Formability of Friction-Stir-Welded Dissimilar-AluminumAlloy Sheets M.P. MILES, D.W. MELTON, and T.W. NELSON Friction stir welding (FSW) was investigated as a method for joining dissimilar-aluminum alloys 5182-O, 5754-O, and 6022-T4. These alloys are used in automotive applications in which parts consisting of dissimilar welded combinations of these alloys may be of interest. This study focuses on the formability of friction-stir-welded, dissimilar-alloy pairs of essentially the same gage, in order to investigate the mechanical properties that can be obtained using this approach. Testing showed that the properties of welded 5182/5754 alloy pairs retained reasonably good formability compared to base material performance. However, the 5182/6022 and 5754/6022 alloy pairs had significantly reduced formability compared to the base material properties, with failures occurring in the heat-affected zone (HAZ) of the 6022 or in the weld nugget itself. However, this level of formability was not much worse than that of monolithic, friction-stir-welded 6022.
I. INTRODUCTION
STAMPED metal parts are used widely in many industries, including automotive, appliance, and aerospace, in addition to having myriad smaller manufacturing applications. In some cases, the blanks used as starting material can be tailored in thickness to optimize weight. This tailoring has typically been done by welding sheets of differing thicknesses together, in a manner that allocates an appropriate amount of material to two or more separate areas, taking into account engineering and dimensional requirements. The blank is then stretch formed and drawn, resulting in a part with optimized weight. More recently, attempts have been made to weld dissimilar-aluminum alloys together, which ultimately could provide flexibility to designers who are trying to optimize strength, weight, and corrosion resistance.[1,2,3] Different welding techniques have been used to make tailored blanks. For aluminum alloys, laser welding, nonvacuum-electron-beam (NVEB) welding, or gas-tungsten-arc welding (GTAW) are used, because the high electrical and thermal conductivity of aluminum make mash-seam welding unsuitable.[4–7] One of the challenges in welding a tailored blank, as opposed to other situations in which a weld is a structural joint for a static member, is the forming process to which the weld is subjected. Tailored blanks for automotive stampings are typically stretch formed and drawn, resulting in large and complex strains in both the parent and weld material. Mechanical testing can be done to measure weld formability relative to the formability of the parent material, using both tension and various formability tests. A recent study was done to investigate the feasibility of joining dissimilar alloys via fusion welding using GTAW[1] as a welding process, while employing a special test (SigM.P. MILES, Assistant Professor, Manufacturing Engineering Technology, and T.W. NELSON, Associate Professor, Mechanical Engineering, are with the College of Engineering and Technology, Brigham Young University, Provo, UT 84602. Contact e-mail:
[email protected] D.W. MELTON, formerly Graduate Student, Manufacturing Engineering Technology, Brigham Young University, is Doctoral Candidate, Utah State University, Logan, UT 84322. Manuscript submitted July 9, 2004. METALLURGICAL AND MATERIALS TRANSACTIONS A
majig test) to evaluate the cracking susceptibility of various dissimilar combinations of 5182-H16, 5754-O, 6022T4, and 6111-T4. The results of this work showed that cracking resistance during welding was highest for the 5182/5754 alloy pair, while combinations of 6022 with either 5754 or 5182 resulted in the lowest cracking resistance. Work has also been done on friction stir welding (FSW) of a cast A356 aluminum alloy to a wrought 6061 aluminum alloy.[3] The results from this study showed that good, defectfree welds were produced using FSW, but that the transverse tensile ductility of the welded materials was governed by the weaker alloy, which in this case was the A356. The difficulties that have been observed in obtaining good mechanical properties when joining dissimilar alloys with traditional fusion welding methods[1] have led us to investigate the possibility of using FSW for this purpose. In this work, we have compared base metal properties for three aluminum alloys with properties of friction-stir-welded sheets that were joined in dissimilar combinations. We have also compared the dissimilar-alloy joints with some prior results obtained by friction stir welding same-alloy sheets. II. EXPERIMENTAL PROCEDURES A. Materials Alloys 5182-0, 5754-0, and 6022-T4, of similar gage, ranging from 1.98 to 2.03 mm, were used for welding experiments. Note that the purpose of this study is not to weld the sheets of alloys with dissimilar gages, which typically have much greater gage differences (for example, 1.0 to 1.5 mm). Instead, the goal of this work is to evaluate the mechanical properties that can be obtained by joining the sheets of dissimilar alloys, using FSW. The sheets under review are automotive alloys and are, therefore, candidates for use in tailored-blank applications. Alloys 5182-O and 5754-O are both in the annealed condition and, as a result, they strengthen significantly with the cold work that occurs during plastic deformation. The 5xxx-series alloys are used primarily for inner body panels. The 6022-T4 alloy is partially hardened and is formable enough to manufacture stamped parts. One of the main applications for this alloy VOLUME 36A, DECEMBER 2005—3335
Table I. Automotive Aluminum Alloys Composition (Wt Pct) Material
Gage
Si
Fe
Cu
Mn
Mg
Cr
Ni
Zn
Ti
5182-O 5754-O 6022-T4
2.03 mm 1.98 mm 2.03 mm
0.2 0.4 0.6 to 1.2
0.35 0.4 1
0.15 0.1 0.4 to 0.9
0.2 to 0.5 0.5 0.8
4 to 5 2.6 to 3.6 0.6 to 1.2
0.1 0.3 0.3
0 0 0.2
0.25 0.2 1.5
0.1 0.15 0.2
is exterior body panels, which are painted and then baked in an oven. The paint-baking process artificially ages this alloy and increases the strength of the final part, compared to the initial T4 temper. Table I shows the compositions of these materials. B. Welding Experiments The friction stir welds were produced at speeds of 500 to 1500 rpm and at feed rates of 13 to 40 cm/min. A drawing of the tool used for the experiments is shown in Figure 1. After the appropriate profile of the tool was machined from H13 tool steel, it was heat treated. The tool has a concave section at the base of the pin that traps material during welding, while forging it back down the threads into the joint. The threads are approximately one for every millimeter of pin length. The properties of the friction-stir-welded joint vary significantly, depending on the speed (rpm) and feed (cm/min) of the tool, so a series of experiments is usually necessary to optimize processing conditions, in order to achieve the best results.
Fig. 1—Drawing of FSW tool.
C. Microhardness Measurements Transverse samples were removed from representative welds, for microhardness and metallographic evaluations. The heat-sensitive 6xxx-series samples were mounted in epoxy. All samples were polished in steps from 320-grit sandpaper to 0.5-m diamond paste. Vickers microhardness tests were done with an eight-second dwell at 100 g. The indents were done on the exposed cross section of the weld, 0.64 mm from the top and 0.64 mm between each indent. The 6022 alloy was prevented from naturally aging (samples were stored below 0°C) before being tested. D. Formability and Tensile Testing Tensile specimens were made using the ASTM E8 standard, with a gage width of 12.5 mm and a gage length of 63.5 mm. In each case, the weld was positioned transverse to the tensile axis in the middle of the gage length, with the rolling direction along the tensile axis. Mechanical evaluation of welded sheet specimens can be done using a tension test, with the weld transverse to the tensile axis, where failures occurring in the base metal away from the weld are considered to be acceptable. Formability testing can also be employed to evaluate the performance of the welded sheets. Typical tests include the limiting dome height (LDH) test[8,9] and the Ohio State University (OSU) test.[10,11,12] These tests are designed to simulate planestrain stretch failures, with minimal bending strain. The LDH test can also be used to impose biaxial stretching on a sheet specimen in what is often referred to as a full-dome test. 3336—VOLUME 36A, DECEMBER 2005
Fig. 2—Specimen used for LDH and OSU tests, with the weld and the rolling direction along the major axis of the specimen.
Both the LDH and the OSU tests were used in this work. The specimen geometries for LDH and OSU testing were similar, with the weld lines and the rolling directions along the major axis of the specimen (Figure 2). The root side of the weld was facing in, against the punch, for all tests performed. Finally, some forming limit diagrams (FLDs) were generated experimentally, using the dissimilar-welded-alloy pairs. An FLD is a plot of major-vs-minor strain in the plane of the sheet, for different strain ratios.[13,14] At each minor strain, there is a limiting major strain that can be achieved before failure. The locus of the points for different ratios of limiting major strain/minor strain is the forming limit curve (FLC); this represents a boundary below which “safe” ratios of major-to-minor strain exist. In order to measure surface strains, grid circles were electrochemically etched on the aluminum sheets, with diameters averaging 2.36 mm. Samples of varying widths were made up with welds along the major axis and tested, using different levels of lubrication and different specimen widths. This is clearly a different METALLURGICAL AND MATERIALS TRANSACTIONS A
case than the standard procedure of testing unwelded sheets with uniform properties. In this case, the weld and the heataffected zone (HAZ) represent inhomogeneities or potential weaknesses, where strains can localize more rapidly than in unwelded, relatively homogeneous sheets. In addition, the specimens are composed of welded dissimilar alloys having different base strengths, which influence both the strain patterns in the specimen and the eventual location of failure. The difference in the present case, compared to the standard approach, is that the eventual location of failure could occur in either of the two alloys away from the weld, in the HAZ, or in the weld itself; this location had to be determined by several trials, so that interrupted testing could provide strain ratios just before and after the failure occurred. In order to get different strain ratios before and after failures, the standard procedure of using different blank widths and lubrications was employed. The circles used for plotting the FLC had either no neck, an incipient neck, or a deep neck. If there was no neck, the strains were plotted as being safe, while incipient or deep necks were plotted as “fail”. In these welded blanks, the 5182/5754 specimens failed in typical fashion, with the split occurring perpendicular to the major strain axis and to the weld. However, the 5182/6022 and 5754/6022 specimens often had splits that were parallel to the weld, in the HAZ of the 6022 material. The measurement of the major and minor axes of the circles was performed with an optical-imaging machine. These measurements were used to compute true major and minor strains on each specimen, and then were plotted on the FLD.
III. RESULTS AND DISCUSSION A preliminary assessment of weld ductility was performed using a full-dome LDH test, to evaluate how weld properties were affected by various tool feeds and speeds applied to the three alloy pairs: 5182/5754, 5182/6022, and 5754/ 6022. Welding feed rates were 13, 24, and 40 cm/min, while welding speeds were 500, 1000, and 1500 rpm. The results of this testing eliminated the 500 rpm and 13 cm/min parameters, because all failures occurred in the weld during dome testing. The combinations of the other parameters resulted in most failures occurring outside the weld nugget, which was considered acceptable, as seen, for example, in Figure 3. A summary of the results for the acceptable welding parameters is shown in Table II. Further tensile and formability testing for each alloy pair was then done on specimens that were produced using these acceptable welding parameters. A summary of the transverse tensile results for dissimilar-alloy pairs produced at various processing speeds are shown in Table III (average of 10 specimens in each case). Although failures did not occur in the weld for any of the 5xxx-series specimens tested, the transverse results for these specimens were governed by the strength of the weakest alloy, which in this case is 5754. Therefore, deformation is concentrated in the 5754 part of the tensile specimen, resulting in a lower total elongation compared to the frictionstir-welded, same-alloy pairs, as shown in Figure 4(a). The same-alloy-pair data were obtained from a prior study,[15] where sheets were butt welded together, as in this current work, using similar welding parameters; however, in that study, only same-alloy specimens were welded. When 6022 METALLURGICAL AND MATERIALS TRANSACTIONS A
Fig. 3—A failure outside of the weld was considered an acceptable result for the full-dome tests (example shown is for 5182/6022). For combinations with alloy 6022, most dome-test failures occurred at the edge of the weld, in the HAZ of the 6022 material.
Table II. Summary of Dome-Test Results (Average of Five Specimens)
Alloy Pair 5182/5754
5182/6022
5754/6022
Feed (cm/min) Speed (rpm)
Average Stroke at Failure (mm)
Failure Location
24 1000 40 1000 24 1500 40 1500 24 1000 40 1000 24 1500 40 1500 24 1000 40 1000 24 1500 40 1500
27.5 28.7 26.2 25.5 18.0 14.6 18.6 17.5 19.9 17.5 20.7 17.1
base 5754 base 5754 base 5754 base 5754 HAZ 6022 HAZ 6022 HAZ 6022 HAZ 6022 HAZ 6022 HAZ 6022 HAZ 6022 HAZ 6022
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Table III. Tension-Test Results for the Dissimilar Welded Sheets Alloy Pair 5182/5754
5182/6022
5754/6022
Feed (cm/min) Speed (rpm)
Ultimate Tensile Strength (MPa)
Pct Total Elongation
Failure Location
24 1000 40 1000 24 1500 40 1500 24 1000 40 1000 24 1500 40 1500 24 1000 40 1000 24 1500 40 1500
228.0 224.0 231.0 224.0 226.0 221.0 218.0 225.0 223.0 227.0 229.0 226.0
18.8 19.1 18.4 18.0 13.7 11.0 12.6 12.2 11.3 10.0 11.0 11.0
90 pct base 5754/10 pct weld nugget 100 pct base 5754 100 pct base 5754 80 pct base 5754/20 pct weld nugget 100 pct HAZ 6022 100 pct weld nugget 100 pct HAZ 6022 100 pct HAZ 6022 80 pct weld nugget/20 pct HAZ 6022 100 pct weld nugget 100 pct weld nugget 100 pct weld nugget
(a)
(b)
(c) Fig. 4—Total elongation of best-performing transverse-tensile specimens made from the welded-alloy pairs of (a) 5182/5754, (b) 5182/6022, and (c) 5754/6022. In each plot, the friction-stir-welded, monolithic-alloy performance is shown, for comparison.
was welded to either 5182 or 5754, failures occurred near the weld, in the 5182/6022 pair, or mainly in the nugget, for the 5754/6022 pair. The 5182/6022-alloy-pair elongation was a few percent lower than the welded 6022 specimens, as seen in Figure 4(b), while the 5754/6022 pair had about the same total elongation as the welded 6022 (with many failures occurring in the weld, on the 5754 side), as seen in 3338—VOLUME 36A, DECEMBER 2005
Figure 4(c). The main conclusion from these results is that a 6022 sheet welded to either 5182 or 5754 does not appear to have significantly worse transverse tensile ductility than that of monolithic 6022 sheets friction stir welded together. In the 5182/6022 specimens, failures occurred mostly in the HAZ of the 6022, although some failures did occur in the weld nugget itself. In the case of the 5754/6022 alloy pair, METALLURGICAL AND MATERIALS TRANSACTIONS A
Fig. 7—Transverse-hardness profile for a 5182/6022 friction stir weld (the 5182 is left of center and the 6022 is right of center). Fig. 5—Acceptable failure locations for the three alloys pairs. The top is 5182/6022, the middle is 5182/5754, and the bottom is 5754/6022.
Fig. 8—Transverse-hardness profile for a 5754/6022 friction stir weld (the 5754 is left of center and the 6022 is right of center). Most specimens failed in the weld, but some failed at the edge of the weld, on the 6022 side. The hardness of 5754, in one of the specimens that failed in the HAZ of the 6022, is also shown, indicating the possibility that the work hardening in the 5754 could be sufficient, in some cases, to cause a failure in the soft HAZ on the 6022 side of the specimen. Fig. 6—Transverse-hardness profile for a 5182/5754 friction stir weld (the 5182 is left of center and the 5754 is right of center).
most failures occurred in the weld nugget, but some of them occurred in the HAZ in the 6022. Favorable failures for the three cases are shown in Figure 5. Microhardness results for the 5182/5754 pair are shown in Figure 6. The 5182 is a higher-strength alloy than the 5754, and this is seen in the hardness profile moving from the 5182 side of the specimen to the 5754 side, where a fairly abrupt drop in hardness occurs at the transition between the weld nugget and the thermomechanically affected zone (TMAZ). Some work hardening has occurred in the weld nugget itself, resulting in a greater hardness than in the base materials. Profiles for the 5182/6022 and 5754/6022 pairs are shown in Figures 7 and 8. The 5182/6022 weld displays a soft area on the 6022 side of the specimen in the HAZ; this is where most of the specimens failed. For the 5754/6022 weld, there is a less evident drop in hardness on the 6022 side of the specimen, compared to the hardness in the weld itself. Most failures actually occurred in the weld nugget (80 pct), but 2/10 of the failures did occur in the HAZ of the 6022, as seen in the hardness of the 5754, for a specimen that had failed in the HAZ of the 6022 (Figure 8). In these cases, it is possible that the work hardening of the 5754 during tension testing was sufficient to force the failure to occur in the HAZ of the 6022. METALLURGICAL AND MATERIALS TRANSACTIONS A
Fig. 9—Cross section of a friction-stir-welded 5754/6022 alloy pair. The 5754 is the lighter-colored alloy on the left. The interface between the two alloys is clearly defined. In this alloy, most fractures (80 pct) occurred in the weld nugget in the 5754 side, as shown by the arrow. In 20 pct of the cases, fractures occurred in the HAZ of the 6022, as shown.
Failures that occurred in the weld nugget were positioned closer to the 5754 side of the specimen, where the weld is mostly composed of 5754 material. A cross section of this weld is shown in Figure 9, where the interface between the 5754 and 6022 alloys is clearly defined and the failure locations are indicated. While the transverse tension tests caused in-plane stretching across the weld, OSU tests were used to impose planestrain stretching along the weld, using a cylindrical punch. The results for OSU testing are shown in Table IV. There is essentially no difference between the performance of the base material and that of the dissimilar pairs, for this testing. Therefore, plane-strain formability of the welded dissimilar alloys is very good, when stretching is done along the weld and not across it. VOLUME 36A, DECEMBER 2005—3339
the FLD for the 5182/5754 pair. Figures 10(b) and (c) show the FLDs for unwelded 5182 and 5754, and for friction-stirwelded, monolithic 5182 and 5754. In contrast to the FLDs of both the welded and unwelded monolithic alloys, which have a minimum formability at plane strain, and then have greater formability as the strain ratios become biaxial, the 5182/5754 pairs appear to have a relatively flat curve, with similar levels of formability for both the plane-strain and the more biaxial-strain ratios. The observation of specimens used to measure forming limits under biaxial-strain conditions provides a possible explanation for this behavior. The weld line moved during stretching; this was caused by more deformation in the weaker 5754 alloy, where the specimen failure eventually occurred. This is seen in Figure 11. The weld-line
The right-hand sides (positive minor and major strains only) of the FLD for the 5182/5754, 5182/6022, and 5754/6022 alloy pairs were experimentally measured. Figure 10(a) shows Table IV. Plane-Strain OSU-Testing Results Specimen
Average Punch Stroke at Failure (mm)
Standard Deviation (mm)
5182 5754 6022 5182/5754 5182/6022 5754/6022
30.3 29.3 30.9 29.9 29.3 29.2
0.3 0.3 0.3 0.3 0.4 0.5
(a)
(b)
(c) Fig. 10—The FLD for a (a) 5182/5754 alloy pair. The specimens were fabricated using a feed rate of 40 cm/min and a tool speed of 1000 rpm. The forming limit appears to be relatively flat, from plane-strain toward more biaxial stretching, compared to the (b) base alloys and (c) friction-stir-welded, monolithic alloys. Failures occurred in the lower-strength 5754 side of the blank, and major strains were lower for a given minor strain than in the monolithic-alloy results. 3340—VOLUME 36A, DECEMBER 2005
METALLURGICAL AND MATERIALS TRANSACTIONS A
Fig. 11—The weld line on the 5182/5754 blank is shifted during biaxial stretching, so that more minor strain (perpendicular to the weld in this case) occurs in the weaker 5754 side of the blank than in the monolithic, frictionstir-welded 5754. This results in limit-strain ratios that have greater minor strains at a given major strain, resulting in a relatively flat FLC.
Fig. 13—The FLD for a 5754/6022 alloy pair. The specimens were fabricated using a feed rate of 24 cm/min and a speed of 1000 rpm.
IV. SUMMARY AND CONCLUSIONS Aluminum-alloy sheets of 5182-O, 5754-O, and 6022-T4 were joined in dissimilar combinations, using FSW. Various tests were performed in order to characterize the ductility of the resulting welded alloy pairs. The following conclusions were drawn from the test results.
Fig. 12—The FLD for a 5182/6022 alloy pair. The specimens were fabricated using a feed rate of 24 cm/min and a speed of 1000 rpm.
shift caused by pairing a weaker alloy (5754) with a stronger alloy (5182) results in relatively more minor strain, at a given level of major strain, in the 5754 side of the blank. This result appears to be similar to that seen in prior work on finite-element simulation of dissimilar alloy and gage combinations in aluminum tailored blanks.[16] The level of formability represented by this relatively flat curve is similar to the level exhibited by the base alloys in plane strain. For the 6022 welded to 5182 or 5754, the plane-strain condition results in maximum formability, and then drops rapidly as more minor strain occurs, as seen in Figures 12 and 13. These FLDs are similar to those of friction-stir-welded, single-alloy 6022 blanks, where the softening that occurs during welding results in a weak area that is exploited, especially when stretching is imposed across the weld during biaxial straining. METALLURGICAL AND MATERIALS TRANSACTIONS A
1. No softening occurred in the 5182/5754 alloy pair, because these alloys were in the annealed condition. However, softening did occur in the 6022 side of the 5182/6022 and 5754/6022 alloy pairs. 2. Dome testing was effective for discriminating between an acceptable weld and a bad weld. This test causes biaxial strain in the weld area, resulting in stretching across the weld and subsequent splitting in the weld nugget, if the welding parameters are not good. 3. Transverse-tension tests showed that total elongation is a function of the weakest alloy in the welded pair. For the 5182/5754 pair, stretching was concentrated in the 5754 half of the specimen. For the 5182/6022 and 5754/ 6022 pairs, strain localized in the HAZ on the 6022 side of the weld or in the weld nugget. 4. The OSU plane-strain testing showed that, when stretching is done only along the weld (without any transverse stretching), the ductility of the welded dissimilar-alloy pairs is about the same as that of the base materials. 5. The FLD of 5182/5754 appears to have a relatively flat FLC, exhibiting similar formability both in plane-strain and in biaxial-tension conditions. This is caused by the strength difference in the two alloys, where more strain occurs in the weaker alloy, as is seen in the shifting of the weld line during testing. This results in relatively more minor strain at a given major limit strain. 6. The FLDs for 5182/6022 and 5754/6022 have curves that are maximum at plane strain and that slope toward minimum values as strain ratios approach biaxial tension. This behavior is caused by the localization of strain in the HAZ of the 6022 alloy, especially as biaxial-strain VOLUME 36A, DECEMBER 2005—3341
conditions cause stretching across the weld, and is similar to that of monolithic, friction-stir-welded 6022.
ACKNOWLEDGMENT The authors thank Sherri McCleary of Alcoa Technical Center for supplying the sheet alloys used for this study.
REFERENCES 1. M.M. Mossman and J.C. Lippold: Welding J., 2002, Sept., pp. 188S-194S. 2. W.B. Lee, Y.M. Yeon, and S.B. Jung: J. Mater. Sci., 2003, vol. 38, pp. 4183-91. 3. J.H. Ouyang and R. Kovacevic: J. Mater. Eng. Performance, 2002, vol. 11 (1), pp. 51-63. 4. P.A. Friedman and G.T. Kridli: J. Mater. Eng. Performance, 2000, vol. 9 (5), pp. 541-51.
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5. A. Buste, X. Lalbin, and M.J. Worswick: Proc. Int. Symp. on Light Metals, M. Bouchard and A. Faucher, eds., Canadian Institute of Mining, Metallurgy, and Petroleum, Montreal, 1999, pp. 485-500. 6. R.W. Davies, G.J. Grant, H.E. Oliver, M.A. Khaleel, and M.T. Smith: Metall. Mater. Trans. A, 2001, vol. 32A, pp. 275-83. 7. E.R. Pickering, M.A. Glagola, R.M. Ramage, and G.A. Taylor: 1995 Int. Congr. Expo. Meeting, Society of Automotive Engineers, Warrendale, PA, pp. 67-73. 8. A.K. Ghosh: Met. Progr., 1975, May, pp. 52-54. 9. A.K. Ghosh: Met. Eng. Q., 1975, Aug., pp. 53-64. 10. M.P. Miles, J.L. Siles, R.H. Wagoner, and K. Narasimhan: Metall. Trans. A, 1993, vol. 24A, pp. 1143-51. 11. Y.S. Suh and R.H. Wagoner: J. Mater. Eng. Performance, 1996, vol. 5, pp. 489-99. 12. R.H. Wagoner, W. Wang, and S. Sriram: J. Mater. Processing Technol., 1994, 45, pp. 13-18. 13. S.P. Keeler and W.A. Backofen: Trans. ASM, 1963, vol. 56, pp. 25-48. 14. S.S. Hecker: Sheet Met. Ind., 1975, Nov., pp. 671-76. 15. M.P. Miles, D. Melton, and T.W. Nelson: Metall. Mater. Trans. A, 2004, vol. 35A, pp. 3461-68. 16. A.V. Bhagwan, G.T. Kridli, and P.A. Friedman: NAMRC XXXI Conf., Hamilton, ON, Canada, Society of Manufacturing Engineers, Dearborn, MI, 2003, pp. 1-8.
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