Effect of different Mg contents on microstructure,tensile properties and fracture behavior of hypoeutectic Al-Mg-Si alloy containing 10 mass％Mg2Si was studied.The results show that adding 1.2-2.8 mass％Mg to the alloy can reduce the size of primary α-Al dendrites.The appropriate amount of Mg significantly refines the Mg2Si eutectic phase in the alloy,and transforms its morphology from coarse Chinese character like to short strip like,granular and fibrous.The refinement of eutectic Mg2Si is attributed to the enrichment of Mg atomic clusters on its both sides,which inhibits the growth of eutectic Mg2Si and promotes a change in its growth direction.The addition of an appropriate amount of Mg simultaneously improves the strength and plasticity of the alloy.The tensile properties of the alloy with 2.8 mass％Mg addition reach the highest,the tensile strength,yield strength and elongation increase from 232.4 MPa,150.4 MPa and 1.5％without Mg addition to 322.0 MPa,270.4 MPa and 6.1％,respectively,with an increase of 38.6％,79.8％and 306.7％,respectively.The fracture mechanism of the alloy without Mg addition is brittle fracture,while the fracture mechanism of the alloy with 2.8 mass％Mg addition changes to ductile fracture.
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