Microstructure refinement and enhanced tensile properties of Al-11Mg2Si alloy modified by erbium

Abstract The microstructure and tensile properties of the hypoeutectic Al-11Mg2Si alloy modified by the rare earth element erbium was comprehensively studied. It was found that addition of 0.1 wt% Er was efficient for modifying eutectic Mg2Si from coarse mazelike lamellar to fine coralline fiber with a decrease in aspect ratio of Mg2Si from 14.9 ± 2.3 µm to 1.2 ± 0.5 µm and a reduction in interlamellar spacing of eutectic Mg2Si from 2.7 ± 0.5 µm to 0.4 ± 0.2 µm. Furthermore, the eutectic grain transformed from columnar to equiaxial structure with an average size decrease from 41.2 ± 6.1 µm to 9.6 ± 2.5 µm. The excellent modification effect was attributed to the fact that the Er distribution produces undercooling and inhibits the growth of eutectic Mg2Si and grains. The tensile deformation results indicated that trace Er can effectively enhance the strength and the plastic deformation capability of the as-cast hypoeutectic Al-11Mg2Si alloy, especially a tremendously increase in elongation from to from 3.9 ± 0.3% to 12.6 ± 0.7%. The fracture mode changes from brittle mode with a smooth cleavage surface to ductile mode with dense dimples.