In case of laser welding of same metals, the mechanical properties of weld show a little difference from that of base metal. This article discribes metallurgical studies on several factors which affect mechanical properties of laser weld. In order to study about rapid thermal hysteresis, the changes of the age hardening curves in various solution treatment and of ageing temperature and time, a difference between fusion zone and base metal using X-ray diffractometer, thermal hysteresis around fusion zone, the change of metal component by evaporation and metallographic structure of fusion zone were examined. Additionally, the studies on the appearance of blowhole and crack, and on the area of heat affected zone were performed.
Ageing curve of Ag-Pd-Cu-Au alloy varied with solution treatment temperature. The fusion zone by laser irradiation was one supersaturated solid solution, while solution treated base metal precipitated into two solid phases. The increase in temperature around the fusion zone was restricted only in very narrow area, and no heat affected zone was found. In fusion zone, silver component was decreased. Crack regarded as stress corroision crack and blow hole appeared in the weld.