Applying liquid film protection method to solid-state bonding process of AA7075 aluminum alloys

Liquid film protection (LFP) method combined with press bonding technique was employed to perform solid-state bonding experiments of AA7075 aluminum alloy in this study. The purpose of this study is to demonstrate the applicability of this new solid-state bonding process to common non-superplastic aluminum alloys. A liquid film protection (LFP) technique is used in this process to protect bonding surface from contacting the environment instead of the expensive vacuum and atmosphere protection equipments prior to press bonding. Effectiveness of this process is studied for various combinations of process parameters, the bonding temperature, the amount of press deformation, and the holding time. Metallographic observations reveal that the bonding interface looks like a wiggled line showing an evidence for a good solid-state bonding. The highest bonding strength and contact ratio reached in this study are 169.3 MPa (about 63% of the base metal) and 82.6%, respectively. Experimental results indicate that press deformation is by far the essential parameter in solid-state bonding process. The bonding strength and the contact ratio tend to increase with deformation. Experimental results also show that fine grains possessed by superplastic materials do increase the bonding strength and contact ratio, but the contribution is very small. The way to provide a clean surface without oxide film is the key factor for a successful solid-state bonding of aluminum alloys.