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

Highlights: • The eutectic Mg₂Si in hypoeutectic Al-11Mg₂Si alloys were modified by Er addition. • The ultimate strength and elongation of hypoeutectic Al-11Mg₂Si alloys with Er addition was significantly improved. • The eutectic grain growing is restrained by the Er distribution and the corresponding component undercooling in front of the grain boundary. -- 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.