The effect of minor iron additions and aging time on the internal friction, dynamic Young's modulus, and corrosion behavior of Sn-0.7Cu lead-free solder alloy

The aim of the present work is to study the effects of minor addition of Fe (0.2-0.5 wt.%) and thermal aging time on the microstructure, mechanical damping, and corrosion behavior of Sn-0.7Cu eutectic solder alloys. The alloys were solution treated at 150 °C for 3 h and then aged at 100 °C for different time intervals (6-96 h) and quenched in cold water at 2 °C. Phase identification, microstructural dynamic Young's modulus (E) and internal friction (Q -1 ), microhardness (Hv) in the temperature range of 60-100 °C, and electrochemical characterization (OCP, EIS, Tafel polarization) were examined. The calculated stress exponent and activation energy confirm that dislocation climb controlled by core diffusion is the dominant deformation mechanism. Results indicate that adding 0.4 wt. % Fe effectively refines the matrix microstructure and achieves a uniform distribution of FeSn 2 and Cu 6 Sn 5 intermetallic precipitates. These precipitates pin dislocations to restrict defect mobility, thereby decreasing internal friction and increasing the dynamic Young’s modulus. The enhanced corrosion resistance is attributed to improved interfacial electrochemical stability, as evidenced by the electrochemical measurements. Moreover, the fine microstructure is beneficial for enhancing the mechanical integrity and corrosion resistance of the solder alloy.