Diffusion Bonding of Ti 6Al 4V and AZ31 Using Ni Foil

摘要

In this research work, the diffusion bonding process is utilized to fabricate joints using thin (20μm) nickel foil placed between the two bonding surfaces to help facilitate joint formation. Bonding parameters were optimized and their effects on the formation of an eutectic liquid at the joint and on joint microstructure were investigated. The results showed that the bonding time had a direct effect on the joint width produced. Metallographic examination showed that the joint width increased from 86 μm at a bonding time of 5 minutes to 197 μm at 20 minutes. A decrease in joint width to 144 μm at bonding time of 30 minutes showed that isothermal solidification starts for a bonding time of 20 minutes. The micro-hardness measurements of the new phases and intermetallics formed in the joint region showed a variation in the joint hardness. A gradual change in micro-hardness profiles was obtained at 515 °C, 20 minutes and 0. 2 MPa, and results showed a gradual decrease in value from 450 VHN within the Ti-alloy to 90 VHN in the Mg-alloy. A variation in bonding time from 5 to 30 minutes showed a corresponding change in micro-hardness values within the joint region. These results suggested that the hardness is directly influenced by the type of phase formed and the bonding time. This work also investigated the use of ultrasonic testing (UT) as a non-destructive testing(NDT) technique to assess the quality of the joint produced. A direct correlation between the length of bonding time and reflection of sound waves with the bonded area was established.