Investigating the influences of Fe, Mn and Mo additions on the evolution of microstructure and mechanical performances of Al–Si–Mg cast alloys

Abstract

Understanding the evolution of Fe–containing intermetallic compounds (Fe–IMCs) in Al–Si–Mg alloys is essential for improving the mechanical performances. This paper aims to systemically evaluate the influences of both the single addition of Mn or Mo, and the combined additions of Mn and Mo on the evolution of Fe–IMCs and mechanical performances of Al–Si–Mg cast alloys. Results reveal that the as–cast microstructures of these alloys are primarily composed of Al3M (M means Ti, Zr, or TiZr), α–Al, eutectic Si, Mg2Si, Q–Al5Cu2Mg8Si6, and some irregular Fe–IMCs. It is clear that the morphology and size of Fe–IMCs are significantly affected by the single or combined addition of Mn and Mo. Moderate Mn content facilitates the formation of Chinese script–like α–Al(FeMn)Si phases that are favorable to the mechanical properties. The combined addition of Mn and Mo refines the α–Al(FeMn)Si phases and promotes the formation of Chinese script–like α–Al(FeMnMo)Si phases. Furthermore, as the Mo level increases, β–AlFeSi, π–Al8FeMg3Si6, and α–Al(FeMn)Si disappear successively, which also helps improve the mechanical performances. In this article, maximum hardness, ultimate tensile strength, yield strength and elongation of 87.04 HV, 275.34 MPa, 139.70 MPa, 7.88% are obtained when Fe, Mn and Mo are added at 0.20wt.%, 0.02wt.%, and 0.27wt.%, respectively. The purpose of this work is to provide an efficient method to minimize or even eliminate the adverse effects of Fe–IMCs and thus improve the mechanical performances of Al–Si–Mg cast alloys.