Effects of Au plating on dynamic resistance during small-scale resistance spot welding of thin Ni sheets

Abstract

The effects of Au plating on dynamic resistance during small-scale resistance spot welding of thin Ni sheets have been investigated. Compared to the small-scale resistance spot welding of bare Ni, the Au-plated material showed much lower initial static resistance, and the contribution of constriction resistance to overall dynamic resistance reduced to a negligible value very early in the welding sequence because of the low softening temperature and its lack of surface oxide film. For the same reason, the asperity heating and surface breakdown stages during resistance spot welding of bare Ni were not observed during resistance spot welding of Au-plated Ni. Furthermore, the partial surface melting stage was replaced by the solid-state bonding and brazing stages.Step increases in the sheet-to-sheet dynamic resistance curves of Au-plated Ni were shown to be due to the peripheral unzipping of a prior solid-state bond caused by uneven local thermal expansion. The electrode-to-electrode dynamic resistance curve when welding Au-plated material is not useful for monitoring the state of nugget formation.

Ultrafast Parallel Micro-Gap Resistance Welding of an AuNi9 Microwire and Au Microlayer

“…When the parameters were small (0.200 kA, 3 ms, and 9.8 N), the heat generated was not enough to cause the materials to melt. At this time, the AuNi 9 microwires and Au layers were only slightly softened, and only one peak was observed in the dynamic resistance curve ( Figure 7 a) [ 25 , 26 ]. With the increase in parameters, a second peak was observed, indicating the formation of the nugget.…”

Resistance microwelding of crossed Pt–10Ir and 316 LVM stainless steel wires

“…In the final stage of the resistance welding process, either mechanical collapse of the joint or loss of material due to expulsion causes shortening of the current path, causing a second reduction in bulk resistance 20 –. 22…”

“…Dynamic resistance measurements have been found to be very useful in studying the nugget formation for both LSRSW 21 and RMW processes. 20,22 In the conventional sheet to sheet resistance welding of similar materials, different stages of the welding process have been identified. In the first stage, the resistance drops due to surface breakdown, asperity softening (i.e.…”

“…In the final stage of the resistance welding process, either mechanical collapse of the joint or loss of material due to expulsion causes shortening of the current path, causing a second reduction in bulk resistance. [20][21][22] The conventional stages of sheet to sheet resistance welding mentioned above were found to be similar for this dissimilar crossed wire RMW process. Typical electrode displacement and dynamic wire to wire resistance measurements for welds made with a current of 200 A and electrode forces of 1 and 5 kgf are provided in Fig.…”

Feasibility study of resistance spot welding of dissimilar Al/Mg combinations with Ni based interlayers

“…In general, contact resistance follows the volume resistivity of the metals involved. 25,26 Magnesium alloy AZ-31B has greater electrical resistivity (92 nV m) than aluminium alloy 5754 (49 nV m), which would lead to increased heat generation and a larger melted zone in the magnesium sheet. 27,28 In addition, greater heat losses will be expected in the aluminium sheet due to the higher thermal conductivity of aluminium 5754 alloy (which is 147 W m 21 K 21 ) compared to magnesium AZ-31B alloy (reported to be 96 W m 21 K 21 ).…”