Microstructure evolution and rheological properties of Al–Si alloy with high rheological stability fabricated by liquid phase reaction sintering

This study developed a method for preparing a semi-solid Al - 6 Si alloy with high rheological stability, solved the problem of extremely unstable rheological properties of semi-solid alloys prepared by traditional methods, verified its feasibility of direct thixoforming during liquid phase reaction sintering by designing isothermal compression test, explored the evolution law of microstructure and its influence on rheological properties, and obtained the optimal thixoforming conditions. Temperature affects the microstructure evolution pattern of semi-solid alloys mainly by influencing their liquid phase content, which in turn affects their rheological properties. Under low liquid phase content, the semi-solid Al - 6 wt %Si alloy mainly undergoes deformation through plastic deformation mechanism, which has high deformation resistance and causes microstructural evolution instability, leading to instability defects. After the liquid phase content reaches 13.8 %, it can coordinate Al grain to undergo a stable slip, ensuring the steady-state evolution of microstructure and providing necessary conditions for steady-state rheology. Benefiting from the uniform microstructure and highly spheroidized Al grains prepared by liquid phase reaction sintering, the semi-solid billet exhibits low and non-fluctuating stress during the rheological process, demonstrating high steady-state rheological properties. This also indicates that the direct thixoforming of the semi-solid Al-6wt%Si alloy is feasible during liquid-phase reaction sintering. Meanwhile, the semi-solid Al-6wt%Si alloy exhibits shear thinning behavior, and its apparent viscosity decreases with increasing strain rate, which meets the requirements of high strain rate and low flow viscosity for thixoforming. This further proves that the liquid phase reaction sintering method has significant advantages in preparing high rheological stability semi-solid alloys.