Abstract:7075 Al alloy and AZ31B Mg alloy were joined by diffusion welding technique at pressure 29 MPa with various welding temperatures and durations. Scanning electron microscopy examination, shear tests and microhardness evaluation were conducted on the samples interface to find out the effect of welding temperatures and durations on the weldability. The results demonstrate that the AZ31B Mg/7075 Al composite plates are bonded well and the intermetallic phases such as Al₁₂Mg₁₇ and Al₃Mg₂ within the joint zone form. It is found that due to the grain coarsening and the formation of brittle compounds, high welding temperatures and long welding durations result in a decrease of shear strength and increase of interfacial welding hardness. The minimum shear strength of 15 MPa along with the maximum microhardness of HV 176 are obtained for the diffusion couple processed at 450 °C for 120 min.It is revealed that enhancing the temperature and choosing appropriate holding time makes a remarkable increase of interfacial welding thickness. Increasing the welding temperature from 430 to 450 °C along with long welding duration (120 min) results in the increase of interfacial welding thickness by 26% where this value is 6% at the welding performed for 60 min.

Key words: Al alloy; Mg alloy; diffusion welding; welding temperature; welding duration