Effect of Ag addition on the creep characteristics of Sn–8.8 wt%Zn solder alloy

Abstract

Full implementation of the new generation of lead-free solders requires detailed knowledge and understanding of their mechanical behavior. The materials used in the present study are Sn–8.8 wt%Zn (binary) and Sn–8.8 wt%Zn–1.5 wt%Ag (tertiary) alloys. Effect of Ag addition, deformation temperature T and the applied stress, σ, on the creep characteristics have been studied. Creep tests were performed under the effect of different stresses ranged from 17.8 to 26 MPa at the deformation temperatures 291, 303, 323 and 343 K. The transient creep parameters β and n were found to be markedly affected by the creep test conditions, T and σ. The parameter β was found to be decreased by increasing T and/or σ while n was found to increase by increasing T irrespective of the applied stress σ. The steady-state creep rate έ st was found to increase with increasing both T and σ in both solder alloys. The steady-state creep rate έ st was related to the stress σ with the relationship έ st = Cσ m where m = (∂ln έ st/∂ln σ) is the stress exponent. This exponent is decreased with increasing T in both alloys. Addition of 1.5 wt%Ag to the binary alloy increased its creep resistance. This behavior was attributed to the formation of the intermetallic compounds (IMCs) AgZn and Ag 3Sn during solidification. These IMCs played the role of pinning action for the moving dislocations and consequently leading to the increase of its creep resistance. Micro-structural changes were investigated by scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) analysis.