Effect of a calcium as a modifier in hypoeutectic aluminum-silicon alloys

Modification of the eutectic silicon in Al-Si alloys is traditionally performed by sodium and strontium addition. Although not traditionally used as a modifier, calcium also has the potential to modify the eutectic silicon in Al-Si alloys. Metallographic observation and thermal analysis studies in A357 alloy indicate that. when the cooling rate is quite low. Ca modifies the eutectic silicon. but the effect of Ca as a modifier is not as strong as is Na or Sr. When the cooling rate is high, a fully modified structure can be obtained with calcium. Recovery of Ca in the melt is high and certain. It does not fade with long holding times. Moreover, a premodified ingot can be used, and even when such all ingot is remelted repeatedly there is no calcium loss.; Calcium does increase porosity in castings. In general modification treatment with Ca improves mechanical properties, especially elongation.; Calcium adversely interacts with strontium and reduces the ability of strontium as a modifier. Microstructural and thermal analysis studies show that Ca has a deleterious effect on Sr-modified castings and vice versa. (Abstract shortened by UMI.)...