Successfully reported this slideshow.
We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads. You can change your ad preferences anytime.
SIMTech technical reports (STR_V11_N1_01_FTG)                                    Volume 11 Number 1 Jan-Mar 2010          ...
A. E. W. Jarfors et al     Uniaxial tensile test of the specimens were per-                                               ...
High temperature formability in AA5083 and AA6061                               0.5                                       ...
A. E. W. Jarfors et al     It is found that less grain growth and weakerstrain hardening could happen in specified testing...
High temperature formability in AA5083 and AA6061     The MRO business in Singapore could also                [5] Y. Wu, L...
Upcoming SlideShare
Loading in …5
×

!!!!!!!!!!!!!!!High temperature formability in aa5083 and aa6061

942 views

Published on

Published in: Business, Technology
  • Be the first to comment

  • Be the first to like this

!!!!!!!!!!!!!!!High temperature formability in aa5083 and aa6061

  1. 1. SIMTech technical reports (STR_V11_N1_01_FTG) Volume 11 Number 1 Jan-Mar 2010 High temperature formability in AA5083 and AA6061 A. E. W. Jarfors, Y. Aue-U-Lan, S. Castagne, J. Liu1, and M. J. Tan1Abstract – In this paper, considering the limited AA5083 and AA6061 were investigated during highapplications in non-superplastic materials, two typical temperature tensile tests to study their formability.alloys of AA5083 and AA6061 were investigated and The results of the tensile test coupled with opticalcompared during high temperature tensile tests to microscopy have been investigated, which indicatestudy their formability. The results of tensile tests and the deformation properties under different test condi-microscopy are shown which indicate the deformation tions. The flow stress as a function of temperature andproperties under different test conditions. It is found strain rate has been shown to establish the formabilitythat the flow stress coupled with the dynamic grain of these two alloys. Furthermore, the highest straingrowth is related with the temperatures and strain rate sensitivity (m-value) is obtained, which wouldrates. Furthermore, the highest strain rate sensitivity verify the feasibility of being used in a new concept(m value) is obtained. Hence, the results would be SPF.analysed so as to apply those non-superplastic mate-rials for a new concept superplastic forming. 3 EXPERIMENTAL The rolled AA5083 and AA6061 sheets withKeywords: Aluminum alloy, Superplastic & non- thickness of 3 mm were used for high temperaturesuperplastic forming, Flow stress, Strain rate sensi- tensile test and microstructure observation. Tensiletivity, Elongation specimens with 20 mm gauge lengths and 4 mm gauge widths were machined from the sheets. In order to obtain better formability during test, all the AA50831 BACKGROUND and AA6061 specimens have been annealed for 2 hours at the temperatures of 345ºC and 415ºC, re- Generically, the aluminum alloys of spectively. For AA5083, an aging treatment at 150ºCheat-treatable and high strength are common used for 24 hours was proved to be helpful to successfullymaterials, such as 7075, 7475, 2024, 5083 and 6061 reveal the microstructure by decorating the grain[1]. Superplastic materials are polycrystalline solids boundary with precipitates. The samples were thenwhich have the ability to undergo large uniform mechanically polished and etched with Graf Sergeantstrains prior to failure [2]. etchant (15.5 mL HNO3, 0.5 mL HF, 3 g Cr2O3, and As a commercial alloy with corrosion resistance 84 mL H2O) [3].and moderate to high strength, the 5083 aluminum Figure 1 shows the typical optical microstructurealloy is widely used in structural sheet-metal applica- of AA5083 in the annealed condition. The grains weretions [3]. somewhat brick shaped rather than equiaxed. The In order to obtain great formability and me- grain size was measure by the linear intercept methodchanical properties, the materials with superplasticity [6]. It is about 13.6 µm in average.should be specially prepared. A lot of processingapproaches including rolling, forging, extrusion,ECAE, FSP and various techniques have been used toproduce fine recrystallised grain size and the obser-vation of superplasticity [4-7]. However, thosethermo-mechanical processing methods would limitthe Superplastic Form (SPF) to great development dueto relatively higher time and cost consuming [8].Based on the limitations, a more formable materialcontaining fine and stable structure but low cost is ofgreat need, or move forward with the process devel-opment by expanding the conventional materials to beused as the SPF application.2 OBJECTIVE In this paper, considering the limited applications Fig. 1. Micrographs of AA5083 in the annealed condition.in non-superplastic materials, two typical alloys of1 School of Mechanical & Aerospace Engineering, Nanyang Technological University, Singapore 1
  2. 2. A. E. W. Jarfors et al Uniaxial tensile test of the specimens were per- The true stresses as a function of strain rate atformed using Instron 8500 testing machine equipped different temperatures are plotted in Fig. 3. For bothwith an electrical resistance furnace chamber. The materials, it can be found that the curves show typicalspecimens were tested in the temperature range of sigmoidal profiles. The flow stress appears to be300ºC, 400ºC and 500ºC at constant crosshead dis- somewhat related with the strain rate, while it increaseplacement velocity, with the corresponding initial with increasing strain rate. Besides, the two materialsstrain rate from 0.0003s-1 to 0.3s-1. vary very much from each other especially during higher strain rates.4 RESULTS & DISCUSSION The strain rate sensitivity (m value), calculated from slopes of the log stress versus log strain rate,4.1 High Temperature Tensile Tests ( m = d log σ / d log ε ), are plotted in Fig. 4 respec- & Figure 2 shows the true stress-strain plots for a tively. The main trends for data on m value are asseries of initial strain rates at temperature of 300ºC. It follows:can be observed from Fig. 1, for both materials, the (1) Generally, the m values peaks increase as theflow stress appears to increase with decreasing strain temperature increasing except AA5083. As resultrate. It has been reported that the enhanced strain of weak strain hardening and grain growth effectshardening at slower strain rates may because of dy- during testing at 300ºC, the alloy behaves highnamic grain growth. However, the curves exhibit stress at higher strain rate but low stress at lowerrelatively weaker strain hardening effects especially at strain rate.strain rates lower than 0.1s-1. Furthermore, it shows (2) For superplastic behaviour, m value would belower strain hardening during constant speed tests greater than or equal to 0.3 [1,2]. However, thiscompared with the corresponding constant strain rate would not happen because of the non-superplastictests [3]. The curves show the similar profiles at dif- materials. Unlike the superplastic materials, bothferent initial stain rates under higher temperature of AA5083 and AA6061 show the maximum vales400ºC or 500ºC. at higher strain rate. A maximum value of 0.41 is obtained at 300ºC for AA5083, while 0.24 for AA6061 at 500ºC. 200 (a) AA5083 3E-1 1000 o 160 1E-1 (a) AA5083 300 C 2E-2 o 400 C 1E-2 True stress, MPa o 1E-3 400 C 120 1E-4 Flow stress, MPa 100 80 40 0 10 0.0 0.1 0.2 0.3 0.4 0.5 0.6 -4 -3 -2 -1 0 True strain 10 10 10 10 10 -1 Strain rate, s (a) AA5083 (a) AA5083 100 (b) AA6061 1000 o (a) AA5083 300 C 3E-1 o 400 C 80 1E-1 o 2E-2 400 C 1E-2 True stress, MPa Flow stress, MPa 1E-3 60 100 40 20 10 0 10 -4 10 -3 10 -2 10 -1 10 0 0.0 0.1 0.2 0.3 0.4 0.5 -1 Strain rate, s True strain (b) AA6061 (b) AA6061Fig. 2. True stress-true strain tensile tests curves at 300ºC Fig. 3. Strain rate dependence of flow stress at differentand various initial strain rates. temperatures. 2
  3. 3. High temperature formability in AA5083 and AA6061 0.5 o (a) AA5083 300 C o 400 C 120 o o (b) AA6061 300 C 0.4 500 C o 400 C 100 o 500 C 0.3 m value Elongation, % 80 0.2 60 0.1 40 0.0 -4 -3 -2 -1 0 20 Logarithm of strain rate -3 -2 -1 0 10 10 10 10 (a) AA5083 -1 Initial strain rate, s 0.5 o (b) AA6061 300 C o 400 C (b) AA6061 o 0.4 500 C Fig. 5. Tensile elongation as a function of initial strain rate 0.3 at different temperatures. m value 0.2 It is true that there would be much more cavities and grain growth at 500ºC. The largest elongations are 0.1 93.25% and 69.00% respectively for AA5083 and AA6061 at 500ºC. Besides, the m value confers a high 0.0 resistance to neck development and results in the high -3 -2 -1 0 tensile elongations [2], so that the maximum elonga- Logarithm of strain rate tion is coincide with the ranges of highest m value (b) AA6061 distributions.Fig. 4. The m values plotted as a function of log strain rate at 4.2 Microstructuredifferent temperatures. Typical micrographs of AA5083 tested at 300ºC and initial strain rate of 10-4s-1 in the grip and gauge The total elongation of test samples is used as a regions are shown in Fig. 6. Not surprisingly, themeasure of the formability of the material, and is grains appear to be somewhat coarser in the samplestypically a function of strain rate and temperature. The deformed due to the grain growth at high temperature.elongation for both alloys is plotted as a function of The increase in-grain growth caused by differentlog initial strain rate and is shown in Fig. 5. Generally, temperature is evident by comparing the microstruc-the tensile elongation increases with increasing strain ture with Fig. 7. Similarly to the superplastic materialsrate and test temperature. This trend is different from [10], the alloy shows much more grain growth atthe superplastic materials with slower strain rate 500ºC. The average grain size of grip region is aboutshowing larger elongations [7,9-11]. However, the 22.5 µm at 300ºC, while some of the grains grow aselongations do not vary a great from different rates high as 200 µm at 500ºC. The microstructure alsoduring test at 300ºC or 400ºC. That is probably due to contains a wide range of grain sizes, which are com-the relatively less cavitation and weaker strain hard- posed of the new, smaller grains formed due to re-ening effects especially at high rate. crystallisation. It is interesting to note that the grains have higher aspect ratio along the tensile direction at 120 (a) AA5083 300 C o 300ºC. o 400 C It has been reported that the failure is mostly in- o 100 500 C ternal cavitation at the lower strain rates; but it changes to external necking at higher rates [10]. As a Elongation, % 80 result, there are more cavities with the decreasing of 60 strain rate. Furthermore, there are much more cavities and grain growth at higher temperature of 500ºC. The 40 fracture tips have jagged appearance especially at lower rates. That is most likely because the sample 20 fractures along the intergranular cavities. -4 -3 -2 -1 0 10 10 10 10 10 -1 Initial strain rate, s (a) AA5083 3
  4. 4. A. E. W. Jarfors et al It is found that less grain growth and weakerstrain hardening could happen in specified testingcondition. Besides, the dislocation creep seems play arole during deformation [11]. Although neither of thetwo non-superplastic materials can behave as high asthe elongation of superplasticty, the relative low flowstress, ductility, microstructure, temperature andstrain rate would be considered for the formabilitybehaviour. Hence, a new approach could be appliedby using those non-superplastic materials for a newconcept superplastic forming. (b) Gauge region Fig. 7. Micrographs of AA5083 tested at 500ºC and initial strain rate of 10-4s-1. 5 CONCLUSIONS AA5083 and AA6061 specimens have been an- nealed for testing the formability at high temperature and different rates. The mechanical properties cou- pled with microstructure have indicated the formabil- ity behaviour. Experimental results also prove the (a) Grip region capability of applying those non-superplastic materi- als for a new concept superplastic forming. The con- clusions are summarised as follows: 1. Both of the two alloys exhibit relatively weaker strain hardening effects especially at relatively lower strain rates. Generally, the flow stress in- creases with increasing strain rate. 2. The m peaks increase as the temperature in- creasing, except AA5083 at 300ºC. Both AA5083 and AA6061 show the maximum values at higher strain rate. A maximum m value of 0.41 is ob- tained at 300ºC for AA5083, while 0.24 for AA6061 at 500ºC. 3. The largest elongations are 93.25% and 69.00% respectively for AA5083 and AA6061 at 500ºC. The elongation is also coinciding with the ranges (b) Gauge region of highest m value distributions.Fig. 6. Micrographs of AA5083 tested at 300ºC and initial 4. The grains appear to be somewhat coarser in thestrain rate of 10-4s-1. samples deformed due to the grain growth at high temperature. The grain size is about 13.6 µm in annealed condition, while it grows up to 22.5 µm at 300ºC and as high as 200 µm at 500ºC. 5. Recrystallisation happens during deformation. There are more cavities at higher temperature and lower strain rate. The sample fractures along the intergranular cavities. 6 INDUSTRIAL SIGNIFICANCE The assesment of the material properties at extreme tyemperature has significance tot hew tool design when forming these traditionally non- superplastic materials. Superplastic forming is now entering Singapore with the new investment in jet engine manufacturing and as such the process is (a) Grip region gaining in importance. 4
  5. 5. High temperature formability in AA5083 and AA6061 The MRO business in Singapore could also [5] Y. Wu, L.D. Castillo, and E.J. Lavernia, “Superplasticventure into high mix low volume manufacturing Behavior of Spray-Deposited 5083 Al”, Metallurgicalusing superplastic forming using the cost advantage Mater. Transac. A, vol. 28A, pp. 1059-1068, 1997.iof the non-superplastic grades of materials for legacy [6] D.H. Bae, and A.K. Ghosh, “Grain Size and Tem- perature Dependence of Superplastic Deformation inparts for the aircraft nmanufacturer to strengthen the an Al-Mg Alloy Under Isostructural Condition”, Actaposition as a total MRO hub. Materialia, vol. 48, pp. 1207-1224, 2000. The current work assesses these low cost [7] R.M. Cleveland, A.K. Ghosh, and J.R. Bradley,materials to provide data for die design and is as such “Comparison of Superplastic Behavior in Two 5083an integral part in the knowlegde base necessary for Aluminum Alloys”, Mater. Sci. Eng. A, vol. 351, pp.the transition to happen. 228-236, 2003. [8] P.A. Friedman, S.G. Luckey, W.B. Copple, R. Allor, C.E. Miller, and C. Young, “Overview of SuperplasticREFERENCES Forming Research at Ford Motor Company”, J. Mater. Eng. Perform., vol. 13, pp. 670-677, 2004.[1] T.G. Nieh, J. Wadsworth, O.D. Sherby, Superplasticity [9] W.J. Kim, Y.K. Sa, H.K. Kim, and U.S. Yoon, “Plastic in Metals and Ceramics, Cambridge: Cambridge Forming of the Equal-Channel Angular Pressing University Press, 1997. Procesed 6061 Aluminum Alloy”, Mater. Sci. Eng. A,[2] J. Pilling, N. Ridley, Superplasticity in Crystalline vol. 487, pp. 360-368, 2008. Solids, London: The Institute of Metals, 1989. [10] P.A. Friedman, and W.B. Copple, “Superplastic Re-[3] R. Verma, P.A. Friedman, A.K. Ghosh, S. Kim, and C. sponse in Al-Mg Sheet Alloys”, J. Mater. Eng. Per- Kim, “Characterization of Superplastic Deformation form., vol. 13, pp. 335-347, 2004. Behavior of a Fine Grain 5083 Al Alloy Sheet”, Met- [11] K.T. Park, D.Y. Hwang, S.Y. Chang, and D.H. Shin, allurgical Mater. Transac. A, vol. 27A, pp. 1889-1898, “Low-Temperature Superplastic Behavior of a Sub- 1996. micrometer-Grained 5083 Al Alloy Fabricated by Se-[4] K. Kannan, J.S. Vetrano, and C.H. Hamilton, “Effects vere Plastic Deformation”, Metallurgical Mater. of Alloy Modification and Thermomechanical Proc- Transac. A, vol. 33A, pp. 2859-2867, 2002. essing on Recrystallization of Al-Mg-Mn Alloys”, Metallurgical Mater. Transac. A, vol. 27A, pp. 2947- 2957, 1996. 5

×