The effect of grain refinement and silicon content on grain formation in hypoeutectic Al-Si alloys

The effect of increasing the amount of added grain refiner on grain size an d morphology has been investigated for a range of hypoeutectic Al-Si alloys . The results show a transition in grain size at a silicon concentration of about 3 wt% in unrefined alloys; the grain size decreasing with silicon co ntent before the transition, and increasing beyond the transition point. A change in morphology also occurs with increased silicon content. The additi on of grain refiner leads to greater refinement for silicon contents below the transition point than for those contents above the transition point, wh ile the transition point seems to remain unchanged. The slope of the grain size versus silicon content curve after the transition seems to be unaffect ed by the degree of grain refinement. The results are related to the compet itive processes of nucleation and constitutional effects during growth and their impact on nucleation kinetics. (C) 1999 Elsevier Science S.A. All rig hts reserved.