Abstract: In order to improve the properties of the brazing alloy Al-7Si-20Cu,a small amount of rare earth(RE) Er was added into Al7Si-20Cu brazing alloy aiming at examining the effect of different amounts of Er on the physical properties,spreading property and mechanical properties of the solders.Results show that a small amount of Er has no obvious effect on the melting temperature of Al-Si-Cu solder alloy,but can notably improve spreading property of brazing alloy on LF21 surface,especially when the content of Er is within 0.05~0.1%.According to the examination on the microstructure of AlSiCu brazing alloy,with the increase of Er content the microstructure becomes finer and the length of acicular eutectic Silicon is shortening.