Simultaneously enhancing strength and plasticity of age-hardened AlCu alloy induced by bimodal sized ZrB2 particles

A bimodal-sized (micro/nano) ZrB₂ particle-reinforced AlCu alloy was developed via semi-solid stir casting in this study, the age-hardening behavior was investigated and compared with that of single-sized (micro or nano) ZrB₂ particle-reinforced AlCu alloys, and the corresponding mechanisms were discussed. The research results show that bimodal ZrB₂ particles can effectively refine the grain size of AlCu alloys and promote aging precipitation, resulting in a decrease of peak aging time from 18 h to 12 h, and precipitation temperature drops for the θ’ phase in the differential scanning calorimeter curve. More importantly, compared with the AlCu matrix alloy, bimodal-sized (micro/nano) ZrB₂ particles can bring about simultaneous enhancement of strength and plasticity, with its ultimate tensile strength and elongation increasing from 375 MPa and 14.4 % to 416 MPa and 21.6 %, respectively, i.e. with the enhancement ratio of 10.9 % in tensile strength and 50 % in elongation. And bimodal-sized ZrB₂ particle-reinforced AlCu alloy has the highest work hardening rate as well. Meanwhile, it is found higher-density dislocations were generated in the bimodal-sized ZrB₂/Al-Cu alloy, with the geometric necessary dislocation density at aging state increasing from 0.18 × 10¹⁴ m⁻² to 0.42 × 10¹⁴ m⁻². This work adopts a preparation process of semi-solid mechanical stirring, pre dispersion of ZrB₂/Al powder, and auxiliary dispersion of nano-sized particles driven by micro-sized particles. The semi-solid high viscosity aluminum liquid is utilized to inhibit particle sedimentation, achieving more uniform particle dispersion.