Effects of brazing temperature and post weld heat treatment on 7075 alloy brazed joints

The microstructural evolution and mechanical properties of brazed joints were evaluated before and after the post weld heat treatment. The microstructure and shear strength of brazed joints were improved with the brazing temperature increased, and the highest shear strength of 42 MPa was obtained when brazed at 600 °C. The coarse grains were presented in the joints brazed at the higher brazing temperature, which deteriorated the shear strength dramatically. Post weld heat treatment which including solution treatment and retrogression and re-aging treatment were performed to improve the microstructure and mechanical properties of brazed joints. Through the solution treatment, the brittle intermetallic compounds were reduced significantly and the recrystallization occurred in brazed joints. The coarse lath grains were transformed to the fine grains. After the solution treatment, the retrogression and re-aging treatment were performed and the precipitates which continuously distributed along the grain boundaries were dissolved into the aluminum matrix gradually with the retrogression temperature increased. The fine precipitates were uniformly distributed within the grains and discontinuously distributed on the grain boundaries. When the retrogression temperature was 200 °C, the highest shear strength of 108 MPa was obtained which increased by 160% compared to the shear strength of the brazed joints without post weld heat treatment.