Effect of Al and Bi addition on the corrosion behaviour, hardness, and melting temperature of lead-free solder alloys

Herein, the influence of alloying bismuth (Bi) and aluminum (Al) on the corrosion performance of Sn-9Zn in a 3.5 % NaCl solution was examined. Electrochemical techniques were used to examine the corrosion behaviour of Sn-9Zn, Sn-9Zn-0.5Bi, and Sn-9Zn-0.5Bi-0.5Al. After corrosion measurements, the alloy surfaces were studied by scanning electron microscopy (SEM) and energy dispersive X-ray diffraction (EDX). The results demonstrated that the presence of Bi increased the corrosion resistance because it formed an anodic barrier on the Sn-9Zn-0.5Bi alloy surface. The study extended to measure the Vickers hardness number of these alloys, and the results indicated a significant improvement in the hardness number of the Sn-9Zn alloy by approximately 11 % with Bi and 54 % with Bi and Al. More investigations of the melting temperature behaviour of solder alloys using differential scanning calorimetry (DSC) were also carried out before corrosion measurements. The DSC results demonstrated that Sn-9Zn-0.5Bi-0.5Al had a lower melting temperature than Sn-9Zn and Sn-9Zn-0.5Bi. Therefore, Al and Bi addition improved the melting temperature characteristics of the Sn-9Zn solder alloy. This confirmed that the presence of Bi only enhanced the corrosion resistance, and the presence of both Bi and Al played a crucial role in the properties enhancement of the Sn-9Zn alloy. Consequently, these improved characteristics and properties make the suggested compositions a significant alternative choice to Sn-Pb alloys.