The precipitation-hardenable aluminum alloy 6061 (AA 6061) is favored for aerospace components and automotive parts. However, the tenacious oxide layer on the surface greatly limits the quality and applicability of joining AA 6061. In this study, the joining method of solid-state diffusion bonding was implemented for AA 6061 plates, and the effects of post-weld heat treatment (PWHT) on the joint interface were investigated. The bonding temperatures were within the range of 500–530 °C, and the time periods varied from 30 to 240 min under a static pressure of 5 MPa in a vacuum. The diffusion bonded specimens were subjected to T4- and T6-PWHT to improve the bonding quality. The interfacial microstructure of the joints was analyzed by scanning electron microscopy, and the mechanical properties were evaluated with shear tests. The experimental results showed that the shear strength of the diffusion bonded joint could reach around 71.2 MPa, which was highly dependent on bonding temperature and holding time, and T6-PWHT further enhanced it to over 100 MPa. The effects of PWHT on the diffusion bonded AA 6061 joint were investigated, and the fractography on the sheared surfaces indicated that PWHT-T6 played an important role in enhancing joint strength, which was consistent with the measured shear strength. The sequential PWHT for AA 6061 after diffusion bonding was proven to be feasible for bonding of AA 6061 parts, and the joint strength was sufficient for industrial needs.

In this study, 2024 aluminum alloy was diffusion bonded to identify the effect of the bonding temperature, applied pressure, and heating time on the microstructure, hardness, and bonding strength. The shear strength increased from 62.5 MPa to 81.2 MPa along with the rise in bonding temperatures from 440 °C to 490 °C. The bonding strength rose from 62.5 MPa to an optimal value of 81.2 MPa by extending the bonding time from 30 min to 240 min at a bonding temperature of 490 °C and a constant pressure of 5 MPa. In addition, various post-weld heat treatments for diffusion-bonded joints were also performed to improve the bond quality. After the T6 or T4 post-weld heat treatment, the hardness at the bonding interface and the substrate increased due to the precipitation of Al₂Cu. Post-weld T4 and T6 heat treatments increased the interface microhardness from 106.3 Hv to 138.25 Hv and 130.6 Hv, respectively. The bonding strength of the AA2024 was significantly improved up to 124.5 MPa and 164.3 MPa by the T4 and T6 heat treatments, respectively.