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

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 [ 1100]_π∥[ 111]_β and ( 1 10)_β∥( 12 10)_π . 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.