ICSR (Soldering and Reliability) Conference Proceedings

The Effects of Bi and Aging on the Microstructure and Mechanical Properties of Sn-Rich Alloys

Authors: André Delhaise, Doug Perovic, and Polina Snugovsky, Ph.D.
Company: University of Toronto and Celestica, Inc.
Date Published: 5/19/2015   Conference: ICSR (Soldering and Reliability)

Abstract: This paper examines the effects of Bi on the microstructure and hardness of Sn-Bi and Sn-Cu-Bi alloys subjected to ageing treatments at room and elevated temperatures. One main concern with SAC alloys that has led to research of Bi-containing alloys is the degradation of mechanical and thermomechanical properties due to the coarsening of microstructure during aging, and in earlier studies, the inclusion of Bi in the alloy results in a uniformity of microstructure and an increase in alloy hardness. The goal of this paper and ongoing research is to investigate whether these trends hold for binary alloys, and to understand what mechanisms are responsible for these effects.

Four alloys – Sn-1Bi, Sn-5Bi, Sn-0.7Cu-1Bi, and Sn-0.7Cu-5Bi - were aged at room temperature for 10 days or 28 days. Two of these, Sn-1Bi and Sn-5Bi, were aged at 100oC for 7 days, and were all cooled in air. The microstructure of the samples after solidification and aging were compared using Scanning Electron Microscopy (SEM). Alloy hardness after solidification and aging was measured using a Rockwell hardness tester HR15X with a ¼” Carbide ball indenter. In alloys containing Bi precipitates, these particles became more uniformly distributed with aging. Hardness was observed to not undergo any significant changes after aging, which differs significantly from SAC alloys.

Key Words: 

Bismuth, Aging, Microstructure, Hardness

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