1999 年 17 巻 3 号 p. 420-425
In order to produce a vaporizing combustion chamber instead of brazing, laser welding was applied to the joint between SUS304 and brass, since it is now fabricated by brazing after many complicated processes.
Materials used in the laser welding were 0.6 mm thick Cu-30%Zn alloy (brass) and 0.5 mm thick austenitic stainless steel SUS304. Stainless steel was lap-welded to Cu-Zn alloy.
As a result of leak test under 0.4 MPa pressure, many leaks were recognized in the weld bead. The observation by means of EPMA and microscopy indicated that the leaks were caused by cracks which resulted from liquid-metal embrittlement of the brass or solidification cracking at grain boundaries of the stainless steel. The number of the cracks increased with increasing in the volume of melted Cu-Zn alloy, and when the volume was lower than 3 vol.% of the melted SUS304, few cracks occurred. Therefore, to eliminate the cracks by re-melting of only the surface of the stainless steel was conducted with the laser beam after the welding. By the elimination process, the cracks were eliminated completely ; consequently, no leakage was recognized except the welding conditions under which many cracks occurred in the weld beads.