Effect Of Fe On The Properties Of A356 Alloy

As typical cast Al-Si alloy, A356 alloys have been certainly used in the fields of automobile manufactory. Fe as one of the most important harmful impurity elements in Al-Si alloy has a huge damage on the mechanical properties of A356 alloy. Most previous researches have been focused on the impacts of Fe on mechanical properties of A356 alloys when ωFe≥0.5wt. %, however, studies about the condition of A356(ωFe<0.5wt. %) are comparatively rare.Our study is focused on the effects of Fe on A356 alloys when ωFe<0.5wt. %. The A356 alloy containing 0.06 wt. % of Fe was added with Al-10 Fe to produce A356 alloys. The OM and SEM were used to investigate the microstructure of A356 alloys, so the effects of Fe addition on the microstructure of A356 alloy can be found out. The mechanism about the effects of Fe on mechanical properties of A356 alloy was revealed by mechanical property test. The microstructure of tensile fracture surface of A356 alloy were observed and analyzed by SEM. In addition, differen amounts of Al-8Mn were added to improve the iron-riched phase morphology of A356 alloys.The results show that there are two stages in the forming process of iron-riched phase as the increase of Fe content. In the beginning, rod iron-riched phase mainly comes into being in A356 alloy when ωFe<0.3wt. %. With the increase of Fe content, the rod iron-riched phase is transformed into needle-like β-Fe phase which is harmful to the properties of A356 alloy. The properties of A356 alloy is impacted by iron-riched phase. With the increase of Fe content, the tensile strength decline steadily and then drop sharply, however, the elongation first drop sharply and then decline steadily. The fracture mode of the alloy also changed from the ductile-brittle fracture which is dominated by ductile fracture to the ductile-brittle fracture which is dominated by brittle fracture.The form of iron-riched phase can be significantly improved by adding Mn. Mn element can transform needle-like β-Fe phase into rod, block or bone-shaped α-Al(Mn,Fe)Si phase. The effect of the transform is more obvious when more Fe and Mn exist. The mechanical properties have been improved due to the improvement of β-Fe phase. The improvement is more obvious as the increase of Fe content. The excessive adding of Mn contributes to the forming of thick herringbone α-Al(Mn,Fe)Si phase, which is unfavorable to mechanical properties. The mechanical properties of A356-x Fe-y Mn alloys do not improved obviously because the fracture mechanisms can not be changed by adding Mn.