Enhancing the mechanical properties of Mg-Zn-Al-Cu-Mn alloy via MgCO3 inoculation treatment: Experimental studies and first-principles calculations

In this work, the low-cost Mg-10Zn-1Al-0.5Cu-0.3Mn without or with the addition of MgCO3 (labeled as S1 and S2 alloys) was successfully fabricated by a rapid-setting water-cooling method. The average grain size of the as-cast alloy decreased from 38.5 to 22.5 µm with the addition of MgCO3. S2 alloy possessed excellent ultimate tensile strength and elongation of 275.6 MPa and 17.5 % in the solid solution state, which were approximately 21.6 and 82.3 % higher than those of the S1 alloy. The transmission electron microscopy results showed that the MnAl2O4 phase with a high melting point was formed in the melt of S1 alloy by adding 1 wt. % MgCO3, which had a phase relationship of (101)Mg||(311)MnAl2O4. Additionally, the results of edge-to-edge matching model showed that the MnAl2O4 phase tended to grow on the Mg matrix phase. The results of the first-principles calculations exhibited that the (101)Mg||(311)MnAl2O4 interface with MnO terminations was a strong interface. The MnAl2O4 phase could be regarded as heterogeneous nucleation points to improve the nucleation rate and thus to refine the grain and enhance the strength. This study can vigorously provide a certain guide for the grain refinement of Mg-Zn based alloys containing Mn.