Effect of MgO on Phase Selection in Al-Mg-Si-Fe-Mn Alloys

The effect of commercial nano-sized MgO particles on the heterogeneous nucleation of iron-rich intermetallic compounds in Al-5Mg-2Si-0.7Mn-1.1Fe (wt%) was investigated. The experimental results showed that, when solidified under non-equilibrium conditions, the formation of Al-6(Fe, Mn) phase was enhanced by a decreased cooling rate. The MgO addition resulted in a suppression of Al-15(Fe, Mn)(3)Si-2 phase. However, it promoted the heterogeneous nucleation of the Al-6(Fe, Mn) phase. Besides, a peritectic reaction commenced at the liquid/Al-6(Fe, Mn) interface, resulting in the formation of Al-15(Fe, Mn)(3)Si-2 and (Al) at the interface in the alloy solidified at 0.1 K/s. The investigation of the effect of MgO on phase selection included analysis of the crystallographic matching at the interface.