Effect of cooling rate on structure and creep behavior of Sn-0.7Cu-0.5Zn lead-free solder alloy

Metal Physics Lab., Department of Solid State Physics, National Research Center, 12622 Dokki, Giza, Egypt

Corresponding author: gouda.el73@yahoo.com

Received: 27 March 2009
Accepted: 2 June 2009
Published online: 17 September 2009

Abstract

The influence of cooling rate on the structure, melting, hardness and indentation creep behavior of the Sn-0.7Cu-0.5Zn lead-free solder alloy has been studied by XRD, DSC and Vickers microhardness tester, respectively. The study was carried out for the alloy prepared at two different cooling rates of 3.5 °C/s and 11.7 × 10⁻³ °C/s. The results showed that the cooling rate significantly affects the structure, melting and mechanical properties of this alloy. Cu atoms are restricted in the formation of the intermetallic compound (IMC) Cu₆Sn₅ embedded in Sn-matrix in the slow cooled sample. Cu₃Sn compound was detected in the fast cooled sample. The Zn-phase has not been detected by the X-ray diffraction analysis, which means a complete solubility of Zn in Sn-matrix has been obtained. The crystallite size of the Sn-matrix phase in the slow cooled sample was found to be 54.4 nm, while the value of the fast cooled sample was found to be 48.5 nm. This means the fast cooling condition caused grain refinement. This refinement leads to decrease the melting point from 222.7 to 221.2 °C and increase microhardness from 16.4 to 18.2 kg/mm². Furthermore, fast cooling condition improved the creep resistance of Sn-0.7Cu-0.5Zn alloy than that of the slow cooling condition.