On the basis of Al-Mg-Si（6XXX）system alloy

the effects of w（Mg）/w（Si）ratio on microstructure

thermal conductivity and mechanical properties of the alloy were investigated by permanent mold casting.The results indicate that the primary phase is also changed with the change of w（Mg）/w（Si）.When the w（Mg）/w（Si）is less than 1.53

the phase composition in the alloy is mainly composed of eutectic Si、α-Al andβ-Mg

2

Si phase.When the w（Mg）/w（Si）is equal to 1.53

theθ-Al

2

Cu phase gradually appears in the alloy and the eutectic Si phase disappears.When the w（Mg）/w（Si）is greater than 1.53

the newS-Al

2

CuMg phase appears in the alloy

while theθphase is gradually decreased and finally disappears.The thermal conductivity of the alloy is 175.5 W/（m·K）

when the w（Mg）/w（Si）is 1.53.In addition

the optimal tensile strength and hardness are 153 MPa and 109.14HV and the elongation is 6.54%

respectively.