Effect of the Bi content on the mechanical properties of a Sn-Zn-Al-Bi solder alloy

Because of environmental and health concerns, some alternative solder alloys, named lead-free ones, are being developed. Among them, the Sn-Zn-Al system has been studied and reveals promising properties. Selection of the solder alloys, for the electronic industry applications, is conditioned by their mechanical properties due to the stress produced in service. The studied alloys were produced by melting the pure elements in a resistance furnace, under inert atmosphere, and pouring in a steel mould. The samples were heat treated for homogenization of the microstructure. The produced alloys were analyzed by XRF spectrometry and Scanning Electronic Microscopy (SEM/EDS) for chemical and microstructural characterization. In this work the presence of bismuth, in the range of 0-7 weight %, was evaluated in what concerns to the as-cast and homogenized microstructures and mechanical properties. The mechanical properties of the produced alloys, in the as-cast and homogenized conditions, have been determined by tensile strength and hardness tests. The results obtained showed that bismuth has an important effect on the mechanical behavior of the alloys, namely, in the transition from ductile to brittle behavior. This behavior was correlated with the samples microstructures.