Effect of solution time on the microstructure, precipitation behavior and mechanical properties of (Co0.5NiFeCrTi0.5 + SiC)p/7075Al hybrid composite

Abstract

The effect of solution time on the aging behavior, corresponding microstructure and mechanical properties of the (Co0.5NiFeCrTi0.5 + SiC)p/7075Al hybrid composite was systematically studied. The hybrid composite was fabricated via squeeze casting, followed by solution treated for 1, 2, 4 and 6 h and subsequent artificial aging. Microstructural analysis revealed that the solution time had a significant effect on the second phase, HEA/Al interface, precipitation behavior and grains in the Co0.5NiFeCrTi0.5 high-entropy alloy (HEA) particle. The amount of the second phase dissolving into the Al matrix initially increased with the increase of solution time. However, there was no obvious change in the amount of the second phase after 4 h because only the insoluble Al7Cu2Fe phase was left in the matrix. The interface between the Al matrix and SiC particles in the hybrid Al matrix composites did not show significant changes with increasing solution time, whereas the interface between the Al matrix and HEA particles gradually grew. The peak-aged time of composites during artificial aging was gradually shortened with the increase of solution time, indicating that longer solution time could accelerate the precipitation kinetics. Composites solution treated for 2 and 4 h displayed the larger supersaturation of Mg and Zn atoms along with a higher density of precipitates than that of the AMC-1h composite at the peak-aged period. The peak-aged composite solution treated for 2 h showed the highest yield strength and tensile strength (551 and 652 MPa), followed by the composite solution treated for 1 h (495 and 608 MPa) and 4 h (469 and 551 MPa). However, the ductility gradually decreased with the increase of solution time due to the interface reaction between the Al matrix and SiC particles. The relationship between the solution time and precipitation behaviors in the vicinity of the SiC/Al and HEA/Al interface of hybrid composites were systematically studied. Our work provides new insights for the development of heat-treatable Al matrix composites reinforced by metallic particles.