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The strain path dependence of the compressive flow behavior of cast AZ31 magnesium alloy was investigated. Biaxial compression tests with linear strain paths were conducted using a unique biaxial compression device. It was found that the equivalent stress-strain relations varied according to the strain paths. The work contour for linear strain paths was well described by the Logan-Hosford yield criterion. Biaxial compressions with abrupt strain path change were also carried out to investigate the influences of the prestrain amplitude and angular relation of the sequential strain paths on the flow behavior. Rapid increase in the equivalent stress was observed just after the abrupt strain path change. These specific flow behaviors were discussed with regard to the plastic anisotropy, which showed rapid evolution in the early stage of the biaxial compressions.

The objective of this study was to experimentally determine the properties of magnesium alloys during plastic deformation under various temperature regimes. Proportional loading tests combining both axial and torsional loads were performed on cylindrical AZ31 Mg alloys in a range from room temperature to 673 K, where superplasticity has a high probability of occurrence, and the crystalline structures of the samples were observed after these tests. The above observations indicate that the deformation mechanisms in AZ31 Mg alloy are dominated by twinning deformation at 300 K and 423 K, and by grain boundary sliding promoted by dynamic recrystallization at 523 K and higher temperatures.

This paper describes the effect of hot extrusion on the microstructure and mechanical properties of electromagnetic continuous cast (EMC) AZ31 alloy. The microstructure, mechanical properties and fracture surfaces of AZ31 alloy before and after extrusion were investigated. The results demonstrate that extrusion processing gives rise to a strong basal texture. The grains are significantly refined and the average grain size of localized fine grain area is 2μm. Compared with EMC ingots, as-extruded specimens have much finer grain size and more uniform microstructure, and the second phase (Mg₁₇Al₁₂) becomes smaller and distributes more uniformly. The mechanical properties of the deformed AZ31 were improved after hot-extrusion. When the extrusion ratio was 10, the yield strength, ultimate tensile strength and reduction in cross-sectional area of as-extruded AZ31 alloy were 248MPa, 306MPa and 28.44%, which were respectively enhanced by 78.4%, 41% and 45.25%, compared with those of as-cast samples. With the increase of extrusion ratio, the grain refining effect was more significant and the microstructure was more uniform. The yield strength, ultimate tensile strength and reduction in cross-sectional area increased obviously with increasing the extrusion ratio. The observation on fracture surfaces demonstrates that the fracture mode changes from ductile-brittle fracture to ductile fracture after extrusion.

This work aims to discover the effects of ultrasonic vibration and heat pipe assistance during the friction stir welding (FSW) of AZ31 magnesium alloy. The microstructure and mechanical properties of FSWed AZ31 alloy were investigated. The ultrasonic vibration and heat pipe assistance can promote the dynamic recrystallization of AZ31 magnesium alloy during the FSW process, which reduces the inhomogeneous microstructure and the grains and weakens the texture intensity of the FSWed AZ31 alloy. The microstructure and texture of the joint are regulated by the ultrasonic vibration and heat pipe assistance, to enhance the tensile strength, elongation and microhardness.

The grain size of as-extruded AZ31 magnesium alloy was refined by isothermal annealing pretreatment through orthogonal experiment. By using the Gleeble-3800 thermal simulator, the compression superplasticity of as-extruded AZ31 magnesium alloy was studied. The high strain rate superplastic compression was realized. The process parameters of the superplastic compression were established and the mechanism of the superplastic deformation was analyzed. The effects of deformation temperature and strain rate on the superplastic flow were investigated. The results indicated that at 250°C–300°C and strain rate at 1×10^-2s^-1, the true strain values were all more than 2.03. As the temperature was 300°C and the strain rate was 1×10^-2s^-1–1×10 s^-1, the true strain values were all more than 2.18. The results showed that the as-extruded AZ31 magnesium alloy being refined presented good compression superplasticity. The main mechanism for the superplastic compressive deformation of the as-extruded AZ31 magnesium alloy was grain-boundary sliding, meanwhile, dynamic recrystallization also played a harmonious role during the superplastic deformation.

After micro-arc oxidation, the surface properties of AZ31 magnesium alloy have been improved. However, micro-arc oxidation treatment leads to high insulation, which limits its application in electronic devices. To increase conductivity, a conductive coating was developed by adding multi-walled carbon nanotubes (MWCNTs) to the epoxy resin. The microstructure and performance of the coating were tested by SEM, thermogravimetric analyzer, four-probe conductivity meter, high-temperature friction and wear tester, and electrochemical workstation. The results indicate that the optimal conductivity with a resistivity of 303$\mathrm{\Omega }\cdot$m is obtained when the MWCNT content is at 4wt%. In addition, MWCNTs are filled with a network structure of epoxy resin, which increases the density of the coating and enhances their wear and corrosion resistance.

In the present work, the microstructures, textures and tensile mechanical anisotropy of AZ31 magnesium alloy sheets processed by different final rolling routes (Route A, B and C) at 550° were investigated, in which the final rolling direction is parallel, perpendicular and at angle of 45° to initial rolling direction (RD) of the sheet, respectively. The results showed that the AZ31 alloy sheets processed by route A, B and C exhibited double-type textures with basal poles tilting at approximately from 9.5° to 12° in the RD, TD and 45° to RD, respectively. By changing the final rolling route from Route A to C, the grain sizes of the sheets were not refined and the basal texture intensity was slightly increased, but the planar anisotropy in strength gradually decreased. The main reason was that the difference of the Schmid factors for basal plane slips among tensile tests conducted along RD, 45° and TD was decreased, which was determined by texture characteristics, including the final tilted directions and angles of basal pole, and the texture intensity.

In order to solve the complex problems of manufacturing process of automobile hydraulic shock absorber shell, the technology of hot extrusion was presented. Based on the rigidplastic finite element analysis method, numerical simulation of extrusion process of AZ31 agnesium alloy cylindrical shell was carried out by by using the Deform-3D finite element simulation software. The stroke - load curve in extrusion process and the distribution of velocity field of flow metal were analyzed. The influence of different process parameters on the extrusion force and specimen quality were analyzed also. The results show that there are four stages in the process of extrusion deformation, including heading-deformation stage, lug blank forming stage, composite extrusion stage and the final forming stage. When the initial temperature of the blank is set to 350°C, the die preheating temperature is set to 280°C, and the working speed of the male die is controlled in the range of 6 ˜ 12 mm/s, the load platform is stable, the forming quality of the cylinder shell is higher. And the feasibility of the technology is verified by experimental method. The study provides a theoretical basis for the optimization of die design and making reasonable hot extrusion process parameters.

Based on the rigid-plastic finite element method, the extrusion process of AZ31 magnesium alloy cylindrical shell was simulated numerically in this paper. Concurrently, the distributions of equivalent strain field, equivalent force field and temperature field in the extrusion process were analyzed. In addition, the influence of the blank temperature and preheating temperature of the die on extrusion pressure and the quality of the test pieces were analyzed. The results demonstrate that the deformation of the blank bottom and lug part is the most severe in the whole extrusion process and it exhibits a higher temperature than the other parts. The contact area between the edge of male die head and the blank; the area of deformation in the cylinder wall; the contact area between the bottom of the blank and the female die; and the area of deformation of the lug are all areas prone to cracks, due to the larger stress caused by the changing speed of flowing metal and compounded by poor lubrication. Under experimental conditions, the optimal deformation parameters of AZ31 magnesium alloy are as follows: the preheating temperature of the blank should be controlled at 350°C and the preheating temperature of die should be controlled between 260°C to 320°C. The precision of the of hot extrusion process for AZ31 magnesium alloy cylindrical shell is verified by numerical analysis and therefore this paper provides a theoretical basis for the optimization of die design and production guidance.

The strain path dependence of the compressive flow behavior of cast AZ31 magnesium alloy was investigated. Biaxial compression tests with linear strain paths were conducted using a unique biaxial compression device. It was found that the equivalent stress-strain relations varied according to the strain paths. The work contour for linear strain paths was well described by the Logan-Hosford yield criterion. Biaxial compressions with abrupt strain path change were also carried out to investigate the influences of the prestrain amplitude and angular relation of the sequential strain paths on the flow behavior. Rapid increase in the equivalent stress was observed just after the abrupt strain path change. These specific flow behaviors were discussed with regard to the plastic anisotropy, which showed rapid evolution in the early stage of the biaxial compressions.

The objective of this study was to experimentally determine the properties of magnesium alloys during plastic deformation under various temperature regimes. Proportional loading tests combining both axial and torsional loads were performed on cylindrical AZ31 Mg alloys in a range from room temperature to 673 K, where superplasticity has a high probability of occurrence, and the crystalline structures of the samples were observed after these tests. The above observations indicate that the deformation mechanisms in AZ31 Mg alloy are dominated by twinning deformation at 300 K and 423 K, and by grain boundary sliding promoted by dynamic recrystallization at 523 K and higher temperatures.