Improving resistance to softening and strength of Cu-Fe-Mg-P alloy through inhibition of α-Fe phase growth

In this study, a Cu-2.3Fe-0.1Mg-0.03P alloy was developed, and the influences of Mg element on the microstructure and mechanical properties of the alloy were investigated. The Cu-2.3Fe-0.1Mg-0.03P alloy exhibited a softening temperature of 580 °C, a tensile strength of 506 MPa at room temperature and an electrical conductivity of 66.8 % IACS, which were higher than those of the Cu-2.3Fe-0.15Zn-0.03P (C19400), and the softening temperature was increased by ∼ 100 °C. Through transmission electron microscopy (TEM) observations, combined with first-principles calculations and kinetic analyses, it was shown that the addition of Mg element reduced the solubility of Fe in the Cu matrix, thereby promoting the precipitation of Fe atoms, which enhanced the electrical conductivity of the alloy and increased the quantity of α-Fe phases. Furthermore, the incorporation of Mg element diminished the diffusion coefficient of Fe atom within the Cu matrix, consequently reducing the growth rate of α-Fe phase during aging. These two factors collectively enabled the α-Fe phases to maintain a finer, more dispersed distribution at elevated temperature, thereby impeding the recrystallization behavior of the alloy at high temperature, which primarily contributed to enhancements of both resistance to softening and strength of the Cu-Fe-Mg-P alloy.