycling moisturized flux by processing it to remove contaminants, drying it in an oven, and mixing it with new flux for reuse.
- Testing of the recycled flux found that its effect on weld metal chemistry was comparable to new flux, allowing the moisturized flux to be effectively reclaimed and reused rather than disposed of.
Investigation on Effect of Heat Input on Cooling Rate and Mechanical Property...IJMER
The effect of heat input in MMAW arc welding on cooling rate and hardness of weld
joint is investigated in this paper. The parameter affects the heat input are welding current, arc voltage
and welding speed. Mild steel weldments were welded under varying current 80, 90 and 100 ampere
and keeping arc voltage and travel speed constant. Other mild steel specimens were welded under
varying arc voltage 21V, 23V and 25V and keeping welding current and welding speed constant. Other
mild steel specimens were welded by varying welding travel speed 1.52 mm/sec, 1.67 mm/sec and 1.82
mm/sec and keeping arc voltage and welding current constant. Heat input was calculated for each
weldment. Rockwell hardness testing of all specimens was done. It was observed that with increase in
arc current hardness of mild steel weld joint was increased up to optimum level and then decreased.
Cooling rate was decreased with increased in arc current. With increase in welding arc voltage
hardness of weld joint decreased and cooling rate was decreased also. With increase in welding travel
speed hardness of weld joint increased and cooling rate was increased also.
The document discusses weld defect acceptance criteria according to different codes such as ASTM B31.1, ASME VIII, ASME B31.3, and AWS D1.1. It provides details on acceptance limits for various weld defects depending on the examination method, material thickness, loading conditions, and material application. Defects discussed include cracks, lack of fusion, incomplete penetration, undercuts, porosity, and reinforcement. Acceptance criteria include maximum defect sizes, numbers of defects allowed, cumulative lengths of defects, and distances between defects.
Feasibility Study for In-Process Monitoring of Gas Tungsten Arc WeldingIJERD Editor
Different methods can be adopted for monitoring the quality and prediction of process stability for Gas Tungsten Arc Welding. The acoustic emissions generated during welding of V groove weld for SS304 material can be utilized to assess the behaviour of weld produced and analyze using softwares. For evaluation of influences of sound generation, extensive experiments have to be performed and a comparative study can be carried out.
The effect of welding heat input and welding speed on microstructure of chrom...eSAT Publishing House
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology
IRJET- Advanced Welding Processes for Distortion Reduction: A ReviewIRJET Journal
This document reviews various advanced welding processes for reducing distortion compared to conventional arc welding processes. It summarizes research comparing the effects of cold metal transfer (CMT) welding, autogenous laser welding, hybrid laser-gas metal arc (GMA) welding, and hybrid laser-magnetic welding on distortion. Studies show these advanced processes generate less heat input and result in lower distortion compared to submerged arc welding and pulsed GMA welding. Specifically, laser welding and laser hybrid welding produce the least amount of angular distortion and transverse displacement. The document concludes advanced welding techniques offer benefits over conventional arc welding in terms of improved weld quality and reduced distortion.
REVIEW ON EFFECT OF HEAT INPUT ON TENSILE STRENGTH OF BUTT WELD JOINT USING M...ijiert bestjournal
This document summarizes a research paper that investigated the effect of heat input on the tensile strength of butt weld joints using MIG welding. The researchers found that increasing heat input affected the microstructure of the base metal and heat affected zone. Tensile strength decreased with higher heat input. Microhardness was observed to increase in the weld pool but decrease in the heat affected zone with greater heat input. Optical microscopy showed smaller dendrite sizes and spacing at low heat input compared to larger dendrites and spacing at high heat input. The extent of grain coarsening in the heat affected zone also increased with higher heat input. In conclusion, welding heat input significantly influences the properties of welded joints.
This document reviews the effects of preheating and post weld heat treatment (PWHT) on hardened steels. It discusses how preheating and PWHT can reduce hardness in the heat affected zone by slowing cooling rates after welding. This decreases residual stresses and susceptibility to cold cracking. The document examines factors that determine necessary preheat temperatures like carbon content and steel thickness. It also provides suggested temperature and duration ranges for PWHT of various hardened steel types to temper martensite and further reduce hardness and stresses.
Post-weld heat treatment (PWHT) is used to improve the properties of welded joints and is often required by codes. The most common PWHT methods are post heating and stress relieving. PWHT aims to reduce residual stresses and improve ductility. It can be performed in fixed or temporary furnaces using direct heating methods. Proper temperature control and rates of heating/cooling must be followed based on material thickness. Thermocouples are used to monitor internal and external temperatures during treatment.
IRJET - Evaluate the Residual Stress Formation of DP600 During RSWIRJET Journal
This study evaluated residual stress formation in DP600 dual phase steel sheets during resistance spot welding (RSW) at different pressures and currents. Samples of DP600 steel were resistance spot welded at pressures of 3.5, 4.5, and 5.5 bar and currents of 4, 6, and 8 kA. Microstructure, hardness, and residual stress of the welded samples were then examined. Results showed that hardness was highest in the weld region due to martensite formation from the high cooling rates of RSW. Hardness increased with higher clamping pressure and current. Residual stress measurements found compressive residual stresses in the specimens, with the highest stresses found in the 5 kA-6 bar samples.
Review on TIG Welding Ang And A-TIG Welding on Aluminum AlloysIRJET Journal
This document summarizes a research paper that studied TIG welding and A-TIG welding of AA5456 aluminum alloys. It investigated the effect of welding parameters on microstructure and mechanical properties. Key findings include:
1) TIG welding with optimized parameters (peak current 80A, base current 40A, speed 230mm/min, frequency 4Hz) produced fine equiaxed grain structure and improved mechanical properties compared to other conditions.
2) A-TIG welding achieved significantly higher weld penetration than conventional TIG welding.
3) Mechanical properties improved by 10-15% after applying post-weld planishing to relieve internal stresses in the weld.
4)
Friction Stir Welding along the circumference of Al pipesSubed Satyal
The document summarizes a presentation on friction stir welding of pipes. It discusses the challenges of experimental procedures for friction stir welding pipes including producing good quality welds and eliminating keyhole defects. It describes the methodology used including using a vertical milling machine with a tapered tool profile. It outlines the welding parameters tested and experimental results including visual inspections showing smooth and rough welds. Microhardness tests showed highest values in the stir zone. Microstructures revealed grain changes in the stir, thermomechanically affected, and heat affected zones. Eliminating the exit hole defect is discussed using a sacrificial element. The conclusion is that taper tool profile produced good quality welds and exit holes can be addressed.
This document provides guidelines for essential variables that determine the qualification range of a welding procedure specification in accordance with AWS D1.1 Structural Welding Code - Steel. It summarizes the qualification ranges for position, thickness/diameter, base metal selection, preheat requirements, joint details, heat input, and welding processes. The guidelines specify the testing parameters and qualified ranges for groove welds, fillet welds, plate and pipe configurations.
Effect of Thickness of Tubes on Pressure of Flare
Original Research Article
Journal of Chemistry and Materials Research Vol. 1 (3), 2014, 52–55
M.T. Hannachi *, B. Dahech, H. Guelouche, M. Fareh
1. Pulsed current tungsten inert gas (PCTIG) welding involves cycling the welding current between a high peak level and a low background level at a selected frequency. This allows precise control of heat input to reduce defects and improve weld properties compared to continuous current welding.
2. An experiment was conducted to determine the feasible parameter ranges for PCTIG welding of AA6061 aluminum alloy. Peak current below 160A or above 180A, and background current below 80A resulted in incomplete penetration, lack of fusion, or an unstable arc.
3. A design of experiments approach was used to develop a mathematical model to predict the pitting corrosion potential of PCTIG welds of AA60
Tungsten inert gas (TIG) welding in which the arc is formed between a pointed tungsten electrode and the work piece in an inert atmosphere of argon or helium but the activated TIG welding is that in which oxides of fluxes are used on work piece also called A-TIG. Current and voltage can have profound effect on the material in terms of strength and hardness. This research aims at the study of using conventional TIG (tungsten inert gas) and activated TIG welding process to investigate the effect of different levels of factors (current, voltage, gas flow rate, electrode diameter) on the mechanical properties of the mild steel using mixture of MgO and CaO flux. Mild steel specimens were used during the experimentation. The results of conventional TIG have been compared with the activated TIG welding. The method of design expert is used to carry out the experimentation. Moreover it is observed that there is decrease in hardness of weld but the quality of weld is increased as compared to conventional TIG welding.
URL: http://ijtir.hctl.org/A-Study-of-Mechanical-Properties-on-Tig-Welding-at-Different-Parameters-with-and-without-use-of-Flux.html
Investigation on effect of welding current on welding speed and hardness of h...eSAT Journals
1) The document investigates the effect of welding current on welding speed and hardness of the heat affected zone (HAZ) and weld metal of mild steel.
2) Testing was conducted on mild steel specimens welded with varying current from 80-100 amps using MMAW. Hardness was measured in the parent metal, HAZ and weld metal.
3) Results showed that as welding current increased, welding time decreased and welding speed increased due to a higher electrode melting rate. Hardness of the HAZ and weld metal decreased with increasing current due to higher heat input.
Research into Properties of Spot Welded Steel Sheetsijtsrd
The contribution deals with parameter optimalization of resistance spot welding for hot dip zinc coated steel sheets. The mechanical properties and metallographic observation of welded joints on galvanized steel sheets were performed. Uncoated sheets from the same material were used for comparison of particular properties. The results showed that welding parameter optimalization is very important for welding of galvanized steel sheets. LuboÅ¡ KaÅ¡c¡k | Denis Cmorej "Research into Properties of Spot Welded Steel Sheets" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-4 | Issue-1 , December 2019, URL: https://www.ijtsrd.com/papers/ijtsrd29773.pdf Paper URL: https://www.ijtsrd.com/engineering/mechanical-engineering/29773/research-into-properties-of-spot-welded-steel-sheets/lubo%C5%A1-ka%C5%A1c%C3%A1k
The document is a dissertation report submitted by Parmod Kumar that examines the behavioural analysis of P22 and P91 steels after TIG welding and post weld heat treatment (PWHT) processes. It includes an introduction to the materials, literature review on welding of P22 and P91 steels, identified research gaps, methodology adopted for the experimental plan, findings from the experiments, results and discussion, and plans for future work. The experimental plan involves TIG welding of P22 and P91 steel samples, analyzing hardness and microstructure after welding, conducting PWHT at varying hold times, and assessing the impact of PWHT on hardness and microstructure.
The effects of heat input and interpass temperature on the microstructure of ...Mark Keeler
This thesis examines the effects of heat input and interpass temperature on the microstructure of duplex stainless steel during welding. Two sets of 5 butt welds were made with heat inputs of 1.0 KJ/mm and 1.5 KJ/mm. The interpass temperature was varied from 150°C to 350°C between welds. Micrographic examination found that intermetallic precipitates formed at a heat input of 1.5 KJ/mm and interpass temperature of 350°C, but not at 1.0 KJ/mm. Lower interpass temperatures of 200°C also showed signs of microstructural effects. The results indicate that excessive heat input and interpass temperatures can alter the microstructure
- Moisture absorption by fluxes during storage is a common problem in submerged arc welding that can reduce flux quality.
- The study investigated recycling moisturized flux by processing it to remove contaminants, drying it in an oven, and mixing it with new flux for reuse.
- Testing of the recycled flux found that its effect on weld metal chemistry was comparable to new flux, allowing the moisturized flux to be effectively reclaimed and reused rather than disposed of.
Investigation on Effect of Heat Input on Cooling Rate and Mechanical Property...IJMER
The effect of heat input in MMAW arc welding on cooling rate and hardness of weld
joint is investigated in this paper. The parameter affects the heat input are welding current, arc voltage
and welding speed. Mild steel weldments were welded under varying current 80, 90 and 100 ampere
and keeping arc voltage and travel speed constant. Other mild steel specimens were welded under
varying arc voltage 21V, 23V and 25V and keeping welding current and welding speed constant. Other
mild steel specimens were welded by varying welding travel speed 1.52 mm/sec, 1.67 mm/sec and 1.82
mm/sec and keeping arc voltage and welding current constant. Heat input was calculated for each
weldment. Rockwell hardness testing of all specimens was done. It was observed that with increase in
arc current hardness of mild steel weld joint was increased up to optimum level and then decreased.
Cooling rate was decreased with increased in arc current. With increase in welding arc voltage
hardness of weld joint decreased and cooling rate was decreased also. With increase in welding travel
speed hardness of weld joint increased and cooling rate was increased also.
The document discusses weld defect acceptance criteria according to different codes such as ASTM B31.1, ASME VIII, ASME B31.3, and AWS D1.1. It provides details on acceptance limits for various weld defects depending on the examination method, material thickness, loading conditions, and material application. Defects discussed include cracks, lack of fusion, incomplete penetration, undercuts, porosity, and reinforcement. Acceptance criteria include maximum defect sizes, numbers of defects allowed, cumulative lengths of defects, and distances between defects.
Feasibility Study for In-Process Monitoring of Gas Tungsten Arc WeldingIJERD Editor
Different methods can be adopted for monitoring the quality and prediction of process stability for Gas Tungsten Arc Welding. The acoustic emissions generated during welding of V groove weld for SS304 material can be utilized to assess the behaviour of weld produced and analyze using softwares. For evaluation of influences of sound generation, extensive experiments have to be performed and a comparative study can be carried out.
The effect of welding heat input and welding speed on microstructure of chrom...eSAT Publishing House
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology
IRJET- Advanced Welding Processes for Distortion Reduction: A ReviewIRJET Journal
This document reviews various advanced welding processes for reducing distortion compared to conventional arc welding processes. It summarizes research comparing the effects of cold metal transfer (CMT) welding, autogenous laser welding, hybrid laser-gas metal arc (GMA) welding, and hybrid laser-magnetic welding on distortion. Studies show these advanced processes generate less heat input and result in lower distortion compared to submerged arc welding and pulsed GMA welding. Specifically, laser welding and laser hybrid welding produce the least amount of angular distortion and transverse displacement. The document concludes advanced welding techniques offer benefits over conventional arc welding in terms of improved weld quality and reduced distortion.
REVIEW ON EFFECT OF HEAT INPUT ON TENSILE STRENGTH OF BUTT WELD JOINT USING M...ijiert bestjournal
This document summarizes a research paper that investigated the effect of heat input on the tensile strength of butt weld joints using MIG welding. The researchers found that increasing heat input affected the microstructure of the base metal and heat affected zone. Tensile strength decreased with higher heat input. Microhardness was observed to increase in the weld pool but decrease in the heat affected zone with greater heat input. Optical microscopy showed smaller dendrite sizes and spacing at low heat input compared to larger dendrites and spacing at high heat input. The extent of grain coarsening in the heat affected zone also increased with higher heat input. In conclusion, welding heat input significantly influences the properties of welded joints.
This document reviews the effects of preheating and post weld heat treatment (PWHT) on hardened steels. It discusses how preheating and PWHT can reduce hardness in the heat affected zone by slowing cooling rates after welding. This decreases residual stresses and susceptibility to cold cracking. The document examines factors that determine necessary preheat temperatures like carbon content and steel thickness. It also provides suggested temperature and duration ranges for PWHT of various hardened steel types to temper martensite and further reduce hardness and stresses.
Post-weld heat treatment (PWHT) is used to improve the properties of welded joints and is often required by codes. The most common PWHT methods are post heating and stress relieving. PWHT aims to reduce residual stresses and improve ductility. It can be performed in fixed or temporary furnaces using direct heating methods. Proper temperature control and rates of heating/cooling must be followed based on material thickness. Thermocouples are used to monitor internal and external temperatures during treatment.
IRJET - Evaluate the Residual Stress Formation of DP600 During RSWIRJET Journal
This study evaluated residual stress formation in DP600 dual phase steel sheets during resistance spot welding (RSW) at different pressures and currents. Samples of DP600 steel were resistance spot welded at pressures of 3.5, 4.5, and 5.5 bar and currents of 4, 6, and 8 kA. Microstructure, hardness, and residual stress of the welded samples were then examined. Results showed that hardness was highest in the weld region due to martensite formation from the high cooling rates of RSW. Hardness increased with higher clamping pressure and current. Residual stress measurements found compressive residual stresses in the specimens, with the highest stresses found in the 5 kA-6 bar samples.
Review on TIG Welding Ang And A-TIG Welding on Aluminum AlloysIRJET Journal
This document summarizes a research paper that studied TIG welding and A-TIG welding of AA5456 aluminum alloys. It investigated the effect of welding parameters on microstructure and mechanical properties. Key findings include:
1) TIG welding with optimized parameters (peak current 80A, base current 40A, speed 230mm/min, frequency 4Hz) produced fine equiaxed grain structure and improved mechanical properties compared to other conditions.
2) A-TIG welding achieved significantly higher weld penetration than conventional TIG welding.
3) Mechanical properties improved by 10-15% after applying post-weld planishing to relieve internal stresses in the weld.
4)
Friction Stir Welding along the circumference of Al pipesSubed Satyal
The document summarizes a presentation on friction stir welding of pipes. It discusses the challenges of experimental procedures for friction stir welding pipes including producing good quality welds and eliminating keyhole defects. It describes the methodology used including using a vertical milling machine with a tapered tool profile. It outlines the welding parameters tested and experimental results including visual inspections showing smooth and rough welds. Microhardness tests showed highest values in the stir zone. Microstructures revealed grain changes in the stir, thermomechanically affected, and heat affected zones. Eliminating the exit hole defect is discussed using a sacrificial element. The conclusion is that taper tool profile produced good quality welds and exit holes can be addressed.
This document provides guidelines for essential variables that determine the qualification range of a welding procedure specification in accordance with AWS D1.1 Structural Welding Code - Steel. It summarizes the qualification ranges for position, thickness/diameter, base metal selection, preheat requirements, joint details, heat input, and welding processes. The guidelines specify the testing parameters and qualified ranges for groove welds, fillet welds, plate and pipe configurations.
Effect of Thickness of Tubes on Pressure of Flare
Original Research Article
Journal of Chemistry and Materials Research Vol. 1 (3), 2014, 52–55
M.T. Hannachi *, B. Dahech, H. Guelouche, M. Fareh
1. Pulsed current tungsten inert gas (PCTIG) welding involves cycling the welding current between a high peak level and a low background level at a selected frequency. This allows precise control of heat input to reduce defects and improve weld properties compared to continuous current welding.
2. An experiment was conducted to determine the feasible parameter ranges for PCTIG welding of AA6061 aluminum alloy. Peak current below 160A or above 180A, and background current below 80A resulted in incomplete penetration, lack of fusion, or an unstable arc.
3. A design of experiments approach was used to develop a mathematical model to predict the pitting corrosion potential of PCTIG welds of AA60
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URL: http://ijtir.hctl.org/A-Study-of-Mechanical-Properties-on-Tig-Welding-at-Different-Parameters-with-and-without-use-of-Flux.html
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At present scenario, INCONEL alloy 625 becomes widely used material in aero industry due to its High
tensile, creep, and rupture strength, outstanding fatigue and thermal-fatigue strength, oxidation resistance, and
excellent weld ability properties. In present work, the plates of 50mm×50mm×3mm are modelled and assembled
for v-butt joint using solid works. This model is imported in the FEA software (ANSYS) to carry out the transient
thermal analysis. The analysis is carried out with different combinations of welding parameters such as voltage,
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A Study on Weld Quality Characteristics of Pulsed Current Micro Plasma Arc We...drboon
Micro Plasma Arc Welding plays a vital role in attaining good weld quality in various engineering applications like bellows, diaphragms etc. The main objective of the present work is to use current pulsing technique while welding SS304L sheets. The paper focuses on studying the influence of various Micro Plasma Arc Welding process parameters like peak current, back current, pulse and pulse width on the weld quality characteristics like weld pool geometry, microstructure, grain size, hardness and tensile properties. The results reveals that the usage of pulsing current, grain refinement has taken place in weld fusion zone, because of which improvement in weld quality characteristics have been observed.
Erosion and Cavitation Tests Applied to Coating Welded with Blends of Stainle...CSCJournals
The process GMAW with its your applications using two wires pointing in the market as an alternative to coating when high productivity is desired. Potential variants emerge from this process as GMAW cold wire and GMAW double wire. One of the biggest difficulty is the setting of its parameters, which in addition to duplicate compared to conventional GMAW, act in a dependent manner. A greater understanding of this technology applied to coatings on turbines in various positions is critical so that you can master the process and its variables, aiming to enhance the application in industry. It was proposed in this study an experimental evaluation to verify the influence of some variables on the profile of cord and wear resistance. For this it is proposed in this paper to make deposits with weld metal AWS 308LSi stainless steel and alloys of cobalt (Stellites 6 and 21) plates in carbon steel SAE 1020 in flat positions. In the characterization of wear in the lining was used the determination of the hardness and surface topography. It is concluded that cobalt alloys have superior resistance to erosive damage with emphasis on the Stellite 21 alloy in erosion and cavitation in Stellite 6. In an intermediate position with respect to wear are mixtures of austenitic stainless steel and cobalt alloys. Therefore, it is essential to study welding processes with multiple wires as proposed in this paper aiming the best combination of alloys for resistance to cavitation-erosion phenomena.
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Study the Effect of Welding Parameters during TIG Welding of Aluminum Plate a...Dr. Amarjeet Singh
Aluminium has very unique properties of light
weight and corrosion resistance and due to this it becomes
very interesting metal in the field of engineering. Mainly this
paper deals with effect and optimization of certain range of
values of process parameters during TIG welding of
aluminium alloy 7075.
In the first cycle of experiment the effect of values
(in wide range) of gas flow rate and welding current during
TIG welding of Aluminium alloy 7075 has been found out on
its mechanical properties such as ultimate tensile strength and
hardness. Visual inspection and dye penetrate test also has
been performed for every sample of welding.
From the results for ultimate tensile strength obtained in first
cycle of experiment, a try has been made to optimize process
parameters in second cycle of experiment by narrowing the
range of values of gas flow rate and welding current. Finally
the near optimal values of gas flow rate and welding current
has been found to get maximum UTS.
IRJET- Carburizing of Plane Carbon Steels by Electrolyte PlasmaIRJET Journal
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1. J. Mater. Sci. Technol., Vol.23 No.2, 2007 223
Effect of Pulsed Current TIG Welding Parameters on Pitting
Corrosion Behaviour of AA6061 Aluminium Alloy
T.Senthil Kumar1) , V.Balasubramanian2)† , M.Y.Sanavullah3) and S.Babu2)
1) Department of Automobile Technology, Bharathidasan University, Tiruchirappalli 620 024, India
2) Department of Manufacturing Engineering, Annamalai University, Annamalainagar 608 002, India
3) Principal, V.M.K.V.Engineering College, Salem 636 308, India
[Manuscript received September 29, 2005, in revised form June 23, 2006]
Medium strength aluminium alloy (Al-Mg-Si alloy) has gathered wide acceptance in the fabrication of light
weight structures requiring a high strength-to weight ratio, such as transportable bridge girders, military
vehicles, road tankers and railway transport systems. The preferred welding process for aluminium alloy is
frequently TIG (tungsten inert gas) welding due to its comparatively easier applicability and better economy.
In the case of single pass TIG welding of thinner section of this alloy, the pulsed current has been found
beneficial due to its advantages over the conventional continuous current process. The use of pulsed current
parameters has been found to improve the mechanical properties of the welds compared to those of continuous
current welds of this alloy due to grain refinement occurring in the fusion zone. A mathematical model has
been developed to predict pitting corrosion potential of pulsed current TIG welded AA6061 aluminium alloy.
Factorial experimental design has been used to optimize the experimental conditions. Analysis of variance
technique has been used to find out the significant pulsed current parameters. Regression analysis has been
used to develop the model. Using the developed model pitting corrosion potential values have been estimated
for different combinations of pulsed current parameters and the results are analyzed in detail.
KEY WORDS: Pulsed current; Tungsten inert gas welding; Medium strength aluminium alloy;
Pitting corrosion; Design of experiments; Analysis of variance
1. Introduction Pulsed current tungsten inert gas (PCTIG) weld-
ing, developed in 1950s, is a variant of TIG welding
Weld fusion zones typically exhibit coarse colum- which involves cycling of the welding current from a
nar grains because of the prevailing thermal condi- high level to a low one at a selected regular frequency.
tions during weld metal solidification. This often re- The high level of the peak current is generally selected
sults in inferior weld mechanical properties and poor to give adequate penetration and bead contour, while
resistance to hot cracking. It is thus highly desirable the low one of the background current is set at a level
to control solidification structure in welds and such a sufficient to maintain a stable arc. This permits arc
control is often very difficult because of higher tem- energy to be used efficiently to fuse a spot of controlled
peratures and higher thermal gradients in welds in dimensions in a short time producing the weld as a se-
relation to castings and the epitaxial nature of the ries of overlapping nuggets and limits the wastage of
growth process. Nevertheless, several methods for re- heat by conducting into the adjacent parent material
fining weld fusion zones have been tried with some in a normal constant current welding. In contrast to
success in the past: inoculation with heterogeneous constant current welding, the fact that the heat en-
nucleants[1] , microcooler additions, surface nucleation ergy required to melt the base material is supplied
induced by gas impingement and introduction of phys- only during peak current pulses for brief intervals of
ical disturbance through torch vibration[2] . time allows the heat to dissipate into the base mate-
rial leading to a narrower heat affected zone (HAZ).
The use of inoculants for refining the weld fusion
The technique has secured a niche for itself in specific
zones is, as a matter of fact, not as successful as in
applications such as in welding of root passes of tubes,
castings because of the extremely high temperature
and in welding thin sheets, where precise control over
involved in welding and also due to the undesirable ef-
penetration and heat input are required to avoid burn
fect of inoculating elements on weld mechanical prop-
through.
erties at the level required for grain refinement. Other
Extensive researches have been performed in this
techniques like surface nucleation and microcooler ad-
process and reported advantages include improved
ditions were also turned down because of the compli-
bead contour, greater tolerance to heat sink varia-
cated welding set-ups and procedures associated with
tions, lower heat input requirements, reduced residual
their use. In this process, two relatively new tech-
stresses and distortion[4] . Metallurgical advantages of
niques, termed as magnetic arc oscillation and cur-
pulsed current welding frequently reported in litera-
rent pulsing, have gained wide popularity because of
ture include refinement of fusion zone grain size and
their striking promise and the relative ease with which
substructure, reduced width of HAZ, control of seg-
these techniques can be applied to actual industrial
regation, etc.[5] . All these factors will help in improv-
situations with only minor modifications of the exist-
ing mechanical properties. Current pulsing has been
ing welding equipment[3] .
used by several investigators to obtain refined grains
in weld fusion zones and improvement in weld me-
† Prof., Ph.D.(IITM), to whom correspondence should be chanical properties[6,7] . However, reported research
addressed, E-mail: visvabalu@yahoo.com.
2. 224 J. Mater. Sci. Technol., Vol.23 No.2, 2007
Table 1 Important factors and their levels
Levels Peak current, P /A Base current, B/A Pulse frequency, F /Hz Pulse on time, T /%
Low (−1) 160 80 2 40
High (+1) 180 90 6 60
alloy to find out the feasible working limits of pulsed
Table 2 Experimental design matrix and test results current TIG welding parameters. AA4043 (Al-5%Si)
Expt No. P B F T ∗
PCP/mV aluminium alloy of 3 mm diameter was used as the
1 −1 −1 −1 −1 −500 filler metal and different combinations of pulsed cur-
2 +1 −1 −1 −1 −475 rent parameters were used to carry out the trial runs.
3 −1 +1 −1 −1 −590 The bead contour, bead appearance and weld quality
4 +1 +1 −1 −1 −540 were inspected to identify the working limits of the
5 −1 −1 +1 −1 −495 welding parameters. From the above analysis, the
6 +1 −1 +1 −1 −460 following observations were made.
7 −1 +1 +1 −1 −535 (1) When peak current was less than 160 A, incom-
8 +1 +1 +1 −1 −510 plete penetration and lack of fusion was observed. At
9 −1 −1 −1 +1 −550 the same time, when peak current was greater than
10 +1 −1 −1 +1 −505 180 A, undercut and spatter was observed on the weld
11 −1 +1 −1 +1 −600 bead surface.
12 +1 +1 −1 +1 −575
(2) When background current is lower than 80 A,
13 −1 −1 +1 +1 −525
the arc length was found to be very short and addi-
14 +1 −1 +1 +1 −490
15 −1 +1 +1 +1 −560 tion of filler metal became inconvenient. On the other
16 +1 +1 +1 +1 −530 hand, when the background current was greater than
Note: ∗ PCP—pitting corrosion potential
90 A, the arc became unstable and arc wandering was
observed due to its increased arc length.
(3) The bead appearance and contours appear to
work on the effect of pulsed current parameters on me- be similar to that of constant current weld beads when
chanical and metallurgical properties are very scant. pulse frequency was less than 2 Hz, while more arc
Moreover, no systematic study has been reported to glare and spatter was experienced if pulse frequency
analyze the influence of pulsed current parameters on was greater than 6 Hz.
mechanical and metallurgical properties. (4) When pulse on time was lower than 40%, the
Thus, in this investigation an attempt was made weld nugget formation was not so smooth due to in-
to develop a mathematical model to predict the effect complete melting of filler metal. On the contrary,
of pulsed current TIG welding parameters on pitting when the pulse on time was greater than 60%, the
corrosion behaviour of medium strength AA6061 alu- overmelting of filler metal and overheating of tung-
minium alloy using statistical tools such as design of sten electrode was noticed.
experiments, analysis of variance and regression anal-
ysis. 2.3 Developing the experimental design matrix
By considering all the above conditions, the fea-
2. Scheme of Investigation sible limits of the parameters have been chosen such
that the AA6061 aluminium alloy should be welded
In order to achieve the desired aim, the present in- without any weld defects. Due to narrow ranges of
vestigation was planned in the following sequence: (1) factors, we decided to use two level, full factorial de-
identifying the important pulsed current TIG welding sign matrix to optimize the experimental conditions.
parameters, which have influence on grain refinement Table 1 presents the ranges of factors considered and
in fusion zone and corrosion resistance; (2) finding the Table 2 shows the 16 sets of coded conditions used to
upper and lower limits of the identified parameters; form the design matrix, 24 (2 levels and 4 factors) fac-
(3) developing the experimental design matrix; (4) torial design. The 16 experimental conditions (rows)
conducting the experiments according to the design have been formed for main effects by using the for-
matrix; (5) recording the responses; (6) developing mula 2nc−1 for the low (−1) and high (+1) values;
mathematical models; (7) identifying the significant where ‘nc’ refers to the column number. For exam-
factors; (8) checking the adequacy of the developed ple, in Table 2, the first four rows are coded as −1 and
models. next four rows are coded as +1, alternatively, in the
third column (because nc=3 and therefore 23−1 =4).
2.1 Identifying the important parameters The method of designing such a matrix can be found
From the literature[5–8] and our previous work[9] , in literature[10,11] .
the predominant factors which have greater influence For the convenience of recording and processing
on fusion zone grain refinement of pulsed current TIG the experimental data, upper and lower levels of the
welding process have been identified. They include: factors have been coded as +1 and −1, respectively,
(1) peak current; (2) background current; (3) pulse and the coded values of any intermediate levels can
frequency and (4) pulse on time. be calculated using the following expression[12] .
Xi = X − [(Xmax + Xmin )/2]/[(Xmax − Xmin )/2] (1)
2.2 Finding the working limits of the parameters
A large number of trial runs were carried out us- where Xi is the required coded value of a factor for
ing 5 mm thick rolled plates of AA6061 aluminium any value X from Xmin to Xmax ; Xmin is the lower
3. J. Mater. Sci. Technol., Vol.23 No.2, 2007 225
Table 3(a) Chemical composition (wt pct) of base metal and all weld metal
Type of material Mg Mn Fe Si Cu Al
Base metal (AA6061) 0.689 0.331 0.230 0.531 0.305 Bal
All weld metal (AA4043) 0.050 0.220 0.050 5.0 0.120 Bal
Table 3(b) Mechanical properties of base metal and all weld metal
Type of material Yield strength Ultimate tensile strength Elongation Vickers hardness, 0.05 kg
/MPa /MPa /(%)
Base metal (AA6061) 270 310 10 240
All weld metal (AA4043) 140 210 7 260
level of the factor and Xmax is the upper level of the where b0 is the average of responses (pitting corrosion
factor. potential); b1 , b2 , b3 ,......b15 are the coefficients that
depend on respective main and interaction factors and
2.4 Conducting the experiments and recording the re-
can be calculated by following expression[10] .
sponses
The base metal used in this investigation is a bi = Σ(Xi · Yi )/n (4)
medium strength aluminium alloy of AA6061 grade.
The chemical composition of the base metal was ob- where ‘i’ varies from 1 to n, in which Xi is the cor-
responding coded value of a factor and Yi is the cor-
tained using a vacuum spectrometer (ARL-Model:
responding response output value (pitting corrosion
3460). Sparks were ignited at various locations of the
potential) obtained from the experiment and ‘n’ is
base metal sample and their spectrum was analyzed
the total number of combinations considered (in this
for estimation of the alloying elements. The chemi-
case n=16).
cal composition of the base metal in weight percent is
Analysis of variance (ANOVA) method was ap-
given in Table 3. The polarization test was carried out
plied to find out the significance of main factors and
in non-deaerated 3.5% NaCl solution of pH 7. Analar
interaction factors. The higher order interactions (3
grade chemicals and double distilled water were used
and 4 factor interactions) are practically insignificant
for preparation of the electrolyte. The specimens were
prepared according to the metallographic standard. and hence not considered[13] . Yate s algorithm was
Specimens of 20 mm×40 mm (width and length) were used to calculate the sum of squares. Table 4 repre-
prepared to ensure the exposure of 10 mm diameter sents the Yate s algorithm and in the column marked
circular area in the weld region to the electrolyte. The (1), the upper half was obtained by adding successive
rest of the area was covered with an acid resistant lac- pairs of treatments and the lower half by subtracting
quer. A potentiostat (Gill AC) was used for this study successive pairs. Columns (2), (3) and (4) were ob-
in conjunction with an ASTM standard cell and per- tained in the same manner from the entries in columns
sonal computer. The corrosion rate was calculated by (1), (2) and (3), respectively. Each sum of square was
polarizing the specimen anodically and cathodically obtained by squaring the corresponding effect total
and by extrapolating the Tafel regions of anodic and and dividing the result by r. 2nf , where ‘r’ is number
cathodic curves to the corrosion potential. The inter- of replicates (trials) and ‘nf ’ is the number of chosen
section of these two lines at the corrosion potential factors. Further details regarding ANOVA method
yields the corrosion current density, icorr . The corro- and Yate s algorithm can be found in literature[10,11] .
sion potential and corrosion current density were ob-
tained for each Tafel plot directly from the personal 3.1 Final mathematical model
computer attached to the polarization set-up. ANOVA test results are presented in Table 5.
From the ANOVA test results, it is evident that all
3. Mathematical Model the main factors (P, B, F, T ) and few interaction fac-
tors (BF and BT ) were considered to be significant.
In order to represent the PCP of the joint, the Hence the final model was developed including only
response function can be expressed as follows[10–12] . these significant factors and given below.
PCP = f (peak current (P ), base current (B ), (PCP) = {(−528) + 16.88(P ) − 27.5(B ) +
pulse frequency (F ), pulse on time (T ))
PCP = f (P , B , F , T ) (2)
14.38(F ) − 4.38(T ) + 6.88(BF ) − 3.13(BT )}mV
The model selected includes the effects of main (5)
factors and first order interaction of all factors. It
is a portion of power series polynomial expressed as 3.2 Checking adequacy of the developed model
follows. Coefficient of correlation ‘r’ is used to find how
close the predicted and experimental values lie and it
PCP = b0 + b1 (P ) + b2 (B) + b3 (F ) + b4 (T ) + b5 (P B)+ is calculated using the following expression.
b6 (P F ) + b7 (P T ) + b8 (BF ) + b9 (BT )+ r 2 = Explained variation/Total variation =
b10 (F T ) + b11 (P BF ) + b12 (P BT ) +
¯ ¯
Σ(PCPp − PCP)2 /Σ(PCPe − PCP)2 (6)
b13 (P F T ) + b14 (BF T ) + b15 (P BF T ) (3)
4. 226 J. Mater. Sci. Technol., Vol.23 No.2, 2007
Table 4 Yate s algorithm to calculate sum of squares for pitting corrosion potential (PCP)
Y [1] [2] [3] [4] SS
−500 −975 −2105 −4105 −8440 4E+06 1
−475 −1130 −2000 −4335 270 4556.3 P
−590 −955 −2230 135 −440 12100 B
[+] −540 −1045 −2105 135 −10 6.25 PB
−495 −1055 75 −245 230 3306.3 F
−460 −1175 60 −195 −20 25 PF
−535 −1015 70 15 110 756.25 BF
−510 −1090 65 −25 −20 25 P BF
−550 25 −155 105 −230 3306.3 T
−505 50 −90 125 0 0 PT
−600 35 −120 −15 50 156.25 BT
[−] −575 25 −75 −5 −40 100 P BT
−525 45 25 65 20 25 FT
−490 25 −10 45 10 6.25 PFT
−560 35 −20 −35 −20 25 BF T
−530 30 −5 15 50 156.25 P BF T
Table 5 ANOVA (analysis of variance) test results for pitting corrosion potential
Factors
Sum of squares (SS) Degrees of freedom (d.o.f.) Mean squares (SS/d.o.f.) Fratio (MS/error)
Main factors
P 4556.25 1 4556.25 72.9
B 12100 1 12100 193.6
F 3306.25 1 3306.25 52.9
T 3306.25 1 3306.25 52.9
Two factors
∗
PB 6.25 1 6.25 0.1
∗
PF 25 1 25 0.4
∗
PT 0 1 0 0
BF 756.25 1 756.25 12.1
∗
BT 156.25 1 156.25 2.5
∗
FT 25 1 25 0.4
Error 312.5 5 62.5 –
Total 24550 15 – –
Note: ∗ F(1,5,0.95) =6.41. Therefore, P B, P F , P T , BT & F T are not significant at 95% confidence level
where PCPp is predicted (using the above model) pit- stresses built up during freezing exceed the strength of
ting corrosion potential value for the given factors; the solidifying weld metal. The commonly used meth-
PCPe is the experimental value for the correspond- ods to reduce the tendency for solidification cracking
¯
ing factors; PCP is the average of experimental pit- include: altering weld metal composition, through the
ting corrosion potential values. The value of ‘r’ for addition of a filler wire, close process control, and con-
the above developed model is found to be 0.92, which trolling the grain structure within the fusion zone. It
indicates high correlation between experimental and is widely accepted that by changing the weld s grain
predicted values. structure, from coarse columar to fine equiaxed, bet-
ter cohesion strength can be obtained, and the re-
4. Discussion maining eutectic liquid present during the final stage
of solidification can be fed more easily and the pre-
The mathematical model developed in the above formed cracks may be healed[14,15] .
section has been written in C program and the devel- Another way of reducing the susceptibility to so-
oped C program has been used to estimate the pitting lidification cracking is through fusion zone grain re-
corrosion potential of the pulsed current TIG welded finement, which confers the further benefit that the
AA6061 aluminium alloy welds for different combi- weld metal mechanical properties are improved. Var-
nations of pulsed current parameters. Predicted val- ious grain refinement techniques have been discussed
ues were plotted and displayed in Fig.1. The plotted in the literature for aluminium alloy welds, e.g. elec-
graphs can be effectively used to understand the ef- tromagnetic stirring, current pulsing, torch vibration
fect of pulsed current parameter, such as peak current, and inoculation. Of these, pulsed current welding
base current, pulse frequency and pulse on time, on technique has gained wide popularity because of their
pitting corrosion resistance of TIG welded AA6061 striking promise and the relative ease with which
aluminium alloy joints. Figure 2 reveals the fusion these techniques can be applied to actual industrial
zone microstructure of the welded joints. situations with only minor modifications to the exist-
ing welding equipment[17] .
4.1 Effect of pulsed current parameters on fusion zone In general, the formation of equiaxed grain struc-
grain size ture in CCTIG (continous current tungsten inert gas)
Solidification cracking occurs when the thermal weld is known to be difficult because of the remelting
5. J. Mater. Sci. Technol., Vol.23 No.2, 2007 227
Fig.1 Effect of pulsed current parameters on pitting corrosion potential
of heterogeneous nuclei or growth centers ahead of the up may not be effective in welding because of the
solid-liquid interface. This is due to the high tem- small size of the fusion welds and the fine interden-
perature in the liquid, thus making survival nuclei drite spacing in the weld microstructure. Thus grain
difficult. The microstructural evolution in weld fu- refinement observed in the PCTIG welds is therefore
sion zone is also influenced in many ways by current believed to be due to other effects of pulsing on the
pulsing, principally, the cyclic variations of energy in- weld pool shape, fluid flow and temperature. The con-
put into the weld pool cause thermal fluctuations, one tinual change in the weld pool shape is particularly
consequence of which is the periodic interruption in important. As the direction of maximum thermal
the solidification process. As the pulse peak current gradient at the solid-liquid interface changes contin-
decays the solid-liquid interface advances towards the uously, newer grains successively become favourably
arc and increasingly becomes vulnerable to any distur- oriented. Thus, while each grain grows only a small
bances in the arc form. As current increases again in distance, more grains grow resulting in a fine-grained
the subsequent pulse, growth is arrested and remelt- structure[14] .
ing of the growing dendrites can also occur. Current The weld pool solidification during fusion welding
pulsing also results in periodic variations in the arc begins with the epitaxial growth of grains from par-
forces and hence an additional fluid flows that low- tially melted zone grains along the fusion boundary,
ers temperatures in front of the solidifying interface. at the interface between the base metal and fusion
Furthermore, the temperature fluctuations inherent zone. The partially melted grains provide excellent
in pulsed welding lead to a continual change in the sites for growth with the growth rate exceeding the
weld pool size and shape favoring the growth of new nucleation rate in this region. Epitaxial growth across
grains. It is also noted that effective heat input for the weld pool results in long and oriented columnar
unit volume of the weld pool would be considerably grains. The epitaxial grains are the final result of
less in pulse current welds, so the average weld pool continuing growth of the partially melted grains from
temperatures are expected to be low[16,17] . the fusion boundary. Epitaxial growth requires that a
It is important to note that while dendrite frag- minimal degree of undercooling prevail. In contrast,
mentation has frequently been cited as a possible the nucleation of new grains both at and near the fu-
mechanism, evidence for this has not been found. It sion boundary necessitates a free energy barrier to be
was suggested that the mechanism of dendrite break- overcome. Consequently, no undercooling is necessary
6. 228 J. Mater. Sci. Technol., Vol.23 No.2, 2007
Fig.2 Micrographs of fusion zone region: (a) Joint 1 (D=40 µm), (b) Joint 2 (D=30 µm), (c) Joint 3 (D=65 µm),
(d) Joint 4 (D=55 µm), (e) Joint 5 (D=35 µm), (f) Joint 6 (D=20 µm), (g) Joint 7 (D=50 µm), (h) Joint
8 (D=40 µm), (i) Joint 9 (D=55 µm), (j) Joint 10 (D=35 µm), (k) Joint 11 (D=75 µm), (l) Joint 12
(D=60 µm), (m) Joint 13 (D=50 µm), (n) Joint 14 (D=30 µm), (o) Joint 15 (D=60 µm ), (p) Joint 16
(D=45 µm)
for nucleation. To initiate nucleation in the weld de- metallics are the initiation sites for pitting in Al-Zn-
posit and concurrently promote epitaxial grain refine- Mg-Cu alloys. The pitting is due to local dissolution
ment, it is essential to either increase the driving force, of the matrix or to dissolution of the intermetallics be-
i.e. degree of undercooling, or reduce the free energy cause there is galvanic coupling between intermetallics
barrier by introducing trace amounts of zirconium or and matrix. The intermetallics containing Cu and Fe
titanium to the aluminium weld pool[18] . are cathodic with respect to matrix and promote dis-
solution of the matrix, while Mg-rich intermetallics
4.2 Effect of pulsed current parameters on pitting are anodic with respect to the matrix and dissolve
corrosion preferentially[21,22] . In general, the pitting corrosion
The microstructure of AA6061 exhibits inter- resistance of AA6061 aluminium welds was found to
metallics and strengthening particles. The inter- be lower than that of the base metal. This can be at-
metallics are formed during casting and ingot homoge- tributed to the presence of segregation products in as
nization due to interaction between alloying elements solidified welds. The poorest corrosion resistance ex-
and impurities present in the alloy. In AA6061 the hibited by continuous current welds can be attributed
Mg2 Si intermetallics undergo phase transformation to the presence of continuous network of grain bound-
and change their morphology during ingot homoge- ary precipitates mainly containing magnesium rich η
nization, but they are not affected by solution heat phase. Region adjacent to the grain boundary is ex-
treatment and aging of the alloy. The strengthen- pected to be depleted in magnesium due to the pres-
ing particles have composition Mg2 Si and size in the ence of magnesium rich η at grain boundaries. These
nanometer range. Their precipitation in the matrix areas containing lower amounts of magnesium are the
during aging provides strength to the alloy. In ad- preferred locations for corrosion.
dition, the strengthening particles precipitate at the A relatively more uniform distribution of pits was
grain boundaries strongly affecting the resistance of observed in pulsed current welds and this is due to
intergranular corrosion of the alloy[19,20] . the absence of a continuous grain boundary precip-
However, Al7 Cu2 Fe and (Al,Cu)6 (Fe,Cu) inter- itates and to lower microsegregation of silicon and
7. J. Mater. Sci. Technol., Vol.23 No.2, 2007 229
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