Papers by Keyword: AZ31 Mg Alloy

Abstract: The effect of second phase particles in different shapes on grain growth of AZ31 Mg alloy has been simulated by the phase field methods under realistic spatial-temporal scales. The long-range orientation field variables are chosen to express the temporal microstructure evolution and crystal orientation. The expression of the local free energy density equation was modified by adding the expression term of second phase particles, and the simulated results show that the grain boundary migration is pinned by the second phase particles during the grain growth, which is agree with the Zener pinning observation. When the shape of particles is different and the volume fraction is 10%, the effect of refining grain is different too, the oval particles are the strongest, followed by the rod particles, and the effect of spherical particles are weaker. The research will help to understand the mechanisms of grain growth containing the second phase particles strengthening.

Abstract: This study investigated strain-rate sensitivity (SRS) in an as-extruded AZ31 magnesium (Mg) alloy with grain size of about 10 mm. Although the alloy shows negligible SRS at strain rates of >10^-5 s^-1 at room temperature, the exponent increased by one order from 0.008 to 0.06 with decrease of the strain rate down to 10^-8 s^-1. The activation volume (V) was evaluated as approximately 100b³ at high strain rates and as about 15b³ at low strain rates (where b is the Burgers vector). In addition, deformation twin was observed only at high strain rates. Because the twin nucleates at the grain boundary, stress concentration is necessary to be accommodated by dislocation absorption into the grain boundary at low strain rates. Extrinsic grain boundary dislocations move and engender grain boundary sliding (GBS) with low thermal assistance. Therefore, GBS enhances and engenders SRS in AZ31 Mg alloy at room temperature.

Abstract: TiO₂ films were prepared on the AZ31 Mg alloy substrate by sol-gel method. The morphology was characterized via X-ray diffractometer (XRD), scanning electron microscopy (SEM) and energy disperses spectroscopy (EDS). The corrosion rate of the coated AZ31 mg alloy was tested with the method of orthogonal experiment design. The influence of the hydrolysis temperature, coating times, calcinations temperature and time was investigated.

Abstract: Based on the advantages of Mg alloys, AZ31 alloy profiles were designed for mobile phones cell, and cars, which expanded Mg alloy application and achieved the purpose of environmental protection and energy saving. Tensile strength of the profile reached to 256 MPa, and elongation was 17.9%. The effects of different heat treatment parameters on microstructure and plastic property of AZ31 alloys profiles were studied. After aging heat treatment (T5), the comprehensive mechanical properties at room temperature of the profiles increased. The tensile strength reached to the maximum of 261 MPa, and the elongation reached to 14.3%, after ageing at 225 for 20h. The elongation reached the maximum value of 18.3%, however, the tensile strength decrease to 241 MPa, after aging at 175 for 15h. Moreover, the influence of cryogenic treatment on microstructure and plastic property of the AZ31alloy profiles were studied. The results showed that elongation increased with the increase of treatment time, which would reach to 18.5% after cryogenic treatment. In addition, by cryogenic treatment and aging treatment, the tensile strength improved to 271 MPa. The cryogenic treatment improved obviously the plastic ability of AZ Mg alloys, while normal heat treatment improved it unobviously.

Abstract: Equal-channel angular pressing (ECAP) is used to convert coarse grain into ultrafine grain (UFG). The characteristics of ECAP and the shearing patterns obtained when ECAP applied to metals are investigated. Then propose a series of procedures to verify the structure evolution of AZ31 Mg alloys after ECAP processing. The results indicate that parameters including route, die angular and pressing passes influence on the microstructure of the AZ31 Mg alloys. Route BC is the optimum processing route due to the largest slipping angular range.

Abstract: Abnormal grain growth was simulated by phase field model in order to find ways of producing scattered a few enormous grains in a nano-structural single phase AZ31 alloy to improve its ductility. It is shown that the abnormal grain growth is controlled by the three keys factors of interface energy, strain restored energy and interface mobility. Therefore, the microstructure with scattered a few enormous grains in the nano-structural matrix can be achieved after an annealing treatment if there is a small group of specially orientated nano-size grains in the original nao-structure with local low grain boundary energy or local high strain energy or local high interface mobility. The morphology of abnormal grains is also examined as function of annealing time to optimize the microstructure.

Abstract: For non-SF6 process and melt cleanliness, CaO added AZ31 Mg alloy has been developed for strip casting. Mg alloys were usually ignited during conventional casting, the continuous casting and strip casting. Protective gases should be used in order to prevent the ignition of Mg alloys during melting and casting processes. However, protective gases have the disadvantages of global warming potential, high production cost and corrosion of steel based equipments. To solve ignition problem and overcome environmental issue, this paper discussed the effects of CaO addition and amount on strip casting process in terms of non-SF6 process and melt cleanliness.

Abstract: This study was carried out to characterize thixoextruded AZ31 Mg alloy in terms of its symmetric behavior through the optical microscope, electron back scattering diffraction and mechanical test. The elongated grains to the extrusion direction were generally observed during hot extrusion, while the thixoextruded microstructures were isotropic. Texture of hot extruded bar showed the strong fiber component, while that of thixoextruded bar was random distribution. The aspect ratio of hot extruded bar was irregular at each position. On the contrary, the aspect ratio of thixoextruded bar was almost uniform below 2 at each position.

Abstract: Bending and impact tests were conducted on magnesium alloys AZ31 and AZ80 in different microstructure conditions. It is found that the strength parameters are increased quite a lot, and the ductility parameters (bending flection) decreased with increase in strain rate. The damaged surface analysis in SEM revealed that, the micro crack nucleation modes, micro crack coalescence and final crack path are varied with the stress state on the specimen, and the crack nucleation modes are varied with the initial strain rate. The effect of strain rate on fracture modes is discussed.

Abstract: Hot rolled Mg alloy has a preferred orientation, which affects the deformation behavior of Mg alloy. In this work, load relaxation and tensile tests after hot rolling process were performed to clarify the effect of the texture on deformation behavior of AZ31 Mg alloy and the results were analyzed based on an internal variable theory proposed by one of the authors. The analysis of the deformation behavior is then correlated to XRD pole figure results of the texture. The analysis result of Mg alloy was found to be comparable to the results obtained from the test of Ti alloys, which has the same HCP structure.