Study on microstructure and properties of indirectly brazed joint of Al₂O₃ ceramic/AlSiMg/1A95 aluminum alloy

The joint of 1 A95 aluminum alloy with Al₂O₃ ceramic that was coated with Ni after Mo-Mn superficial treatment was vacuum brazed with Al-Si-Mg solder alloy. The influences of brazing temperature and holding time on the microstructures and shear properties of brazed joint were studied,and the microstructures and fracture morphology of the joint were analyzed. The results show that the shear strength of the joint reaches to maximum value of 74 MPa at the brazing temperature 580 ℃ and holding time of 20 min. Under the optimized condition,the microstructures of the joint are Al₂O₃/Mo-Mn/Al₃ Ni/α-Al/1 A95. With the brazing temperature increasing,the thickness of Al₃ Ni compound at the interface increases. Moreover,with the holding time prolonging,the Al₁₂ Mo compound forms at the interface and covers above the pre-formed Al₃ Ni compound. The fracture mode of the joints is brittle fracture for all the cases. When the brazing temperature is relatively low and the holding time is relatively short,the fracture occurs mainly near the interface between the aluminum alloy and the brazing alloy. Under the optimum process,the fracture occurs both in the reaction zone of the brazing alloy/nickel plated layer,and near the interfacial zone between the aluminum alloy and brazing alloy. If the brazing temperature or holding time is further elevated,the fracture occurs mainly in the reaction zone of the brazing alloy and nickel plated layer.