Effect of Microstructure Evolution of Iron-Rich Intermetallic Compounds on Mechanical Property of Al–7Si–0.3Mg Casting Alloy with Low Iron Content

Abstract

In this study, the effects of microstructure evolution of iron-rich intermetallic compounds on mechanical properties in Al–7Si–0.3Mg cast alloys with low iron content (0.1 to 0.3 wt pct) were investigated. A series of characterization methods was utilized to observe the microstructure of iron-rich intermetallic compounds. The results indicate that the dominant iron-rich intermetallic compounds change from π-AlMgFeSi phase with a script-like morphology to β-AlFeSi phase with a needle-like morphology as Fe content increased. Besides, the 2D/3D morphology of Fe-rich intermetallic compounds significantly changes with the increase of Fe content. In 0.3 wt pct Fe alloy, the π-AlMgFeSi phase with a layered structure and seaweed-like morphology forms on the surface of the β-AlFeSi phase with a platelet-like morphology, and the crystallographic orientation relationships were $\left[ {1100} \right]_{\pi } \parallel \left[ {111} \right]_{\beta } \,{\text{and}}\,\left( {\overline{1} 10} \right)_{\beta } \parallel \left( {1\overline{2} 10} \right)_{\pi }$. In addition, the β-AlFeSi phase tends to nucleate in 0.2 wt pctFe alloy, while the growth of β-AlFeSi phase is boosted in 0.3 wt pctFe alloy. The sufficient growth of β-AlFeSi phase leads to the formation of the π-AlMgFeSi phase. Furthermore, the formation of the π-AlMgFeSi phase improves the mechanical properties of alloys. The microstructure morphology of π-AlMgFeSi phase formed on the surface of the platelet-like β-AlFeSi phase enhances the adhesive strength between the β-AlFeSi and the matrix and reduces the negative effects of Fe-rich intermetallic compounds on mechanical properties of Al–7Si–0.3Mg cast alloys.