Materials & Advanced Manufacturing (M&AM) DISSIMILAR - PowerPoint PPT Presentation

Materials & Advanced Manufacturing (M&AM) DISSIMILAR FRICTION STIR WELDING OF A SOLID SOLUTION-STRAIN HARDENED ALUMINUM 5083 ALLOY AND PRECIPITATION STRENGTHENED ALUMINUM 2139 AND ALUMINUM 7085 Martin McDonnell, US Army TARDEC Dr. Nelson Martinez, Concurrent Technologies Corporation DISTRIBUTION STATEMENT A. Approved for public release; distribution unlimited 8/10/2018 1

Materials & Advanced Background & Objectives Manufacturing (M&AM) • In this study, dissimilar aluminum alloys were joined using a solid phase welding process known as friction stir welding (FSW) • The most common aluminum alloy employed by the US Army, AA5083-H131, was friction stir welded (FSW) to AA2139-T8 and AA7085-T721 • AA2139 and AA7085, two of the newest high strength aluminum armor alloys developed for increased ballistic protection, were also welded to each other as part of this study • FSW was selected as the most feasible joining process due to the precipitation strengthened alloys not being advantageous to fusion welding processes • The objective of the study was to evaluate the weldability of dissimilar aluminum alloys and study the affects of material placement on the advancing side vs. the retreating side of the FSW tool • Mechanical characterization results of the weldments are presented here 8/10/2018 DISTRIBUTION A: UNLIMITED DISTRIBUTION 2

Materials & Advanced Materials & Methods Manufacturing (M&AM) • Aluminum alloys • Solid solution, strain hardened AA5083-H131 • Precipitation strengthened AA2139-T8 and AA7085- T721 • FSW tooling • MP159 Ni-Co based alloy MP159 FSW Tool • Tapered w/ 14 threads per inch (TPI) • 5 flats • Joint design • Plates were 2 in. thick, 24 in. long and 6 in. wide • Butt joint configuration • Testing performed to date • Tensile, side bends and microhardness FSW Process • Macroetching and optical microscopy 8/10/2018 3

Materials & Advanced Friction Stir Welded Hull Manufacturing (M&AM) 8/10/2018 4

Materials & Advanced Manufacturing (M&AM) 2-inch thickness AA7085-T721 (advancing side) welded to AA2139-T8 (retreating side)

Materials & Advanced Macroetching Manufacturing (M&AM) • Macro cross-sections were taken at 5 and 18 inches from the start of the weld • A visual inspection of the macroetch samples showed cracks and voids in the weld nugget as shown in the images below Spindle Speed: 110 rpm Tool Velocity: 2 ipm 8/10/2018 6

Materials & Advanced Bend Testing Manufacturing (M&AM) • Bend specimens were also taken from welded plate just before of each macro cross- section • The results of the testing showed cracking in the weld as observed from the figures below 8/10/2018 7

Materials & Advanced Tensile Testing Manufacturing (M&AM) • Tensile tests showed a 43.2 ksi UTS, 29.6ksi YS, 9.6% elongation with a 65% joint efficiency Ultimate Yield Stress % EL Joint Sample Stress (ksi) (ksi) Eff. 7085-T721 68 60 12 - 2139-T8 67 64 9 - 2139-T8 to 43.2 29.6 9.6 65% 7085-T721 • Failure occurred in the weld nugget 8/10/2018 8

Materials & Advanced Observations Manufacturing (M&AM) • Testing results showed that AA7085-T721 in the advancing side and AA2139-T8 in the retreating side led to a weld with cracks and voids in the weld nugget thus resulting ineffective joint efficiencies • This ensued to another weld in which AA7085-T721 was placed in the retreating side and the AA2139-T8 was placed in the advancing side of the tool and the same characterization was performed 8/10/2018 9

Materials & Advanced Manufacturing (M&AM) 2-inch thickness AA2139-T8 (advancing side) welded to AA7085-T721 (retreating side)

Materials & Advanced Macroetching Manufacturing (M&AM) • Same welding parameters were used but the advancing side of the tool was placed in the AA2139-T8 • Macro cross-sections were taken at 6 and 17 inches from the start of the weld • Images showed no cracks or voids in the weld nugget indicating a good mixing of the two alloys 8/10/2018 11

Materials & Advanced Bend/Tensile Testing Manufacturing (M&AM) • Bend specimens were taken from weld plate next to macro cross-sections as previously done on the first weldment • Bend specimens show very minor cracking in the weld as observed from the figures below 8/10/2018 12

Materials & Advanced Bend/Tensile Testing Manufacturing (M&AM) • Tensile tests showed an 8.6% increase in UTS, a 5.1% increase in YS, a 32.3% increase in elongation with a joint efficiency increase of 7.7% Ultimate % EL Sample Yield Stress (ksi) Joint Eff Stress (ksi) 7085-T721 68 60 12 2139-T8 67 64 9 2139-T8 to 7085-T721 46.9 31.1 12.7 70% 7085-T721 to 2139-T8 43.2 29.6 9.6 65% • This time the failure appeared in the Heat Affected Zone (HAZ) of the AA7085-T721 8/10/2018 13

Materials & Advanced Tensile Observations Manufacturing (M&AM) • Clearly there is a difference in mechanical properties depending on which metal is placed on the advancing side. • As was observed by the tensile tests, failure occurred in the HAZ of the AA7085-T721. • This indicates that the dissipation of heat is more detrimental on the AA7085-T721 alloy. 8/10/2018 14

Materials & Advanced Macrohardness Testing Manufacturing (M&AM) • There is a clear division in hardness values observed in the nugget (the values average 130 HV in the AA2139-T8 nugget while the AA7085-T721 average 160 HV) • Clearly there is a division between the two aluminum alloys in the nugget • As observed from the hardness profiles, the weakest part of the weld is in the HAZ of the AA7085 (~88 HV) Bottom of Weld… 2139 7085 Top of Weld… 2139 7085 160 160 140 140 HV 0.3 HV 0.3 120 120 100 100 Distance (mm) Distance (mm) 80 Middle of Weld (1") 7085 80 2139 -50 -30 -10 10 30 50 -50 -30 -10 10 30 50 HV 0.3 130 Distance (mm) 80 -50 -30 -10 10 30 50 8/10/2018 15

Materials & Advanced Base Metal Microscopy Manufacturing (M&AM) AA2139 AA7085 100X 100X 500X 500X 8/10/2018 16

Materials & Advanced Weld Nugget Microscopy Manufacturing (M&AM) b a c b c a e d e d 2139 f g 7085 f g It does appear there is a locking mechanism in place joining the two different alloys. • • However, a clear division between the AA2139-T8 and AA7085-T721 within the nugget is observed. 8/10/2018 17

Materials & Advanced Weld Nugget Microscopy Manufacturing (M&AM) • Grains refinement over both base materials is clearly observed in the weld nugget • From the images, there appears to be recrystallization of the existing parent material grains into finer grains • However, the optical images do show a clear separation of the grains between the AA2139-T8 and AA7085-T721 b c a as welded as welded e d AA7085 AA2139 d e f g base 500X 500X 8/10/2018 18

Materials & Advanced Manufacturing (M&AM) 2-inch AA5083-H131 / AA7085-T721

Materials & Advanced Macroetching Manufacturing (M&AM) • Weld parameters started with spindle speed of 130 RPM and decreased spindle speed of 110 RPM, since it was expected that it would provide less heat with reduction in rotational rate • Macro cross-sections were taken at positions 6, 13 and 18 inches from the start of the weld No cracks or voids observed in the macroetches indicates that there is good mixing of the • two alloys 8/10/2018 20

Materials & Advanced Bend/Tensile Testing Manufacturing (M&AM) • The 130 RPM section showed no cracks in the weld nugget (start of the weld) • None of the weld nugget cracks extended through the bend specimen thickness 130 rpm 120 rpm 110 rpm • Specimen from 130 RPM broke in the weld nugget on the advancing side (AA5083) Specimens from 120 rpm & 110 rpm broke outside the weld nugget on the retreating side • (AA7085) in the HAZ Spindle Speed (rpm) Ultimate Stress (ksi) Yield Stress (ksi) Elon. (%) Joint Eff. 5083 Joint Eff. 7085 AA7085 68 60 12 AA5083 45 37 8 130 RPM 42.8 26.3 10.6 95% 63% 120 RPM 46.2 25.7 16.1 103% 68% 110 RPM 46.4 26.2 19.1 103% 68% 8/10/2018 21

Materials & Advanced Macro/Hardness Testing Manufacturing (M&AM) • A division in hardness values is observed in the nugget • 120 HV in the AA5083-H131 weld nugget and 160 HV in the AA7085-T721 weld nugget • The hardness profiles show three minima values • The nugget, 7085 HAZ, and 5083 HAZ & failure will occur at any of these locations • Failure in the HAZ of AA7085 and the nugget occurred during tensile testing • The strength in the HAZ is ultimately dictated by the heat dissipated throughout the weld Top of Weld (.25") 7085 5083 5083 7085 Bottom of Weld… 160 160 140 140 5083 7085 HV 0.3 HV 0.3 120 120 100 100 5083 7085 80 Distance (mm) Middle of Weld… 160 80 Distance (mm) -50 -30 -10 10 30 50 -50 -30 -10 10 30 50 140 HV 0.3 120 100 80 Distance (mm) -50 -30 -10 10 30 50 8/10/2018 22

Materials & Advanced Base Metal Microscopy Manufacturing (M&AM) AA5083 AA7085 100X 100X 500X 500X 8/10/2018 23