Effect of Si additions on the microstructure and properties of Cu-Cr-Mg alloy

Trace Si additions contribute to improve the mechanical properties of Cu-Cr-Mg alloys. The effect of different Si contents (0, 0.06, and 0.16 wt%) on the microstructure, mechanical, and electrical properties of Cu-0.3Cr-0.2 Mg (wt.%) alloys was studied experimentally. It is found that the peak-aged with 0.06 wt% Si alloy exhibits the highest hardness and strength, mainly due to the moderate refinement of FCC-Cr precipitates by Si addition. However, excessive Si addition (0.16Si) results in the formation of Cr₃Si phase, which consumes Cr elements, reducing FCC-Cr precipitation and hence degenerates precipitate strengthening. Results further suggest that the electrical conductivity decreases with increasing Si content due to the increased electron scattering. Thermodynamic calculation reveals that the nucleation driving force of Cr₃Si is an order of magnitude smaller than the transformation energy from FCC-Cr to BCC-Cr, suggesting the nucleation of Cr₃Si probably precedes the transformation of FCC-Cr to BCC-Cr and thereby facilitates the stabilization of FCC-Cr precipitates. This work provides an insight on understanding microstructural/property evolution of Cu-Cr-Mg-Si alloy and designing high-strength Cu-Cr-Mg alloys through Si addition.