Insight of high-entropy alloy particles-reinforced 2219 Al matrix composites via the ultrasonic casting technology

Abstract The microstructure and mechanical properties of metallic composites can be favorably modified by the introduction of various reinforcing particles. Different contents of high-entropy AlCoCrFeNi alloy particles (HEAps) were individually injected into the 2219 Al alloys via ultrasonic casting technology. Some irregular HEAps were observed along the grain boundaries. They served as reinforcing factors and provided numerous potential heterogeneous nucleation sites on the α-Al matrix. The average grain size of the HEAps-reinforced aluminum matrix composites (HEAps/AMCs) reduced dramatically from 136.08 μm (0 wt%) to 34.95 μm (1.5 wt% HEAps). Several rich-Al, Co, Fe, Cr, Ni, Cu elements with needle-shaped phases accompanied by some distinctive plate-like precipitates were observed in the Al matrix. Additionally, the optimal addition of HEAps was approximately 1.5 wt%, for any excess was detrimental to the microstructure and properties. The HEAps had a substantial influence on the mechanical properties, namely 1.5 wt% corresponding to the optimum tensile strength (217.4 MPa), and 3 wt% ascribing to the maximum micro-hardness (120.5 HV). The primary strengthening mechanisms were explored, revealing the grain refinement, solute, and precipitate strengthening to be the dominant factors. However, ∆σCTE and ∆σEMM showed very limited contribution. Meanwhile, ∆σLoad, ∆σWH1, and ∆σWH2 offered marginal increments to the yield strength. Theoretically, a novel strengthening model was established, and the yield strength of the HEAps/AMCs in an optimal HEAps addition range was effectively predicted.