Research On The Microstructures And Mechanical Properties Of AZ91D Magnesium Alloy Extruded At Various Conditions

Through the extruding experiment of AZ91D Mg alloy in different forming conditions and the experiment of the non-circular hole joint forming, the plastic deformation behaviors of AZ91D Mg alloy at different temperatures are studied in this thesis. And supply a reliable basis for the development and application for the deformation technology of AZ91D Mg alloy.DRX(Dynamic Recrystallization) occurs during the extrusion of AZ91D alloy, resulting in a marked refinement of grain size. At a given extrusion ratio, with the increase of extrusion temperature, DRX fraction increases and the average size of recrystallized grains increases. At a given extrusion temperature, with the increase of extrusion ratio, DRX fraction increases and the distribution of recrystallized grains tends to uniform. When DRX is completed, the average size of recrystallized grains decreases with the increase of extrusion ratio.By increasing the extrusion ration, the tensile strength decreases and the elongation increases, compared with the AZ91D alloy in casting.The microstructure was more homogeneous when the temperature contrast between die and specimens was 100℃. The microstructure was homogeneous equiaxed grain which was 8μm when the die and the specimen were 400℃and 300℃with the extruding ratio was 9:1.The dissertation made the numerical simulation for the forming processing of the non-circular hole joint part. Some different influence factors for the warm backward extrusion were analyzed, including different friction conditions, processing temperatures and extrusion speeds. Through the analysis of the processing technology for non-circular hole joint part, the dissertation present the equivalent stress distributing, equivalent plastic strain distributing etc. And the feasibility of the forming of non-circular hole joint part in AZ91D alloy was proved by experiment results and numerical simulation results.