Effect of Iron Content on Crystallization and Microstructure of EN AC-42000 Alloy

The paper presents research on evaluating the crystallization of Al-Si alloys with increased iron content and analysis of the associated phase transformations. This problem is significant with the growing importance of recycling aluminum alloys, which is justified economically and ecologically. The study concerns the cooling curves of EN AC-42000 alloy (EN AC-AlSi7Mg), into which iron (in the form of Al-Fe mortar - as a substitute for circulating scrap) was introduced with a content of 0.5 to 1.5wt.%. Analysis of crystallization by ATD and microstructure studies of eleven Al-Si-Mg alloys with varying iron content showed up to about 0.4 wt.% Fe, the iron phases formed do not significantly affect the microstructure. They enter into multiphase eutectics of the type α(Al)+(Mg2Si,Fe)+β(Si) or α(Al)+(AlXFeYSiZ)+β(Si), which crystallize after the formation of the double eutectic α(Al)+β(Si). In the range of about 0.5 to 0.9 wt.% Fe, there is a preneutic crystallization of iron phases, mainly the lamellar-neutectic β-Al5FeSi. At more than 1.0 wt.% Fe, the morphology of this phase becomes even more unfavorable (due to primary crystallization) and is accompanied by numerous clusters of shrinkage porosity.