Effect of Al-Si-Cu-Ni Brazing Alloy Composition and Brazing Temperature on Properties of High Silica Aluminum Alloy/Kovar Alloy Brazed Joints

Al-7.5Si-23Cu-xNi (x = 0, 0.5, 1.0, 1.5, 2.0, 2.5, mass fraction/%) foil brazing alloys were prepared by melt spinning technology. The effect of Ni content on the microstructure and properties the brazing alloy was analyzed. Vacuum brazing was conducted on CE11 high silicon aluminum alloy and 4J29 Kovar alloy by using the brazing alloy with the best properties, and the effect of brazing temperature (560–600 ℃) on the microstructure, shear strength and air tightness of the joint was discussed. The results show that with the increase of Ni content, the change of liquid/solid phase lines of the brazing alloy was small, the fusion temperature zone was stable, the local eutectic structure of the as-cast brazing alloy increased, and the columnar crystals became coarse. With the increase of Ni content, the fracture strain of the as-cast brazing alloy and the shear strength of the joint first increased and then decreased. When the Ni mass fraction was 2.0%, the brazing alloy had the smallest fusion temperature zone, the lowest melting point, uniform microstructures, more diffusely distributed eutectic phases, and the best toughness and welding performance. When the brazing temperature was lower than 570 ℃, the Al-7.5Si-23Cu-2.0Ni brazing alloy could not melt completely and the combination with base metal was poor. When the brazing temperature was higher than 570 ℃, the element diffusion between the brazing alloy and the base metal was intense, resulting in silicon phase aggregation, and cracks appeared in the weld. With the increase of brazing temperature, the shear strength of the joint first increased and then decreased, and the leakage after welding first decreased and then increased. The best brazing temperature was 570 ℃, at this time the weld was tightly combined with the base metals on both sides, the elements diffused uniformly, and the joint had the largest shear strength and the best air tightness.