Effects of Zn Addition on Dendritic/Cellular Growth, Phase Formation, and Hardness of a Sn–3.5 wt% Ag Solder Alloy

Abstract

Sn–Ag‐based alloys are considered good alternatives to soldering operations as compared with the traditional Sn–Pb solder alloys. Herein, the effects of 0.5 and 1.0 wt% Zn additions to a Sn–3.5 wt% Ag eutectic alloy on cooling and growth rates, microstructure, and microhardness along the length of directionally solidified (DS) castings are examined. Characterization techniques such as optical microscopy (OM), scanning electron microscopy (SEM), X‐ray fluorescence (XRF), X‐ray diffraction (XRD), and Vickers microhardness are used to examine different samples extracted along the length of the DS castings. The Sn–3.5 wt% Ag alloy is shown to have a fully dendritic microstructure, characterized by a Sn‐rich matrix with the eutectic mixture located in the interdendritic regions. On the other hand, the alloy modified with 1 wt% Zn exhibits a microstructure entirely formed by β‐Sn cells, with a mixture of β‐Sn, ε‐Ag3Sn, and ζ‐AgZn phases in the intercellular regions. The DS Sn–3.5 wt% Ag–0.5 wt% Zn alloy casting exhibits a cellular/dendritic transition at a critical cooling rate of 8.5 °C s−1. The 0.5 wt% and 1 wt% Zn additions to the Sn–3.5 wt% Ag alloy improve hardness by 42.6% and 47.5%, respectively.