Abstract: The optical microscope, SEM, electron probe and XRD were used respectively in this research to investigate the dominant mechanism of rare earth Y added in Al-8%Mn alloy melt on microstructure of the alloy. The effect of amount of rare earth Y on the mechanical properties and corrosion resistance of the alloy was analyzed as well. Our results show clearly that the addition of rare earth Y can refine Al₆Mn compounds and α-Al phases in Al-8%Mn alloy during alloy solidification. Moreover, after adding 3wt.% Y to Al-8%Mn alloy melt, the refining efficiency caused by Al₆Mn and α-Al phases is most significant. The morphology of Al₆Mn phases changes from coarse lath to small piece and blocky, and the average size of Al₆Mn reduces from 67.4 μm to 36.5 μm. Hence, the morphology of α-Al phase transfers from coarse columnar crystal to equiaxed crystal, and the average size decreases to 48 μm when 3wt.%Y is added to Al-8%Mn alloy melt. Both the ultimate tensile strength and elongation of Al-8Mn-3wt.%Y alloy are improved up to 141.37 MPa and 2.26% respectively. In the end, the addition of rare earth reduces the intergranular corrosion resistance of the alloy in etching solution (30 g NaCl+10 mL HCl+1 L H₂O).

Key words: Al-Mn alloys, Al₆Mn, α-Al, mechanical properties, corrosion resistance