Extruded AZ31 Magnesium Alloy Research Articles

Effects of Texture on Tensile Property of Extruded AZ31 Magnesium Alloy Investigated by Acoustic Emission

In this paper, effects of texture on tensile property of extruded AZ31 magnesium alloy are investigated by acoustic emission (AE). The results show that the extruded AZ31 magnesium alloy used in this research has the strong texture of and tensile anisotropy. The yield strength of TD-sample is about 80MPa, which is half of that of ED-sample. AE results show that the AE count of the TD-sample is higher than that of the ED-sample. These AE results suggest that there are more deformation twins in the TD-sample than in the ED-sample. It can be concluded that the deformation twinning can strongly influence the anisotropy, which is mainly due to the flow stress relief induced by twinning and the interaction of twins and dislocations during the strain hardening.

Polycrystalline behavior analysis of extruded magnesium alloy AZ31

Uniaxial tensile and compressive tests were performed at room temperature on extruded AZ31 Mg alloy specimens and distinct tensile-compressive anisotropy was detected. Deformed specimens were examined and the results indicate that the generation of {10\(\bar 1\)2}〈10\(\bar 1\)1〉 twin is responsible for the mechanical anisotropy. A rate independent crystal plasticity model, which accounts for both slip and twinning, was developed for polycrystalline hexagonal close packed (HCP) materials. Model predictions for the stress-strain curves and texture evolution were in reasonable agreement with the experimental results. Specifically, the model captured the three stages of strain hardening for uniaxial-compression. By comparing stress-strain curves and texture evolution between model predictions and experimental measures, information about the dominant slip and twinning systems active at room temperature was deduced.

Effects of prior compression on ductility and yielding behaviour in extruded magnesium alloy AZ31

Effects of prior compression on ductility and yielding behaviour in extruded magnesium alloy AZ31

OS0405 各種温度条件下におけるAZ31マグネシウム合金押出し丸棒材の変形機構

The deformation mechanism of the extruded AZ31 magnesium alloy rod under various temperature conditions was studied. The purpose of this study is to find the yield mechanism of this material in the thermoplastic deformation conditions. When this material is subjected to tensile stress parallel to the extruded direction to which a transgranular deformation and grain boundary sliding are hard to occur by the crystallographic texture, the non basal slip whose critical resolved shear stress decreases with increasing temperature can act as the yield mechanism. After the yield was induced by the non basal slip, two different deformation mechanisms occur according to the environmental temperatures. The c-axis compression twinning which has the temperature dependency occurs at a relatively low temperature. On the other hand, the grain boundary sliding which was promoted by the dynamic recrystallization acts as the plastic deformation mechanism at the higher temperature.

AZ31マグネシウム合金押出し材の常温における降伏曲面に関する実験的研究

The yield surface and the deformation mechanism of the extruded AZ31 magnesium alloy rod at room temperature were studied. The uniaxial tensile, compressive and pure shear tests with the simultaneous observation of the microstructure were carried out for specimens sampled along different directions in an extruded rod. In the plane-stress condition within the plane perpendicular to extrusion, the yield surface almost fits the Tresca's criterion for isotropic materials, because of the activation of the basal slip or {10-12} twinning, regardless of the loading direction. The deformation mechanism with higher critical resolved shear stress than those of basal slip or {10-12} twinning is driven by the tensile loading parallel to extrusion, due to the texture with the direction of its c-axis perpendicular to tensile direction. Therefore the tensile yield stress for this direction increase more than compression or shear, and the twinning pattern at the yield for tensile loading does not appear.

OS0403 AZ31マグネシウム合金押出し材の常温における降伏曲面に関する実験的研究

The yield surface and the deformation mechanism of the extruded AZ31 magnesium alloy rod at room temperature were studied. The uniaxial tensile, compressive and pure shear tests with the simultaneous observation of the microstructure were carried out for specimens sampled along different directions in an extruded rod. In the plane-stress condition within the plane perpendicular to extrusion, the yield surface almost fits the Tresca's criterion for isotropic materials, because of the activation of the basal slip or {1012} twinning, regardless of the loading direction. The deformation mechanism with higher critical resolved shear stress than those of basal slip or {1012} twinning is driven by the tensile loading parallel to extrusion, due to the texture with the direction of its c-axis perpendicular to tensile direction. Therefore the tensile yield stress for this direction increase more than compression or shear, and the twinning pattern at the yield for tensile loading does not appear.

Characterizing the Cyclic Behaviour of Extruded AZ31 Magnesium Alloy

In this paper, the mechanical behaviour of extruded AZ31 magnesium alloys under multiaxial fatigue loading conditions is studied. The monotonic properties of the AZ31 magnesium alloy were determined by tests on the specimens which were machined from extruded rods. Then, the cyclic deformation under multiaxial loading conditions was simulated by ANSYS and a plasticity program with the Jiang & Sehitoglu plasticity model. The fatigue lives were estimated by the critical plane models coupled with Coffin-Manson rule, such as Findley, Fatemi-Socie, Brown-Miller, SWT and Liu models. Four loading paths were considered with different levels of non-proportionality, the results show significant loading path dependence.

The Effect of Reversed Loading Conditions on the Mechanical Behaviour of Extruded Magnesium Alloy AZ31

The Effect of Reversed Loading Conditions on the Mechanical Behaviour of Extruded Magnesium Alloy AZ31

Deformation mechanism and softening effect of extruded AZ31 magnesium alloy sheet at moderate temperatures

The flow stress behavior of extruded AZ31 magnesium alloy sheet was investigated by means of compression tests at temperatures between 473 and 523 K and strain rates ranging from 0.001 to 1.0 s−1. The deformation activation energy of the sheet in extrusion direction (ED) was calculated, and the relationship between the softening effect and deformation mechanism was elucidated by optical microscopy and transmission electron microscopy. The results show that when the extruded AZ31 magnesium alloy samples were compressed at moderate temperatures in ED direction, the deformation activation energy is 174.18 kJ/mol, which means that dynamic recrystallization (DRX) is the main softening effect and is controlled by cross slip of thermal active dislocation. Dislocation slip is the main deformation mechanism in moderate-temperature deformation process except twinning. The main DRX effect at moderate temperatures can be considered to be continuous dynamic recrystallization accommodated with twinning DRX.

Study of lattice strains in magnesium alloy AZ31 based on a large strain elastic-viscoplastic self-consistent polycrystal model

The recently developed large strain elastic visco-plastic self-consistent (EVPSC) model, which incorporates both slip and twinning deformation mechanisms, is used to study the lattice strain evolution in extruded magnesium alloy AZ31 under uniaxial tension and compression. The results are compared against in-situ neutron diffraction measurements done on the same alloy. For the first time, the effects of stress relaxation and strain creep on lattice strain measurements in respectively displacement controlled and load controlled in-situ tests are numerically assessed. It is found that the stress relaxation has a significant effect on the lattice strain measurements. It is also observed that although the creep does not significantly affect the trend of the lattice strain evolution, a better agreement with the experiments is found if creep is included in the simulations.

The influence of mechanical surface treatments on fatigue behavior of extruded AZ61 magnesium alloy

Abstract Surface treatments such as shot peening which introduce compressive residual stresses into the near surface region can have a beneficial effect on fatigue behavior. In the present study, tension-compression fatigue tests were carried out to understand the influence of three different mechanical surface treatments on fatigue properties of extruded AZ61 magnesium alloy at a stress ratio of −1 and frequency of 20 Hz under ambient environment. The mechanical surface treatments used in the present study were: (a) shot peening, (b) micro-peening and (c) barrel processing. It was found that the fatigue strength of shot-peened specimens actually degraded by about 30% as compared to the specimens which had not been shot peened. In the shot peened specimens cracks were nucleated at shot-peened induced surface defects which then propagated to failure, a direct indication that the shot-peening induced compressive residual stresses were not able to offset the detrimental effect of process-induced high surface roughness and surface defects. On the other hand, both micro-peened and barrel processed specimens exhibited an improvement in fatigue strength of about 15%. In these latter two instances, even though cracks were nucleated at sites of specimen surface roughness, the process-induced compressive residual stress retarded fatigue crack propagation, thereby resulting in the observed improvement in fatigue strength.

Effect of Grain Size on Fatigue Crack Propagation in Extruded AZ31 Magnesium Alloys

This paper describes the fatigue crack propagation behavior of extruded AZ31B magnesium alloys (average grain size: approximately 15 and 119 μm, respectively). Fatigue crack propagation tests were performed on center cracked tension (CCT) specimens at a stress ratio of R=0.1 and a frequency of 10 Hz at room temperature. Loading axis was parallel to the extrusion direction; crack face was perpendicular to basal plane of each grain. The crack growth rate (da/dN) of the coarse-grained specimen was approximately 5 times higher than that of the fine-grained specimen. Fracture surfaces of the fine-grained and coarse-grained specimens showed various directional steps independent of macroscopic crack growth direction.

0611 切削により加工層を付与したマグネシウム合金AZ61 押出材の疲労強度特性(GS07-2 材料力学・計算力学,オーガナイズドセッション 3:「熱・流体の可視化と計測」)

0611 切削により加工層を付与したマグネシウム合金AZ61 押出材の疲労強度特性(GS07-2 材料力学・計算力学,オーガナイズドセッション 3:「熱・流体の可視化と計測」)

The Fracture Morphology Analysis of Extruded AZ31 Magnesium Alloy under High Strain Rate Loading

The high strain rate deformation behavior of extruded AZ31 magnesium alloy were characterized by Split Hopkison Tension and Pressure Bar (SHPB and SHTB). The macro- and micro- fracture morphology of the alloy under high strain rate tension and compression loading were analyses by scanning electron microscopy(SEM) and optical microscopy(OM). The tension and compression were conducted along extrusion direction and transverse direction, respectively. The results show that the macro- fracture mode of the extruded AZ31 magnesium alloy under compression and tension are all in 45 degree along loading axis. The micro- fracture morphology of high strain rate compression and tension is of anisotropy. That is the fracture ratio of ductility to brittle of extrusion direction under high strain rate compression is much higher than that of transverse direction even if both of the fracture are mixed mode of ductile and brittle. The fracture morphology of extrusion direction under high strain rate tension is characterized by ductile, while that of transverse direction is characterized by brittle.

Dynamic behavior of extruded AZ61 Mg alloy during hot compression

Abstract The high-temperature compressive properties of an extruded AZ61 magnesium alloy were examined at different temperatures and strain rates ranging from 523 to 723 K and 1 × 10 −3 to 1 s −1 , respectively. Flow behavior analyses and microstructural observations indicated that the softening mechanism at high strain rates (or low temperatures) proceeded via a combination of the dynamic recovery (DRV) and dynamic recrystallization (DRX). The contribution of DRV to the softening effect decreased with decreasing strain rate (or increasing temperature). The stress required for the onset of DRV increased with increasing strain rate (or decreasing temperature). DRX was the dominant softening mechanism at low strain rates (or high temperatures). The constitutive equation relating flow stress, temperature, and strain rate was obtained based on the steady-state stresses. The constitutive analysis suggested that the hot deformation mechanism of the as-extruded AZ61 Mg alloy was dislocation creep controlled by lattice diffusion.

Quantification of corrosion mechanisms under immersion and salt-spray environments on an extruded AZ31 magnesium alloy

The corrosion mechanisms of pitting, intergranular, and general corrosion were examined on an extruded AZ31 magnesium alloy subjected to immersion and salt-spray environments. The three mechanisms were quantified using optical microscopy and laser profilometry for over 60 h of testing. Although both environments showed similar trends, the immersion environment was more deleterious with respect to intergranular and general corrosion. On the other hand, the salt-spray environment did allow deeper pits to form throughout the entirety of the experiments, which then led to a substantial thickness drop (general corrosion) compared with the immersion environment.

Application of Flat-Clad Optical Fiber Bragg Grating Sensor in Characterization of Asymmetric Fatigue Deformation of Extruded Magnesium Alloy

We report the application of a novel flat-cladding optical fiber Bragg grating sensor array in the characterization of low cycle fatigue deformation behavior of an extruded AZ31 magnesium alloy. The results obtained from optical fiber sensors showed strong asymmetry of stress-strain hysteresis loops, especially at high strain amplitudes, due to the occurrence of twinning in compression and detwinning in tension. At a given total strain amplitude, the degree of asymmetry of the hysteresis loops decreased with increasing number of cycles. The alloy also exhibited strong cyclic hardening at higher total strain amplitudes. All of these observations were in good agreement with those measured from an extensometer, and with those reported in the literature. In particular, the plastic strain amplitudes evaluated from optical fiber sensors demonstrated a nearly perfect agreement with those obtained from the extensometer, further corroborating the suitable use of the optical fiber sensors as an important tool in the evaluation of cyclic defromation behavior of materials.

Effects of process parameters on strength of Mg alloy AZ61 friction stir spot welds

Extruded AZ61 magnesium alloy sheets were lap-joined by friction stir spot weld (FSSW) under different welding conditions. Tool rotational speed, plunge rate, and dwell time were varied to determine their effects on the microstructure, fracture behavior, and mechanical properties of welds. Metallographic analytical results indicate that two stir zones formed in regions near the upper side and lower side of the keyhole, separately. Dynamic recrystallization occurred during the FSSW process, generating equiaxed grains in the weld region. Experiment results demonstrate that the strength of friction stir spot welds increased as bond width increased, which depended on tool speed and dwell time. An optimal combination of tool speed and dwell time can maximize the strength of joints. Under the tensile shear test, cracking started at fissure tip and extended through the partial bonding interface to the keyhole. Moreover, fracture behavior in the tensile shear test was governed mainly by bond width.

Influence of Heat Treatment on Low-Cycle Fatigue Behavior of AZ61 Magnesium Alloy

In order to identify the influence of solid solution, aging and solid solution plus aging treatments on the low-cycle fatigue behavior of the extruded AZ61 magnesium alloy, the low-cycle fatigue tests were performed at room temperature for the extruded AZ61 magnesium alloy with different treating states. The results indicate that the cyclic stress response behavior of the extruded AZ61 magnesium alloy exhibits both cyclic strain hardening and stability. The solid solution, aging and solid solution plus aging treatments tend to decrease the cyclic deformation resistance of the extruded AZ61 alloy in most conditions. The solid solution treatment can enhance the fatigue lives of the extruded AZ61 alloy at medium total strain amplitudes. In addition, the aging treatment can prolong the low-cycle fatigue lives of the AZ61 alloy at most total strain amplitudes, while the case for the solid solution plus aging treatment is just contrary. For the extruded AZ61 alloy with different treating states, a linear relationship between cyclic stress amplitude and plastic strain amplitude is noted.

Effect of twinning, slip, and inclusions on the fatigue anisotropy of extrusion-textured AZ61 magnesium alloy

In this study, experiments were conducted to quantify structure-property relations with respect to fatigue of an extruded AZ61 magnesium alloy using a MultiStage Fatigue (MSF) model. Experiments were conducted in the extruded and transverse directions under low and high cycle strain control fatigue conditions. The cyclic behavior of this alloy displayed varying degrees of twinning and slip depending on the strain amplitude as observed in the hysteresis loops of both directions. Under low cyclic conditions, asymmetrical stress strain response was observed for both orientations. However, systematic stabilization of the hysteresis occurred by half-life due to subsequent twinning and detwinning mechanisms. In addition, under high cycle fatigue, pseudo-elasticity was observed at the first and at half-life cycles. Structure-property relations were quantified by examining the fracture surfaces of the fatigued specimens using a scanning electron microscope. In terms of crack incubation, fatigue cracks were found to initiate from intermetallic particles (inclusions) that were typically larger than the mean size. Quantified sources of fatigue crack incubation, microstructurally small cracks, and cyclic stress–strain behavior were correlated to the MSF model. Based on the specific material parameters, the MSF model was able to predict the difference in the strain-life results of the AZ61 magnesium alloy in the extruded and extruded transverse directions including the scatter of the experimental results. Finally, the MSF model revealed that the inclusion size was more important in determining the fatigue life than the anisotropic effects from the texture, yield, and work hardening.