Study on microstructure and mechanical properties of Cu/Al joints brazed by flux-cored Al–Si filler metal

This paper aims to study the mechanical properties of Cu/Al joint brazed with flux-cored Al–Si filler metal and reveal the fracture mechanism of the joint. The study describes that the solid-liquid phase line range of the flux-cored Al–Si filler metal is 585–620 °C, the spreading area of the filler metal on the base metal is the largest and the wettability is the best at 600 °C, and the tensile strength of the copper aluminum joint reaches 56 MPa. The microhardness of the brazed joint area of the joint is significantly higher than that of the copper and aluminum base metals, about 4.28 GPa. The microstructure of the joint is mainly Cu9Al4, CuAl2, α-Al, and (Si phases+ α-A1 + CuAl2) eutectic. In which, the crystal zone axis of Cu9Al4 is [0−1 1] and that of CuAl2 is [1 0 3]. In the brazed joint, the joint fracture is between CuAl2 and α-Al, which belongs to a mixed fracture.