Study On Influence Of Rolling And Diffusion On Microstructure Of AZ31/AZ91Magnesium Alloy Welded Joint

There is less study on welding performance of deformation magnesium alloy due tolow plasticity, poor weld ability. TIG welding is widely used in the same magnesium alloy,but as a result of different magnesium alloy have huge difference in performance, it isnecessary to study dissimilar magnesium alloy in TIG welding ways. In order tounderstand the variation rule in the microstructure of dissimilar magnesium alloy weldedjoint, the AZ31/AZ91magnesium alloy welded joint was prepared with TIG weldingmethod, and use the small rolling mill rolling AZ31/AZ91magnesium alloys, to getdifferent rolling state alloy deformation, then proceeding annealing treatment. Usingmicroscope rolling reduction and diffusion annealing AZ31/AZ91magnesium alloywelding joint microstructure. Study the rolling reduction and annealing the spread ofAZ31/AZ91magnesium alloy welded joint by scanning Al element composition of AZ31side at fusion zone for AZ31/AZ91magnesium alloy with different rolling reduction useSEM+EDS after different diffusion annealing time and temperature.The results show that the refinement degree of grain within the fusion zone ofAZ31/AZ91magnesium alloy welded joint increases after diffusion annealing treatment at390℃(420℃) for2h, while the grain size gradually becomes larger due to the extension ofdiffusion annealing time and completion of recrystallization after the diffusion annealingtreatment at390℃(420℃) for8h, and microstructure coarsening with the increase ofdiffusion annealing temperature as well as the extension of diffusion annealing holdingtime. During the diffusion annealing treatment at390℃for2h, the diffusion coefficient ofAl atoms within the fusion zone after original,7.5%and15%rolling reductions were0.89×10-12m2/s,1.03×10-12m2/s and1.15×10-12m2/s respectively, that is the diffusioncoefficient will increase with increasing the rolling reduction. During the diffusionannealing treatment at390℃for8h, the diffusion coefficient of Al atoms within the fusionzone after original,7.5%and15%rolling reductions were0.55×10-12m2/s,0.46×10-12m2/s and0.31×10-12m2/s respectively, that is the diffusion coefficient will decrease withincreasing the rolling reduction. During the diffusion annealing treatment at420℃for2h,the diffusion coefficient of Al atoms within the fusion zone after original,7.5%and15%rolling reductions were1.42×10-12m2/s,2.09×10-12m2/s and2.30×10-12m2/s respectively,the diffusion coefficient will increase with the temperature raise. During the diffusionannealing treatment at420℃for8h, the diffusion coefficient of Al atoms within the fusionzone after original,7.5%and15%rolling reductions were0.61×10-12m2/s,0.52×10-12m2/sand0.39×10-12m2/s respectively, the diffusion coefficient will decrease with extending thediffusion annealing time. The diffusion activation energy of original state is great differentfrom the diffusion activation energy of7.5%and15%rolling states after short diffusion. Inlong diffusion, the diffusion activation energy of original state is similar with the diffusionactivation energy of7.5%rolling reductions, and great different from the diffusionactivation energy of15%rolling reductions. The change rule of the diffusion constant issimilar with the diffusion activation energy.