Migrating behaviors of interfacial elements and oxide layers during diffusion bonding of 6063Al alloys using Zn interlayer in air

The oxide layer on the surface has always been a key obstacle to achieving the diffusion bonding of Al alloys. It is a challenge for performing diffusion bonding without removing oxide layers. Herein, diffusion bonding of Al alloy retaining continuous oxide layers was successfully achieved in the air by a low-temperature and low-pressure diffusion bonding mothed using a Zn interlayer. During the bonding processes, conducted at 360 °C and 3 MPa, Zn diffused into Al through cracks of thin oxide layers to form the joint composed Al/(diffusion layer)/(oxide layer)/(Zn)/(oxide layer)/(diffusion layer)/Al. The diffusion layers were composed of Zn-Al eutectoid, and the oxide layer included nanocrystals and amorphous Al2O3. The shear strength of joints containing continuous oxide layers was about 30 MPa. Interestingly, the migration behavior toward the joint center of the interfacial oxide layers was observed with consuming of the Zn interlayer. The cracking phenomenon, the “subcutaneous diffusion” and the migration behavior of oxide layers were verified and analyzed by the diffusion bonding of anodized 6063Al-6063Al. Subsequently, the dynamic migration mechanism of oxide layers with elements diffusion and bonding interface strengths were discussed in detail. The ability to join Al alloys in the air at low temperatures and low pressure suggests a highly practical and economic method for diffusion bonding.