Experimental investigation on the weldability and forming behavior of aluminum alloy tailor-welded blanks

Aluminum alloy tailor-welded blanks (TWBs) have developed rapidly due to increasing interest and market pressure [J. M. Story, S. Heinemann, and S. Naegeler, Light Metal Age 56, 40–47 (1998). R. W. Davies, H. E. Oliver, M. T. Smith, and G. J. Grant, J. Minerals, Metals Mater. Soc. 51, 46–50 (1999)] from the automotive industry to further reduce the weight and cost of automotive components. In this study, a 5754-O aluminum alloy with a thickness of 1 mm was laser-welded by a 2 kW Nd: yttritium–aluminum–garnet (YAG) laser to produce a total of approximately 120 samples of TWBs with a similar thickness combination of 1 mm/1 mm. From the knowledge of the weld surfaces, weld profiles and tensile properties of the specimens of TWBs, the optimal welding parameters were identified and used to produce TWBs of varying widths and welding orientations for the Swift forming test. Thus, it was possible to measure and analyze the forming behavior, including the failure mode and the forming limit diagram (FLD), of the TWBs. Despite the limited power output of the Nd:YAG laser used in this study, a systematic study was undertaken to achieve welding the integrative aluminium alloy TWBs. In this study, applying a pulsed laser beam with an average power of 1100 W and a welding speed of 35 mm/s produced satisfactory TWBs. Despite some failures of the specimens at the welds during the tensile test, it was found that all TWBs yielded almost the same yield strength and ultimate tensile strength as those of their parent metal. TWBs with transverse welds also retained over 94% of their original ductility. Irrespective of the major loading direction during the forming test, the failures appeared somewhere away from the welds and heat-affected zones on the TWBs, with transverse welds such that the TWBs provided the same formability as the original 5754-O sheets. For TWBs with longitudinal welds, the failures were found to have initiated at the weld propagating perpendicularly to the major loading direction. This resulted in a lower level of FLD.