EFFECT OF BONDING PRESSURE ON JOINT FORMATION BY DIFFUSION BONDING OF Ti-6Al-4V AND Mg-AZ31

摘要

Magnesium is the lightest structural metal and recently magnesium and its alloys have received increased attention in various engineering applications. Titanium is a light metal and shows excellent corrosion resistance and high specific strength. The ability to join these two metals together can increase their use in the automotive and aerospace industries. However, differences in the physical properties of these alloys (e.g. melting point for Ti-6Al-4V is 1650°C and 680°C for AZ31) make the joining of these dissimilar alloys a great challenge. This research work presents the effect of one of the most important parameters in diffusion bonding; the bonding pressure. Optimizing bonding parameters resulted in sound joint with homogeneous microstructure and suitable mechanical properties. To join these two alloys the diffusion bonding was carried out using thin (20μm) pure Ni foils at different bonding pressures (0.2 and 0.7 MPa) at 515°C as a function of holding time of 5 to 30 minutes. The results showed a direct relation exist between bonding pressure, joint microstructure and mechanical properties. Reaction zones were identified inside bonding region and tested with respect to hardness profile. In case of 0.2 MPa pressure the joint width increased from 86um for bonding time of 5 minutes to 197μm for 20 minutes. A decrease in joint width to 144μm at bonding time of 30 minutes shows that isothermal solidification starts for a bonding time of 20 minutes. However, when bonding at 0.7 MPa pressure the joint width increased from 59 μm for bonding time of 5 minutes to 156 μm at 10 minutes. A decrease to 123 μm at bonding time of 20 minutes was recorded. Even further decrease to 75 μm at bonding time of 30 minutes was noticed. This suggest Isothermal solidification takes place in case of 0.7 MPa earlier than in case of 0.2 MPa.