Synergistic Effect of Sc and Excess Mg on the Microstructure and Mechanical Properties of Hypoeutectic Al-10Mg₂Si Alloy

The effects of Sc and/or excess Mg on the microstructure characteristics, tensile properties, and fracture behavior of a hypoeutectic Al-10Mg₂Si alloy were systematically studied. The results showed that adding 0.25% Sc to Al-10Mg₂Si alloy changed the morphology of the primary α-Al crystals from a coarse dendritic shape to a nearly spherical shape, while the its crystal size is greatly reduced; an additional 2.8% Mg made the the primary α-Al be finer and more uniform. The joint addition of 0.25% Sc and 2.8% Mg greatly reduced the size of Mg₂Si eutectic phase in Al-10Mg₂Si alloy and transformed its morphology from coarse Chinese characters to particles or dots. The refinement of eutectic Mg₂Si can be attributed to the enrichment and adsorption of Sc and Mg atoms on the surface and surrounding of eutectic Mg₂Si, which inhibits the growth of eutectic Mg₂Si and promotes a change in its growth direction. The strength and plasticity of the alloy were simultaneously improved due to the addition of Sc or/and Mg. The YS, UTS, and EL of the alloy with 0.25% Sc and 2.8% Mg added together displayed the highest values of 345 MPa, 145 MPa, and 8.6%, respectively which were 48.7, 40.8, and 230.8% higher than those of the alloy without adding 0.25% Sc and 2.8% Mg, respectively. The brittleness of Al-10Mg₂Si comes from the decohesion of coarse eutectic Mg₂Si particles in the early stage of stretching, while the large amount of plastic deformation generated before cracking of fine eutectic Mg₂Si particles is responsible for the high strength and ductility of the Al-10Mg₂Si-0.25Sc-2.8 Mg alloy.