Study of the effect of Zn addition on the near eutectic Sn-Ag solder alloy by means of steady state creep measurements and x-ray investigations

The materials used in the present study are Sn-3.3 wt % Ag and Sn-3.3 wt % Ag 1 wt % Zn alloys. Effects of ageing temperature, Ta, ageing time, ta, and stress, σ, on the creep resistance of the alloys under investigation had been studied. Creep tests were performed at room temperature (300 K) under the effect of different stresses ranging from 8.8 to 14.2 MPa on specimens pre-aged at the ageing temperatures 353, 373, 393, and 413 K. At each ageing temperature the specimens were heated for different periods of times 1, 20 and 50 h. The creep behaviour of the present alloys was found to follow a stress power law with exponent n. This exponent was found to be dependent on the temperature and time of ageing. The addition of 1 wt % Zn to the binary lead- free solder Sn-3.3 wt % Ag alloy affected its creep behaviour. It was found to suppress the formation of the β-Sn dendrites leading to refine, stabilize and lead to a uniform distribution of the Ag3Sn particles through the Sn-matrix leading to increase of the creep resistance of the binary lead- free solder alloy. Increasing Ta and Ta lowered the creep strength of both free- and Zn- containing solder alloys. Microstructural changes were investigated by optical, electron microscopy and X-ray diffraction measurements