The effects of Ni and Au/Ni platings on laser welding of thin sheets

The effects of Ni and Au/Ni plating on laser seam welding of 200 μm thick aluminum, nickel, Kovar, and cold-rolled steel sheet in the lap-joint configuration has been studied. Seam welds were made using a pulsed Nd:YAG laser and a range of weld process conditions. The strength of the welds was characterized using tensile shear tests and all welds were examined metallographically. All material combinations were found to be weldable. The platings were not found to affect the range of process conditions that produced acceptable welds in the nickel, Kovar, and steel specimens. However, the Ni and Au/Ni platings reduced the power density required to form a joint in the aluminum specimens due to the higher absorptivity of Ni. In all cases, the power density which resulted in blowthrough was unaffected by the platings. The strength of the majority of the joints was equivalent to that of the annealed base material. The aluminum weld metal hardness was increased fourfold by alloying from the Ni plating and Au/Ni plating, but this did not affect the tensile shear strength of the joint because failure of the Ni and Au/Ni-plated Al specimens always occurred in the unalloyed softer heat affected zone. Not all of the higher melting point Ni and Au/Ni plating was melted during welding of the Al specimens and significant gas porosity was observed at the interface between the Al weld pool and the unmelted Ni and Au/Ni plating layers. However, this did not affect the tensile shear strengths of the Al welds. A Au/Ni braze joint was observed at the sheet interface adjacent to the fusion boundary of the Au/Ni-plated Ni, Kovar, and cold-rolled steel specimens. This did not affect the strength of the Kovar and cold-rolled steel specimens; however, the Au/Ni braze increased the strength of the Au/Ni-plated Ni specimens to that of the base material.