Interfacial investigation and mechanical properties of Al-glass-Al anodic bonding process

The Al-glass-Al joint was successfully bonded by the two-step anodic bonding process. The bonding current in each step of the two-step bonding process was investigated. Scanning electron microscopy (SEM) was performed on the interface for the Al-glass surface. The element profile of the transitional layer was investigated by glow discharge optical emission microscopy (GD-OES). Atomic force microscopy analysis (AFM) was done to investigate the surface roughness on Al-glass. Tensile tests were executed to evaluate the bonding strengths of the specimens. The results indicated that all Al-glass joints displayed a homogeneous microstructure without voids or cracks. There were no differences for the interfacial microstructure between the two sides of the Al. It was also found that Al migrated into the Na⁺ depletion region, the quantification of Na⁺ along the depth direction of Al(1)-glass was larger than the Al(2)-glass. Atomic force microscopy mapping results indicated that sodium precipitated from the back of the glass, which makes the roughness of the surface become coarse. The fracture occurred at the glass-Al(2) interfacial area and the Al was destroyed.