Surface pretreatment of 6063 aluminum alloy and strengthening mechanism of vacuum diffusion bonding joint

The diffusion bonding of 6063 aluminum alloy with surface pretreatment was carried out in this paper. The 6063 aluminum alloy (AA6063) is often used in the manufacture of micro-channel heat exchangers (PCHE). However, due to the existence of a stable surface oxide film (Al₂O₃) with a high melting point, which prevents the close contact of the surface to be bonded and the diffusion of atoms. This paper designed the acid and alkali washing cleaning before the bonding process. Three protection schemes were designed for the cleaned surface protection, namely, ethanol protection, α-terpineol surface protection, and magnesium powder terpineol mixed protection. The bonding temperature of diffusion bonding was 540 ~ 580 °C, the pressure was 4 MPa, and the bonding time was 120 min. The microstructure of the joint was studied by scanning electron microscopy. The mechanical properties of the joint were evaluated by a tensile test. The results show that with the optimal process of 570 °C–4 MPa–120 min, the α-terpineol-protected joint achieved a tensile strength of 113.3 MPa and an elongation of 28.1%. It provides a feasible design idea for the diffusion bonding of 6063 aluminum alloy.