Effects of Fe Content on Microstructure and Properties of Secondary Al-Si Alloys

The effects of Fe content on the microstructure and properties of secondar Al-Si alloys were investigated by optical microscope, XRD and universal tensile testing machine, and quantitative analysis of the iron-rich phase morphology in the alloy.The results show that with the Fe content increasing from 0.796%to 1.301%, the secondary dendrite arm spacing in the alloy decreases, then increases and then decreases again.The morphology evolution sequence of iron-rich phase is as follows:compact Chinese script, Chinese script& fishbone-like, Chinese script & fishbone-like & needle-like, needle-like & Chinese script, needle-like; the area fraction of Fe-rich phase gradually increases and the length of Fe-rich phase grows, especially when the Fe content is in the range of 1.022%-1.301%, the length of needle-like β-Fe phase increases significantly, with the longest average length up to 119.5 μm; the appearance of β-Fe phase leads to a sharp decrease in the mechanical properties of the alloy.When Fe content increases to 1.301%, the tensile strength and elongation of the alloy decrease by 26.26%and 52.58%, respectively, compared with that of 0.796%Fe.