Effect of post-weld heat treatment on the microstructure and mechanical properties of SSFSW HVDC AlSiMgMnCu alloy

Abstract

The high vacuum die casting (HVDC) AlSiMgMnCu alloy sheets were successfully welded by stationary shoulder friction stir welding (SSFSW) technique, and a post-weld heat treatment (PWHT) was also performed to enhance the mechanical properties of the joints. The microstructure and maximum texture intensity obviously change in different zones before and after the heat treatment. In the as-SSFSW joint, the microstructure in nugget zone (NZ) and thermal mechanically zone (TMAZ) possessed stronger texture of brass components than the heat affect zone (HAZ). After the T6 PWHT, the joints of the alloy showed continuous recrystallization. The texture type is still brass texture in NZ and TMAZ, while the texture intensity in the NZ and TMAZ significant increased. Some grains in NZ and TMAZ rotate 20° towards the <111>. The nano-precipitation β'', Q′ and θ′ phases formed in the Al matrix after the T6 PWHT. The yield strength, ultimate strength and elongation of PWHT joints are 252 MPa, 297 MPa and 4.1%, respectively. The joint welding coefficient of PWHT joint is 96.1%, which was ascribed to dislocation and precipitation strengthening.