Study On Microstructure And Properties Of AZ31 Alloy By Asymmetric Forge-extrusion Process

Magnesium alloy has great application prospects in the global lightening boom,but due to its six-row dense crystal structure,there are fewer slip systems that can be activated during deformation,and the processing and forming ability of magnesium alloys is poor.The low plasticity of the alloys restricts the development of magnesium alloys.In addition,the weak strength of magnesium alloys is also one of the factors restricting the development of magnesium alloys.Therefore,improving the mechanical properties of magnesium alloys and increasing the strength and plasticity of magnesium alloys are important to the industrial application and promotion of magnesium alloys.The fine-grain strengthening mechanism can improve the strength and plasticity of magnesium alloys at the same time.Conventional processing methods can refine the grains of magnesium alloys,but the refining effect is limited.Although the Severe Plastic Deformation(SPD)technology has a good effect on grain refinement,the SPD technology has high cost and high equipment requirements,which has obvious limitations in the promotion and application of ultra-fine grain deformed magnesium alloy materials.Therefore,the development of plastic processing technology with good grain refinement effect and simple technology is is of great significance to the large-scale application of magnesium alloys.On the basis of conventional extrusion,this article innovatively develops conventional extrusion into a asymmetric forge-extrusion process with forge and continuous extrusion process.That is,the diameter of the billet is smaller than the diameter of the extrusion barrel,and the alloy is pre-deformd in the extrusion barrel,and then the conventional extrusion is continuously performed to achieve continuous cumulative deformation and achieve the maximum grain refinement effect.At the same time,in the asymmetric forging process,the grain is refined and the texture is better weakened under the shear stress.In this paper,optical microscopy(OM)and electron backscatter diffraction(EBSD)and other methods are used to study the asymmetric forge + extrusion process and the asymmetric forge-extrusion process with different deformations.The microstructure and texture of extruded AZ31 magnesium alloy were tested for mechanical properties,and the mechanical properties of extruded products were explored.Using OM and EBSD methods,the asymmetric forge process and extrusion process of asymmetric forge + extrusion process and asymmetric forge-extrusion process were analyzed.The purpose is to study the microstructure evolution and genetic mechanism of AZ31 magnesium alloy in the asymmetric forge-extrusion process,to understand the influence of process parameters on the mechanical properties of the alloy,and to optimize the asymmetric forge-extrusion process parameters to provide a theoretical basis for the industrialization of the process.The main results obtained are as follows:(1)For the asymmetric forge + extrusion process,with the increase of the deformation of the pier,the degree of recrystallization of the AZ31 magnesium alloy is improved,the strength and plasticity are improved,the anisotropy is improved.Among them the ingot extruded product whose forge effect is 0.25 has the best effect,the tensile strength reaches 269 MPa,and the elongation reaches 18.7%.(2)For the the asymmetric forge-extrusion process,compared with the asymmetric forge + extrusion process,it makes better use of the effect of forge to continuously extrude.By improving the nucleation rate during the extrusion process,the structure after extrusion is more fine and uniform,the texture is weaken,plasticity and strength of extrusion bar are greatly improved.Among them,Among them the ingot extruded product whose forge effect is 0.39 has the most obvious improvement,with average grain size reaching 3.60μm,tensile strength reaching 312 MPa,and elongation reaching25.4%.(3)In the asymmetric forging extrusion process,the larger the extrusion ratio,the more twins are produced in the initial stage of the extrusion process,and the time of occurrence is earlier.The subsequent dynamic recrystallization degree is also higher,and the plasticity of AZ31 magnesium alloy is improved.Obviously,the anisotropy has been significantly reduced.