Papers by Keyword: AZ31 Alloy

Abstract: The paper researched formability ability of AZ31 Mg-alloy tube by hot pneumatic bulging. FEM simulations were carried out to reveal the effect of internal pressure changing on bulging process and forming limit. Several loading paths with different pressure changing were used in the simulations. From the research, the original expansion ratio of diameter using a bilinear loading path, namely the internal pressure was increased linearly, is only 22%, and bursting occurs quickly. With a step-like loading path, namely the internal pressure is increased step by step, among the steps, the pressure is kept constant, and the strain rate of bulging can be kept into a small range. Thus the deformation around the hoop direction is more even than the linear loading path, and than bursting can be postponed. During bulging, the inner pressure should be lowered with the increase of diameter to keep the strain rate in a small range around a constant value. Through optimization of loading path, the forming limit can be enhanced obviously so that the expansion ratio of diameter can be increased to 25.1%.

Abstract: The yield and plastic deformation behaviour of wrought Mg-alloy AZ31 sheets were investigated at elevated temperatures from ambient to 300°C. It is found that the 0.2% proof stress and ultimate strength decrease linearly with increasing temperature, and the Young’s modulus goes down in the same way. Whereas the ductility, expressed by elongation, increases with temperature, in contrast to the decrease in uniform elongation. The plastic deformation anisotropy, represented by the ratio of transverse and thickness strain of the plate sample, decreases as the temperature increases, and at about 225°C, coincidentally, reaches to unity. The activation volumes for yield stress and ultimate strength are discussed with a thermal activation law-Arrhenius Equation.

Abstract: The hot-rolled and extruded AZ31 specimens are subjected to tensile tests at room and elevated temperatures. At room temperature, the yield stress of the hot-rolled specimen is significantly higher than that of the extruded, the reason for which is related to the different textures developed in the two type specimens, as well as the different slip systems activated. At elevated temperatures, the strain rate sensitivity and the activation energy are obtained to characterize the deformation mechanism of the alloy during the temperature range of 423~573K.

Abstract: Mechanical properties and high temperature deformation behavior of AZ31-0.84%Sb alloy have been studied. The results show that small additions of antimony to AZ31 alloy effectively enhanced the creep resistance and the ultimate tensile stress of the alloy at elevated temperature. One of the reasons for the improved high temperature properties is the high volume fraction (~20%) of the precipitates, as Mg3Sb2, which effectively hindered the movement of dislocations during the elevated temperature deformation. Considerable amounts of twins were formed during creep failure of AZ31-0.84%Sb alloy. Within the twins, many dislocation pile-ups were present on both basal and non-basal plane of magnesium matrix.

Abstract: Microstructure evolution and mechanical properties of AZ31 Mg alloy during equal channel angular extrusion (ECAE) at the temperature range of 453-498K was investigated. The processing temperature is an important factor to affect the microstructure and mechanical properties of the Mg alloy during ECAE. ECAE processing can be practiced at 498k or upon the temperature for as-received AZ31 alloy. A new two-step ECAEed processing was successfully used with lowing the processing temperature to 453k. The ductility increased but yield stress decreased though the grain refinement after ECAE at 498k because the recrystallization took place and large angle grain boundary formed. However both the ductility and yield stress were increased after two-step ECAE, which was ascribed to grain refinement as well as incomplete dynamic recovery and recrystallization during the processing.

Abstract: Grain refinement in a magnesium alloy AZ31 was studied in multi-directional forging (MDF) at a strain rate of 3×10-3s-1 with decreasing temperature from 623K to 423K. The MDF was carried out up to large cumulative strains with changing the loading direction during decreasing temperature from pass to pass. The structural changes were characterized by generation of many mutually crossing kink bands at low strains, followed by development of very fine grains at large strains. The results showed that MDF with decreasing temperature can accelerate uniform generation of much finer grains, resulting in the minimal grain size of 0.36µm in a cumulative strain of 4.8 at 423K. The mechanism of grain refinement was discussed.

Abstract: 4-pass ECAE processing was applied to two kinds of magnesium alloys, AZ31 and ZK31. Subsequently, hot rolling was carried out as a secondary forming process. After ECAE processing, the samples have fine and equiaxed grains. The basal plane of AZ31 alloy is inclined at about 450 to the extrusion direction, while that of ZK31 alloy is parallel to the extrusion direction. As a result, tensile strength and 0.2% proof stress of ZK31 alloy are higher than those of AZ31 alloy. On the other hand, the basal plane orients parallel to the rolled surface in the Subsequently rolled samples and, therefore, tensile strength and 0.2% proof stress are improved significantly. Furthermore, the AZ31 alloy has higher ductility than ZK31 alloy.

Abstract: An AZ81 magnesium alloy, which was processed by hot extrusion in advance, was tested in the temperature range of 473 ~ 623 K and at various initial strain rates, ranging from 1×10-1 to 1×10-4 s-1. True stress-true strain curves under various temperatures and activation energy within different temperature range were investigated for the analysis of effect of temperature on superplastic behaviors. Elongation of the as-extruded AZ81 alloy increased with temperature when tested at the same initial strain rate. Elongation values, obtained at the same initial strain rate of 1×10-3 s-1, were 94% at 473K and 446% at 623K, respectively. Deformation mechanisms varied with increasing temperature, from the grain boundary sliding (GBS) accommodated by grain boundary diffusion to the GBS accommodated by lattice diffusion, transition temperature was 573 K.

Abstract: The square-cylindrical cup of AZ31 Mg alloy with a depth of 50mm and a width of 50 mm was successfully deep drawn from a rolled sheet with a thickness of 0.5 mm using a hydraulic press machine with a capacity of 60 tons. The blank was heated between the die and the blank holder kept in a temperature of 300 oC .The forming time was about 3 seconds. The fine-grained microstructure was observed at the corner with a sever strain. The grain refinement caused by the dynamic recrystallization contributed to generate high strain-rate superplasticity.