Key Factors Influencing Eutectic Si Modification in Al-Si Hypoeutectic Alloy by Trace La
The modification of eutectic Si to fiber morphology from coarse plate-like morphology is essential for producing an Al-Si hypoeutectic alloy.Furthermore,chemical modification through the addi-tion of modifying elements,such as Na and Sr,to melt is the most widely used method in industrial pro-duction to improve microstructures.Recently,the effect of rare earth metals on the eutectic Si modifica-tion has also attracted considerable attention,especially for the economical element La.Key factors influ-encing eutectic Si modification in Al-Si hypoeutectic alloy by trace La are theoretically explored.The re-sults demonstrate that the solubility of La in the primary α-Al phase and interaction parameter between La and Al(or Si)primarily contribute to the eutectic Si modification.When the addition level of trace La is within its solubility in the primary α-Al phase,La distributes in α-Al and eutectic Si,and the modification ef-fect increases with the La addition level.When the addition level of trace La is greater than its solubility in α-Al,a ternary compound containing Al,Si,and La exists before the eutectic reaction due to the signifi-cant value of the interaction parameter between La and Al(or Si).Calculated results further prove that the composition of the ternary compound is AlSiLa due to the substantial value of heat for the formation of AlSiLa and the small value of interfacial energy between Al melt and AlSiLa.Under this condition,La distributes in α-Al,AlSiLa,and eutectic Si,and the La content in α-Al and eutectic Si almost remain con-stant.Thus,the modification effect almost stays unchanged with La addition.A suitable modification ef-fect is achieved when the La addition level is around its solubility in the primary α-Al phase.
Al-Si hypoeutectic alloymodificationinteraction parametertrace element Lasolubility
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