Microstructural characteristics and mechanical performances of Al-Si-Cu-Mg-(Ge) alloys prepared under 5GPa-level pressure

The influence of 5 GPa-level high pressure on the microstructure and mechanical properties of Al-7Si-3Cu-0.4 Mg and Al-7Si-3Cu-0.4Mg-0.5Ge alloys is investigated. It is found that alpha-Al dendrites disappear owing to the enhanced growth interfacial stability induced by high pressure. Unconventional nanocrystalline eutectics emerge in the intragranular region, while Si phases in all forms of eutectics display significantly modified structures. The pressure-induced influence on the microstructure evolution of alloy is further explored concerning thermodynamics and kinetics changes. After the direct aging treatment, fine Si particles precipitate densely and uniformly along the <100>Al directions in the Al matrix in both alloys. The APT analysis shows that these Si precipitates are enriched with Mg and segregated by Cu. The role of enhanced solid solubility and solute interactive effect on the formation of nanoscale Si rods is demonstrated. The Al-7Si-3Cu-0.4 Mg alloy fabricated under 5 GPa exhibits the highest compressive strength of 863.6 MPa and microhardness of 214.3 HV after aging. The findings reported in this paper provide a potential way to develop aluminum-silicon-based alloys with improved performance by introducing high pressure.