Microstructural evaluation and mechanical properties of the diffusion bonded Al/Ti alloys joint

• Transient liquid phase (TLP) is a preferred joining process for joining Al to Ti alloys.
• Process parameters significantly affect the microstructure and joint quality.
• Increasing bonding time increases the interface hardness.
• Maximum strength of 30 MPa was achieved in 60 min bond with 50 μm thick interlayer.

Two dissimilar Al7075 and Ti–6Al–4V aerospace alloys were transient liquid phase (TLP) bonded by coating the joining surfaces with Cu and using Sn–4Ag–3.5Bi as interlayer at 500 °C with a holding pressure of 2 MPa. Bonds were made using two different interlayer thicknesses (50 and 100 μm) for various bonding times and the joint interface properties were evaluated. The microstructure of the interface zone was investigated by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The results showed that as the bonding time increases, the concentration of Sn reduces at the joint center and diffusion of atoms leads to the formation of intermetallic compounds. In addition, the bonding process was completed at longer times when the 100 μm thick interlayer was used. Mechanical properties of the joint were examined by measuring microhardness and shear strength. It was seen from the results that the joint interface hardness increases as bonding time increases. Moreover, at higher bonding times, the strength of the bonds decreases due to the growth of brittle intermetallic layers.