Study On Deformation Microstructure And Properties Of AZ12 Magnesium Alloys

AZ12 magnesium alloy has the characteristics of low density and high specific strength due to low alloying degree.However,the hexagonal crystal structure and the non-aging treatment characteristics result in poor plastic deformation ability and low mechanical strength.In order to improve the mechanical properties of AZ12 alloy,the plastic deformation microstructure and properties of the alloy were studied in this paper.Firstly,the initial microstructure and properties of AZ12 magnesium alloy slab prepared by LFEC method were characterized.The density of the alloy is 1.77×10~3kg/m~3 which is equivalent to AZ31.The slab structure consists of the edge columnar cystal,the central equiaxed crystal and the core coarse cystal.The macrosegregation is mainly concentrated in the central part of the ingot.The mechanical strength of the core and the edge of the ingot is higher,and the mechanical strength of the middle region is lower and the elongation is higer.Secondly,the as-cast AZ12 alloy was used as experimental material for thermal compression experiments to study its hot deformation behavior.The results show that the deformation temperature and deformation rate have a significant effect on the deformation process of AZ12 alloy.The rheological curve of the alloy is unimodal and the deformation process is divided into work hardening,recrystallization softening and steady state by working hardening and dynamic recrystallization softening.The accuracy of the Arrhenius-type constitutive equation based on the thermal deformation data is higer than that of the Johnson-Cook constitutive equation,and the constitutive equation was used to simulate the influence of temperature on the deformation behavior of the rolling plate during rolling.The results show that temperature is an important factor in the plastic deformation process of AZ12 alloy and provides a theoretical basis for the inflence of temperature on microstructure in extrusion process.Finally,the effects of extrusion temperature on the microstructure and mechanical properties of AZ12 alloy were studied by using AZ12 alloy at different temperature conditions.The results show that as the extrusion temperature decreases,the mechanical properties increase gradually and the grain size decreases.The decrease of grain size leads to the enhancement of fine grain strengthening and the mechanical properties of the alloy.AZ12 magnesium alloy can achieve low temperature extrusion.When extruded at 110?,the grain size is refined to 680nm and the tensile strength can reach 332MPa while the elongation is 23%.The new ultra-low temperature extrusion technology developed for AZ12 magnesium alloy can obtain sub-micron ultra-fine crystal,which can significantly improve the mechanical properties of magnesium alloy while ensuring excellent plasticity.The extrusion limit temperature of AZ12 alloy is explored and basic data and theory were provided to improve the mechanical properties of the alloy.