Deformation behaviour of Sn-3.0Ag-0.5Cu (SAC305) solder wire under varied tensile strain rates

Abstract

Purpose The purpose of this paper is to investigate the relationship between microstructure and varied strain rates towards the mechanical properties and deformation behaviour of Sn-3.0Ag-0.5Cu (SAC305) lead-free solder wire at room temperature. Design/methodology/approach Tensile tests with different strain rates of 1.5 × 10−6, 1.5 × 10−5, 1.5 × 10−4, 1.5 × 10−3, 1.5 × 10−2 and 1.5 × 10−1 s−1 at room temperature of 25°C were carried out on lead-free Sn-3.0Ag-0.5Cu (SAC305) solder wire. Stress-strain curves and mechanical properties such as yield strength, ultimate tensile strength and elongation were determined from the tensile tests. A microstructure analysis was performed by measuring the average grain size and the aspect ratio of the grains. Findings It was observed that higher strain rates showed pronounced dynamic recrystallization on the stress-strain curve. The increase in the strain rates also decreased the grain size of the SAC305 solder wire. It was found that higher strain rates had a pronounced effect on changing the deformation or shape of the grain in a longitudinal direction. An increase in the strain rates increased the tensile strength and ductility of the SAC solder wire. The primary deformation mechanism for strain rates below 1.5 × 10−1 s−1 was grain boundary sliding, whereas the deformation mechanism for strain rates of 1.5 × 10−1 s−1 was diffusional creep. Originality/value Most of the studies regarding the deformation behaviour of lead-free solder usually consider the effect of the elevated temperature. For the current analysis, the effect of the temperature is kept constant at room temperature to analyze the deformation of lead-free solder wire solely because of changes of strain rates, and this is the originality of this paper.

Deformation behavior relationship between tensile and nanoindentation tests of SAC305 lead-free solder wire

“…In addition, through the preliminary study, it was also indicated that the increment of strain rates increased the ductility (Abdullah et al , 2017). Figure 5 shows the variation of ductility toward strain rates for the current analysis and in agreement with the findings from the preliminary study.…”

“…Preliminary study has been conducted and showed that the occurrence of this phenomenon is because of the relationship between the changes of dislocation pile-up or density, adiabatic temperature and grain size of SAC305 solder wire. It was observed through the microstructure analysis of SAC305 solder wire that the increment of the strain rates decrease the grain size (grain refinement) and increase the level of dislocation density (Abdullah et al , 2017). The grain refinement occurs during the dislocation pile-up until the dynamic balance is achieved, and this indicates the initial occurrence of dynamic recovery.…”

“…The dotted red line as shown in Figure 6(b) is the approximate elastic curve that can be further calculated by using Hertzian contact theory (Schuh and Nieh, 2003). Based on the preliminary study (Abdullah et al , 2017), it was noted that SAC305 solder wire that experienced the highest value of strain rate of 1.5 × 10 −1 s −1 has the lowest value of average grain size because of the grain refinement phenomenon. Thus, it can be inferred that the occurrence of earliest initial pop-in and the highest occurrence of pop-in event in the P-h profile can be used to indicate the lowest value of average grain size possessed by SAC solder wire with the highest strain rate.…”

“…From Figure 7, it is seen that the increment of strain rates increases the YS and UTS of SAC305 solder wire. From the preliminary study, it was shown that the increase of YS and UTS of SAC305 solder wire with the increment of strain rates is because of the decreased grain size (grain refinement) and increased dislocation density (Abdullah et al , 2017). Both higher grain refinement and dislocation density are known to hinder the movement grain or microstructure of SAC305 solder wire; this directly increase the value of YS and UTS which is based on the Hall–Petch relation (Deghaid Pereira et al , 2013; Tsao et al , 2012).…”

“…The m value can be calculated from the slope of the log–log relation of true stress and true strain, while C is the strength coefficient and can be measured from the intercept of the log–log relation of true stress and true strain. The n value can be measured using the following relation (Abdullah et al , 2017): …”