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Effect of Si on the brazability and microstructure of Al-40Zn-xSi filler metal was studied, the microstructure and the mechanical properties of the joints which brazed with Al-40Zn-xSi filler metal were investigated respectively. The results indicate that the Al-40Zn-xSi filler metal presents the best wettability on 6061 aluminum alloy when Si content is at 4.0 wt. %. The microstructure of the filler metal indicates that the primary silicon particles could be found when the silicon content exceeds 4.0 wt. %. Al-Si eutectic, mixed with Zn-Al eutectoid, locate at α-Al interdendritic regions in the brazing seam after cooled with water. Moreover, the Al-40Zn-4Si joint possesses the optimum shear strength at 142.28 MPa. However, excess Si would increase the amount of brittle eutectic structures and primary silicon particles in the brazed joints, and thereby decrease the mechanical properties.