Effect of La content on microstructure evolution of 20Ag–Cu–Zn–Sn–P–La filler metals and properties of joints

Abstract

The influence of La content on the microstructure evolution of 20Ag–Cu–Zn–Sn–P (wt-%) filler metals and the mechanical properties of joint was investigated in this study. The typical microstructure of filler metal was analysed by means of scanning electron microscopy, optical microscopy and X-ray diffraction. Microstructural observation indicated that the growth of crystal grains in filler metals was prohibited with increasing the La content. It was found that 0·1–0·3 wt-%La improved the wettability of filler metals on 321 stainless steel and Cu substrates. From mechanical properties tests, the shear strength increased with increasing the La content in the range of 0·1 to 0·5 wt-%. When the La content reached 0·5 wt-%, the maximum of the joint shear strength was achieved. When the content is proper, the La addition had a positive effect on wettability by reducing surface tension of liquid alloys.