Effect of Heat Treatment on Joint Properties of Laser-Welded Ag-Au-Cu-Pd and Co-Cr Alloys

PURPOSE: This study investigated the effect of heat treatment on the strengths of laser-welded cast Ag-Au-Cu-Pd and Co-Cr alloys. MATERIALS AND METHODS: Cast plates of Ag-Au-Cu-Pd (Ag) and Co-Cr (Co) alloys were prepared. After polishing the surfaces to be welded, the plates were matched and butted Ag to Ag (Ag/Ag), Co to Co (Co/Co), and Ag to Co (Ag/Co) and welded using Nd:YAG laser at a pulse duration of 10 ms, spot diameter of 1 mm, and voltage of 200 V. Five specimens were prepared for each experimental condition by bilaterally welding them with five spots. The Ag/Ag, Ag/Co, and control Ag underwent two heat treatments-softening (ST) and hardening (AH). A group of as-cast specimens serving as controls was not given either heat treatment. The failure load and percent elongation were measured at a crosshead speed of 1.0 mm/min. RESULTS: The fracture resistance of Co/Co was similar to that of the control Co, while the fracture resistance of Co/Ag was significantly lower than that of both like alloy pairings for all heat-treating conditions. The control Ag had greater fracture resistance after AH and lower fracture resistance after ST. The AH treatment increased the fracture resistance, and the ST treatment decreased the fracture resistance of both Ag/Ag and Co/Ag, although not significantly. The percentage of elongation appeared to positively correlate with the fracture resistance results. CONCLUSIONS: The results obtained in this study indicated that the age-hardening heat treatment increased the weld strength between the paired Au-Ag-Cu-Pd alloys and between the Au-Ag-Cu-Pd and Co-Cr alloys.