Variation of microstructure and mechanical properties of hybrid particulates reinforced Al-alloy matrix composites with ultrasonic treatment

Abstract

The effects of ultrasonic treatment (UT) on the microstructure and mechanical properties of 10 wt% Mg2Si+1 wt% nano-sized SiC particles (SiCnp for short) hybrid reinforced Al-Cu alloy matrix composites were investigated for first time. The existence of Mg2Si phase solves the problem effectively that the particle content of SiCnp/Al-Cu composites cannot be high by the external addition of SiCnp and casting method. The results show that after UT, the big eutectic Mg2Si phase was remarkably refined, from coarse Chinese characters (about 50 μm) to fine strips or dots (about 0.5–2 μm). Meanwhile SiCnp agglomerations were also eliminated, and both Mg2Si phase and SiCnp were uniformly distributed in the composites. The interaction between Mg2Si and SiCnp was discussed to analyze this behavior that SiCnp could act as heterogeneous nucleus of Mg2Si phase, or be captured by the Mg2Si solid front during solidification, leading to the refinement of eutectic Mg2Si phase. It was also found that the effects of UT could be even improved by using squeeze casting (SC), instead of gravity casting (GC). The as-cast ultimate tensile strength (UTS) and elongation of hybrid Mg2Si + SiCnp/Al-Cu composites fabricated by combining UT and SC were enhanced to 336 MPa and 3.0%, which were increased by 31.3% and 130.8%, respectively, compared with the composites without UT. The UTS of the hybrid Mg2Si + SiCnp/Al-Cu composites was also 33.5% higher than that of the Al-Cu matrix alloy and 23.5% higher than that of 1 wt% SiCnp/Al-Cu composites prepared by the same process.