On The Grains And The Mechanical Properties Of AZ31Magnesium Alloys Fabricated By Warm Constrained Groove Pressing

Depending on low density and electromagnetic shielding performance,the magnesium alloys were widely used in the fields such as the automobile,communication and the electronic equipments. However, low ultimate tensilestrength of magnesium alloys limits its further application. According tometallography principle, when the grains of metal materials are refined tosome a size, its ultimate tensile strength will be improved significantly.Therefore, the preparation of the fine-grained magnesium alloys is worthstudying. In the present study, the warm constrained groove pressing (CGP)was used to refine the grains of AZ31magnesium alloys, analyzing theinfluence of the recrystallization annealing treatment, warm constrainedgroove pressing and stress-relief annealing for AZ31magnesium alloys,improving its mechanical properties and extending its application areas.The recrystallization annealing treatment of AZ31magnesium alloysbefore CGP was determined by analyzing the microstructure and mechanicalproperties. It was found that the sample was annealed at275℃for60minutes, the grains were small and the microstructure showed homogeneous, theaverage grain size of the sample was decreased from29.8μm to19.8μm, theelongation was increased from9.6%to17.72%. The treatment of275℃×60min was used as the annealing treatment of AZ31magnesium alloys beforeCGP.The DEFORM-3D software was used to simulate the process of CGP,investigating the value of the effective strain and its distribution in the sheetafter the corrugation of the CGP process in this paper. The theoretical value ofthe effective strain was calculated according to the theory of the metal plasticdeformation. The results showed that the theoretical value of the effectivestrain during CGP was0.58. The simulative results showed that distribution ofthe effective strain in the sheet was homogeneous and the effective-strainvalue obtained by DEFORM-3D was equal to the theoretical value.The grains refinement and the mechanical properties of AZ31magnesiumalloys fabricated by warm CGP, and the grains and the mechanical propertiesof the warm CGPed sample annealed at260℃for15min were discussed inthe paper. After a complete warm CGP process at200℃，the average grainsize was refined from19.8m to9.2m, and the degree of grain refinementwas up to53.54%. The ultimate tensile strength and the yield stress increasedwith grain refinement, from240MPa and132MPa to285MPa and155MPa,respectively. The hardness of sample was improved from55.84HBW to69.16HBW while the elongation was decreased from17.72%to12.29%. When the one warm CGPed sample was annealed at260℃for15min, the average grainsize was increased from9.2m to10.3m. The ultimate tensile strength andthe yield stress were decreased from285MPa and155MPa to280MPa and143MPa, respectively. The elongation of the sample was16.2%and thehardness was58.48HBW.