Grain refining mechanism of Al-3B master alloy on hypoeutectic Al-Si alloys
(1. Key Laboratory for Advanced Materials Processing Technology of Ministry of Education,
Tsinghua University, Beijing 100084, China;
2. Department of Mechanical Engineering, Tsinghua University, Beijing 100084, China)
Tsinghua University, Beijing 100084, China;
2. Department of Mechanical Engineering, Tsinghua University, Beijing 100084, China)
Abstract: Al-3B master alloy is a kind of efficient grain refiner for hypoeutectic Al-Si alloys. Experiments were carried out to evaluate the effect of undissolved AlB2 particles in Al-3B master alloy on the grain refinement of Al-7Si. It is found that the number and the settlement of AlB2 particles in the melt all have effect on the grain refining efficiency. On the basis of experiments and theoretical analysis, a new grain refinement mechanism was proposed to explain the grain refinement action of Al-3B on hypoeutectic Al-Si alloys. The formation of ‘Al-AlB2’ shell structure is the direct reason for grain refinement and the undissolved AlB2 particles is the indirect nucleating base for subsequent α(Al) phase.
Key words: Al-3B master alloy; hypoeutectic Al-Si alloys; nucleation mechanism; grain refinement