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.

Microresistance spot welding of 0.2–0.5 mm thickness Kovar, steel, and nickel using different types of power supply was investigated. The effects of process parameters (welding current/pulse energy, electrode force, and welding time/pulse width) on joint strength and nugget diameter were studied. The maximum values of welding current and nugget diameter that did not result in weld metal expulsion and/or electrode–sheet sticking were determined. The difference between micro- and ‘large scale’ resistance spot welding was also considered. It was noted that the difference between micro- and large scale resistance spot welding is due not only to the difference in the scale of the joints, but also to the fundamental difference in the electrode forces (pressures) used. Based on the results of the present work, nominal process parameters are recommended for microresistance spot welding of Kovar, steel, and nickel when using different power supplies.

An investigation has been conducted of the weldability of 0.2-mm-thick sheet aluminum, brass, and copper in small-scale resistance spot welding using a high-frequency inverter and a capacitor-discharge power supply. The results have been compared to those of previous investigations using a line-frequency alternating current power supply. The effects of electrode materials and process parameters on joint strength, nugget diameter, weld-metal expulsion and electrode-sheet sticking were studied. This work has also provided practical guidelines for selection of power supplies, process parameters (welding current/pulse energy, welding time/pulse width, electrode forces, etc.) and electrode materials for small-scale resistance spot welding of thin sheet aluminum, brass and copper.

In electronic products and devices, base metals such as Al, brass, steels, Cu, Kovar and Ni are often plated with materials such as Ni, or Ni and then Au to enhance the corrosion and oxidation resistance or to improve the decorative appeal of the substrates. In this study, laser seam welds were performed on 200 mum thick sheets Al, Ni, Kovar and cold-rolled, plain carbon steel (CRS) in the lap-joint configuration using a Lumonics JK702H Nd:YAG pulsed laser welder. Uncoated, Ni and Au/Ni plated sheet was used. Tensile shear tests were performed and weld dimensions and weld microstructures were examined. Except for the Al specimens, the coatings did not affect the minimum beam intensity necessary for joining at the sheet interface. Once the weld pool penetrated across the interface into the second sheet, there was a very rapid increase in joint strength to a maximum strength value that was always less than the base metal strength. In almost all cases, failure occurred by shear in the heat affected zone (HAZ) at the fusion boundary. The Au/Ni plated Ni, Kovar and CRS specimens exhibited a Au/Ni braze at the sheet interface adjacent to the fusion boundary due to melting of the Au/Ni plating layers. In most cases, the shear strength of the joints was not affected by the plating; however, the presence of the Au/Ni braze caused a shift of the failure location away from the fusion boundary and into the HAZ or base metal.

The resistance weldability of 0.2-mm-thick sheet aluminum, brass, and copper in small-scale resistance spot welding (SSRSW) was studied. The effects of electrode materials and process parameters on joint strength and nugget size were investigated. The welding current ranges for SSRSW of the sheet metals were determined based on the minimum current that produced a required nugget diameter and maximum currents that did not result in electrode-sheet sticking or weld metal expulsion. A qualitative analysis indicated that resistance weldability of the metals is not only determined by their resistivity (or thermal conductivity) but is also affected by other physical properties (such as melting point, latent heat of fusion and specific heat).