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  1. 1. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 2, February (2014), pp. 110-114, © IAEME 110 EXPERIMENTAL INVESTIGATION OF TENSILE STRENGTH ON AL 6351 TO THE AEROSPACE STRUCTURAL APPLICATIONS M.V. NIRANJAN REDDY1 , M. NIKHIL REDDY2 , K. VIJAY KUMAR3 , PARTHASARATHY GARRE4 1, 2, 3 B.Tech, Aeronautical Dept, MLRIT, Hyderabad, India 4 Assoc Prof, Mechanical Dept, MLRIT, Hyderabad, India ABSTRACT Most of the aerospace structures and its allied infrastructure are made of aluminum alloy. In this context considering Al 6351 which was used for making pressure vessel cylinders is now testing for aircraft structures. Al 6351 has high corrosion resistance and can be seen in forms of extruded rod bar and wire and extruded shapes. It is easily machinable and can have a wide variety of surface finishes. It also has good electrical and thermal conductivities and is highly reflective to heat and light. Due to the superior corrosion resistance, Al 6351 offers extremely low maintenance. Al 6351 is only one-third the weight of cast iron, with about 75% of comparable tensile strength. Early research was done on crack phenomenon of hallow cross sectional specimen only. In this investigation the tensile strength on circular rod specimen of Al 6351 is finding out by applying the loads on universal testing machine with various dimensions. The experimental results were found satisfactory to propose the alternative alloy for aircraft structures. KEYWORDS: Al 6351, AEROSPACE, STRUCTURES, TENSILE STRENGTH, UTM. 1. INTRODUCTION Aluminum alloys are used in many applications in which the combination of high strength and low weight is attractive in air frame in which the low weight can be significant value [1]. Al 6351 is known for its light weight (ρ = 2.7g/cm3) and good corrosion resistance to air, water, oils and many chemicals. Thermal and electrical conductivity is four times greater than steels [2]. The chemical compositions of Al 6351 are Si-0.93, Fe-0.36, Cu-0.1, Mn-0.57, Mg-0.55, Zn-0.134, Ti- 0.014 and remaining Al. It has higher strength amongst the 6000 series alloys. Alloy 6351 is known INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING AND TECHNOLOGY (IJMET) ISSN 0976 – 6340 (Print) ISSN 0976 – 6359 (Online) Volume 5, Issue 2, February (2014), pp. 110-114 © IAEME: www.iaeme.com/ijmet.asp Journal Impact Factor (2014): 3.8231 (Calculated by GISI) www.jifactor.com IJMET © I A E M E
  2. 2. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 2, February (2014), pp. 110-114, © IAEME 111 as a structural alloy, in plate form. This alloy is most commonly used for machining. Though relatively a new alloy the higher strength of 6351 has replaced 6061 alloy in many applications [1]. Mechanical properties can be easily obtained at tension tests, with great accuracy [3]. Thus, alloy such as 6351 have significantly more silicon than magnesium or other elements, but find themselves in the Mg2Si series [4]. The AA 6351 aluminum alloy is used in manufacturing due to its strength, bearing capacity, ease of workability and weldability. It is also used in building boat, column, chimney, rod, mould, pipe, tube, vehicle, bridge, crane and roof. One of the most important properties of AA 6351 aluminum alloy is that the treatment of solid solution is not so critical [5]. One of the major areas of Al 6351 for investigating crack phenomena is the gas cylinders made of this material often prone to crack at various tensile residual stresses [6]. Sustained load cracking, a metallurgical anomaly, occasionally develops in 6351 aluminum alloy high-pressure cylinders. The alloy in use in Australia and other countries was changed from 6351 in T6 temper to 6061 T6 in the early 1990s.Luxfer, a major manufacturer of aluminum cylinders, states that SCUBA cylinders were manufactured from 6351 aluminum alloy during the following periods: Australia, 1975 to 1990; United States, 1972 to mid-1988; and England, 1967 to 1995, and that cylinders manufactured from this alloy are susceptible to cracking in the neck shoulder region. However, Luxfer considers that cylinders manufactured from the 6061 alloy are not susceptible to sustained-load cracks [7]. Al 6351 H 30 series alloy can be used in structural and general engineering items such as rail & road transport vehicles, bridges, cranes, roof trusses, rivets etc with good surface finish. Also it is observed from research that for the wrought aluminum alloy AA6351-T6 show the lowest and most stable strain amplitude [8]. The advantages of Al 6351 have several important performance characteristics that make them very attractive for aircraft structures, namely light unit weight, only one third that of steel, strength comparable to typical other aluminum alloys, excellent corrosion resistance, with negligible corrosion even in the presence of rain and other drastic conditions, high toughness and resistance to low-ductility fracture even at very low temperatures and free of any ductile-to-brittle transition that has sometimes been fatal to older structures and excellent fabricability. These performance characteristics provide significant advantages over conventional aircraft design, fabrication and erection of aerospace structures like light weight and comparable strength enables the use of a higher ratio of live load to dead load, superior corrosion resistance eliminates the need to paint the aluminum components except perhaps for aesthetic purposes resulting in lower maintenance costs, superior low-temperature toughness eliminates concerns about brittle fracture even in the most severe arctic weather, ease of extrusion enables the design of more weight-efficient beam and component cross sections, placing the metal where it is most needed within a structural shape or assembly including providing for interior stiffeners and for joints and the combination of light weight and ease of fabrication. In this paper the experimental investigation was done to provide the confidence that the Al 6351 is not only used for pressure vessels, rail and road bridges but also may be used for aerospace structures. Thus the experimental investigation is provided with the tensile strength and % elongation on UTM. 2. TEST SPECIMEN Standard guidelines are followed for preparing the test specimens of dimensions 12mm and 16mm as shown in the Fig. 1.1.
  3. 3. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 2, February (2014), pp. 110-114, © IAEME 112 Fig 1.1: Test Specimens 3. SELECTION OF MATERIAL Aluminum alloy Al 6351 is a medium Strength alloy with excellent corrosion Resistance. It has the highest strength of the 64430 series alloys. Alloy Al 6351 is known as a structural alloy. The chemical composition of the Al 6351 is given in TABLE 3.1. Table 3.1: Chemical Composition of Al 6351 Si Fe Cu Mn Mg Ti Pb Ca Zr Sn Sb Al 0.8 0.12 0.051 0.52 0.75 0.017 0.012 0.011 0.003 0.004 0.015 97.51 The addition of a large amount of manganese controls the Grain structure which in turn results in a stronger alloy. The mechanical properties of the Al 6351 are listed below in TABLE 3.2. Table 3.2: Mechanical properties of Al 6351 Base Material Al 6351 Density (X1000kg/m3) 2.6-2.8 Elastic Modulus (GPa) 70-80 Tensile Strength (MPa) 250 Strength (MPa) 150 Hardness (HB500) 95 4. EXPERIMENTATION Tensile test has been carried out on Universal Testing Machine on specimens of dimensions 12mm and 16mm as shown in Fig. 4.1 and Fig. 2. Fig 4.1: UTM with 12mm specimen
  4. 4. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 2, February (2014), pp. 110-114, © IAEME 113 Fig 4.2: UTM with 16mm specimen The specimen finally fails after necking which occurs in the specified region. 5. RESULTS AND DISCUSSION The experimental values are tabulated as shown below TABLE 5.1: Table 5.1: Properties after necking Sl No Specimen No Size Cylindrical Shape Ultimate Tensile Strength (MPa) % Elongation 1 1 16mm 231.98 18.23 2 2 16mm 243.79 19.71 3 1 12mm 247.81 18.54 4 2 12mm 245.72 17.96 The specimens after tensile test on UTM are shown below Fig. 5.1 Fig. 5.1: Specimen pieces after tensile test on UTM 6. CONCLUSION In this investigation an attempt was made to identify the tensile strength of the Al 6351 to best suit for the aerospace structures. We can say that this alloy may also be used for the aerospace structures as the production rate is highly available at lowest possible cost due to its earlier manufacture for the pressure vessel cylinders. From this investigation the important conclusions derived are 250MPa tensile strength and 20% elongation of Al 6351 is nearer to the required strength for aerospace structures.
  5. 5. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 2, February (2014), pp. 110-114, © IAEME 114 7. ACKNOWLEDGMENTS The authors would like to express our deep gratitude for all support and guidance for material preparation to Mr. Prasad, Global Metal Solutions, Plot No.316, Miyapur, Hyderabad, Andhra Pradesh, India, Mobile/ Cell Phone: 7396216315, e-mail: saiengineers2008@gmail.com. The authors would also like to thank Mr. Laxminarsayya, Lab Assistant for carrying out this work in Aircraft Structures lab to publish the results. 8. REFERENCE [1]. G. Gopala Krishna, P. Ram Reddy and M. Manzoor Hussain, Experimental Investigation of Tensile Strength and Deflection Characteristics of Friction Stir Welded Aluminum AA 6351 Alloy Joint, IOSR Journal of Mechanical and Civil Engineering, Volume 7, Issue 5, 2013, PP 01-06. [2]. K. Kishore, P.V. Gopal Krishna, K. Veladri and G. Kiran Kumar, Analysis of Defects in Gas Shielded Arc Welding of AA 6351 Using Taguchi Methods, International Journal of Applied Engineering Research, Volume 5 Number 3, 2010, pp. 393–399. [3]. Taylor Mac Intyer Fonseca Junior, Rodrigo Magnabosco, Evaluation of methods for estimating fatigue properties applied to stainless steels and aluminum alloys, Tecnol. Metal. Mater. Miner., Sao Paulo, v. 9, n. 4, 2012, p. 284-293. [4]. J. Gilbert Kaufman, Introduction to Aluminum Alloys and Tempers, ASM International, p23- 37, DOI:10.1361/iaat2000p023. [5]. Hulya Kacar Durmus, Erdogan O zkaya, Cevdet Meri, The use of neural networks for the prediction of wear loss and surface roughness of AA 6351 aluminium alloy, Materials and Design 27, 2006, 156–159. [6]. R N Ibrahim, Y C Lam and D Ischenko, Predictions of residual stresses caused by quenching process in Aluminium 6351- T6 Gas cylinder, International Conference on Fracture, ICF 9- Sydney, Australia- 1997, Volume: 4324/1484. [7]. J.W.H. Price and R.N. Ibrahim, Cracking in Aluminum Gas Cylinders: A Review of Causes and Protection Measures, Practical Failure Analysis, ASM International, PFANF8, Volume 3(6) December 2003, 6:47-55. [8]. Taylor Mac Intyer Fonseca Junior, Rodrigo Magnabosco, Evaluation of methods for estimating fatigue properties applied to stainless steels and aluminum alloys, Tecnologia Metalurgia Materiais e Mineracao, Paulo, v. 9, n. 4, 2012, p. 284-293. [9]. Amir Javidinejad, “Structured Teaching of Machine Design for Future Design Engineers”, International Journal of Mechanical Engineering & Technology (IJMET), Volume 3, Issue 2, 2012, pp. 120 - 127, ISSN Print: 0976 – 6340, ISSN Online: 0976 – 6359. [10]. Parthasarathy Garre, “Branch Height Optimization of Copper Tube Hydroforming using Simulation through Taguchi Technique”, International Journal of Mechanical Engineering & Technology (IJMET), Volume 4, Issue 5, 2013, pp. 250 - 256, ISSN Print: 0976 – 6340, ISSN Online: 0976 – 6359.