Abstract: The effects of Si content on the microstructure and mechanical properties of as-cast Al-6.0Mg-xSi alloy were investigated by OM,SEM,hardness test and tensile test.The results show that the microstructure of as-cast Al-6.0Mg alloy without Si consists of α-Al matrix and irregular massive Al₃Mg₂ phase.With the increase of Si content,the number of skeleton-like Mg₂Si phase in as-cast Al-6.0Mg-xSi alloy increases and aggregates and grows up at the grain boundary,the amount of blocky Al₃Mg₂ phase decreases.With the increase of Si content,the strength of as-cast Al-6.0Mg-xSi alloy increases first and then decreases,the hardness increases gradually,and the elongation decreases continuously.The tensile strength and yield strength of the alloy reach 264.8 MPa and 226.3 MPa,respectively,when Si content is 1.6%.