Interfacial structure and micro and nano-mechanical behavior of laser-welded 6061 aluminum alloy blank

1 mm thick tailor-welded blank of 6061 alloy has been fabricated by Nd: YAG laser welding. The microstructure and the failure mechanism of the welded blank are investigated using optical microscope, atomic force microscope, energy dispersive spectroscopy, microindentation, and nanomechanical tester. The dendrite structure exists at the fusion zone. The partially melted zone is found near the fusion line. The tensile tests show that the welded alloy exhibits lower strength and ductility than the base alloy, and failure occurs at the partially melted zone during tensile testing. Combined nanoindentation with in-situ AFM imaging reveal that the hardness at the partially melted zone is distributed inhomogeneously on the microscopic scale. The hardness at the area adjacent to the grain boundary is lower than that at the center of grain. This is responsible for the failure upon tensile loading, and attributed to the loss of strength and ductility of the welded blank on a macroscopic scale.