Process of indirect brazing alumina to 5A05 Al alloy

Vacuum brazing of Al alloy and electroless nickel plated alumina was carried out with Al-Si-Mg brazing alloy and Mg powder in home-made technical hood. Effects of brazing temperature and holding time on the interface structure and shear strength of joints were analyzed. The experimental results show that the interface structure is Al₂O₃/Ni(I zone)/Al₃Ni₂ (II zone)/Al₃Ni+Mg₂Si(III zone)/α(Al)+Mg₂Si(IV zone)/5A05 when the brazing temperature is 570°C and holding time is 15 min. The maximum shear strength of joints is up to 25 MPa. As the holding time prolongs, Ni layer becomes thin, Al₃Ni zone changes little and Al₃Ni+Mg₂Si zone becomes thick and dispersed. When the holding time is 50 min, Al₃Ni+Mg₂Si zone becomes scattered and Mg₂Si near 5A05 alloy disappears. The effect of brazing temperature on the joints is similar to that of holding time. The fracture mode of joints is brittle. When the shear strength of joints is lower, the joints fracture near α(Al)+Mg₂Si on Al alloy side. When the shear strength of joints is higher, the joints fracture on Ni+interface (II zone and III zone).