Behavior Of AZ31 Magnesium Alloy Research Articles

Deformation Behavior of AZ31 Magnesium Alloy at Elevated Temperature

Hot compression test for AZ3l magnesium alloy at deformation temperatures of 523-723K and strain rates of 0.01-10s-1 were carried out using Gleeble-3500 thermo-mechanical simulator. The experimental results show that the flow stress and microstructure vary apparently with deformation process parameters. Microstructure observations show that dynamic recrystallisation (DRX) takes place during the deformation. The characteristic with the dynamic recrystallization change with the process parameters.

Grain size and texture effects on deformation behavior of AZ31 magnesium alloy

Cold rolled AZ31 magnesium alloy sheet was subjected to friction stir processing to generate four average grain sizes ranging from 0.8 to 9.6μm. The processed material exhibited a strong basal fiber texture with the c-axis tilted about 35–55° towards the processing direction. The grain size and texture dependence of mechanical behavior were evaluated by using tensile testing along two orthogonal directions. Remarkably high ductility of ∼65% was achieved in relatively coarse grained material that fractured without developing necking when tested in the processing direction. The ductility decreased significantly to ∼10% for ultrafine grained material as the tensile yield strength increased from ∼53MPa to ∼180MPa. Grain size had limited influence on ductility of processed material tested in transverse direction, but reduced the uniform elongation to ∼2% for ultrafine grained material which exhibited ∼320MPa yield strength. Accompanying the significant anisotropy in tensile strength in two directions, the deformation of processed AZ31 in the processing direction was mainly accommodated through basal slip and extension twinning (except for ultrafine grained material); however, the deformation of material in transverse direction was dominated by non-basal slip. Influences of grain size and texture on mechanical behavior were studied in terms of work-hardening and deformation mechanisms.

Creep of AZ31 Mg alloy: A comparison of impression and tensile behavior

Creep behavior of AZ31 magnesium alloy was investigated in temperature range of 423–498K by the localized impression creep and the conventional tensile creep testing methods, in order to evaluate the correspondence of the creep results obtained by these two testing techniques. Impression creep tests were conducted under punch stresses in the range of 125–600MPa, while tensile creep tests were performed under tensile stresses in the range 35–140MPa. According to the obtained results, the creep behavior could be divided into two stress regimes with different stress exponents and activation energy values. Based on the steady-state power-law creep relationship, the average stress exponents of about 3 and 6 were, respectively, obtained at the low- and high-stress regimes in both impression and tensile creep tests. The respective average impression creep activation energies of 96.9 and 139.2kJ/mol, at the low- and high-stress regimes, were close to 93.8 and 126.6kJ/mol determined in the tensile creep tests. Based on the obtained stress exponents and activation energies, it is suggested that the dominant creep mechanism is pipe-diffusion-controlled dislocation viscous glide in the low-stress regime, and dislocation climb in the high-stress regime. The achievement of similar creep characteristics in the employed tests implies that the localized impression creep test is capable of acquiring reliable information on the creep behavior of the present wrought Mg alloy.

Stress corrosion cracking susceptibility of ultrafine grained AZ31

In this study, stress corrosion cracking (SCC) behavior of AZ31 magnesium alloy was carried out using slow strain rate testing (SSRT) technique in 3.5 wt% NaCl solution. The influence of microstructural scale on the stress corrosion behavior was investigated in AZ31 alloy with three different mean grain sizes. Single-pass and two-pass friction stir processing (FSP) was employed to obtain fine grain and ultrafine grain microstructures, respectively. For FSP, SSRT specimens were extracted from the processed region. SSRTs were carried out in air and solution at an initial strain rate of 10−6/s. A significant decrease in the ultimate tensile strength was observed for FSP specimens tested in chloride solution as compared to specimens tested in air. More than 75 % loss in total elongation was observed for the specimens tested in chloride solution as compared to the ones tested in air. In comparison with base material, lower time to failure was observed for processed samples. The higher SCC susceptibility of processed microstructure is attributed to increased hydrogen adsorption and favorable basal texture.

The correlation between the impression and double shear creep of AZ31 magnesium alloy

Abstract This study reports the application of an impression creep test to measure the creep behavior of AZ31 magnesium alloy. The correlation between the impression and double shear creep data on the same sample was determined. The creep parameters determined via impression and double shear creep assessments were found to be identical, with n = ∼3.5 and Q = ∼109.1 kJ/mol in the low-stress region, indicating that creep deformation was found to be controlled by the viscous glide of dislocations and that the viscous glide was governed by the diffusion of aluminum atoms in magnesium. The punching stress conversion factor α was determined to be 3.4 with a correlation factor β = 0.755. The Dorn constant A was determined to be 11.4 s−1. The ratio of As to Ai was 967.8, which is close to the predicted value of 928.6. This fact indicates that the impression creep relationship and double shear creep relationship can be converted into the equivalent uniaxial creep relationship.

최대하중 조건에 따른 AZ31 마그네슘합금의 실험적 피로균열전파모델 평가

It is the aim of this paper to propose the empirical fatigue crack propagation model fit to describe a crack growth behavior of AZ31 magnesium alloys. The statistical data of a crack growth for an estimation are obtained by fatigue crack propagation tests under the three cases of maximum load. The empirical models estimated are Paris-Erdogan model, Walker model, Forman model, and modified-Forman model. It is found that the empirical model fit to describe a crack growth behavior of AZ31 magnesium alloys is Paris-Erdogan model and Walker model. It is also verified that a fatigue crack growth rate exponent of a empirical model is to be a material constant.

Effect of crystal orientation on the mechanical properties and strain hardening behavior of magnesium alloy AZ31 during uniaxial compression

Abstract The effect of initial texture on the mechanical properties and strain hardening behavior of AZ31 magnesium alloy has been investigated. Cylindrical specimens of extruded and hot rolled AZ31 are compressed along different directions, with the compression axis (C) perpendicular or parallel to the extrusion direction (ED) or the sheet normal direction (ND), referred to as C⊥ED, C//ED, C⊥ND and C//ND specimen, respectively. The compression tests are conducted at room temperature with a strain rate of 0.01 s−1. The results indicate that the yield strength and the strain hardening rate are highly anisotropic with respect to the initial texture. The significant yield behavior can be induced by only a small volume of twins. When the initial grain orientations are unfavorable for { 10 1 ¯ 2 } twinning, the strain hardening rate decreases gradually. When the initial grain orientations are favorable for { 10 1 ¯ 2 } twinning, the strain hardening behavior exhibits three distinct stages. The main contribution to increasing strain hardening rate (corresponding to the stage II) results from texture strengthening, which rotates grain orientations into hard orientations by the { 10 1 ¯ 2 } twinning. The length of the stage II is predominantly related to the volume fraction of grains which are favorable for { 10 1 ¯ 2 } twinning.

Plastic deformation behavior of AZ31 magnesium alloy under multiple passes cross compression

Abstract Plastic deformation behavior of hot-rolled AZ31 Mg alloy under 6 passes plane strain compression along transverse direction (TD) and normal direction (ND) alternatively is systematically study in current paper. With 10% compression along TD, most grains are nearly twinned totally and extension twinning takes place during subsequent compression along ND. Yield stress rises with increased compression passes due to enhanced activation stress for extension twinning by dislocations generated in previous pass of compression. Preferred distribution of prismatic planes appears after each pass of compression besides of the rotation of basal plane poles toward compression axis, which is closely related with extension twinning.

Superplasticity of AZ31 magnesium alloy prepared by friction stir processing

Microstructure and tensile behaviors of AZ31 magnesium alloy prepared by friction stir processing (FSP) were investigated. The results show that microstructure of the AZ31 hot-rolled plate with an average grain size of 92.0 μm is refined to 11.4 μm after FSP. The FSP AZ31 alloy exhibits excellent plasticity at elevated temperature, with an elongation to failure of 1050% at 723 K and a strain rate of 5×10 −4 s −1. The elongation of the FSP material is 268% at 723 K and 1×10 −2 s −1, indicating that high strain rate superplasticity could be achieved. On the other hand, the hot-rolled base material, which has a coarse grain structure, possesses no superplasticity under the experimental conditions.

Effects of grain size, texture and twinning on mechanical properties and work-hardening behavior of AZ31 magnesium alloys

Abstract Rolled sheets with various microstructures and (0 0 0 2) pole intensities have been obtained successfully using conventional flat rolling (CFR), differential speed rolling (DSR) and heat treatment methods. The mechanical properties of AZ31 magnesium alloys with different grain sizes, basal texture intensities and twinning conditions were investigated at room temperature. It was found that the rolled sheets show good ductility when grain size is around 15 μm. Finer grains and random (0 0 0 2) basal intensity are hardly achieved simultaneously using both DSR-RS and CFR-AR processing methods in current study. In the determination of the rolling processing, it is important to consider preferred grain refinement or lowered basal texture intensity. Moreover, the influences of grain size, basal texture intensity and twinning conditions on work-hardening rate were examined as well. As grain size decreases, extrapolated work-hardening rate decreases; while basal texture intensity has little effect on it. On the other hand, twinning plays a vital role in decreasing work-hardening in plastic flow stage; while twin boundaries increase the work-hardening rate in easy glide stage and linear hardening stage. However, they drop faster than un-twinned samples in stage III when the true strain is higher than 0.06.

Effect of impurity reduction on rollability of AZ31 magnesium alloy

The effect of impurity reduction on the hot rolling behavior of AZ31 magnesium alloy was systematically investigated in this study. In the as-cast alloys, the total content of main impurity elements such as Fe, Si, Cu, and Ni was varied from 0.0462 to 0.0163 wt% by changing the purity of used raw magnesium metals. The alloys after homogenization were subjected to hot rolling at 300 °C with a reduction of 20% per pass. It was found that the initiation of edge cracks is postponed with reducing impurity level in the alloys. And the maximum rolling reduction prior to edge cracking increases from 34 to 58% as the impurity content drops from 0.0462 to 0.0163 wt%. Microstructural observations showed that smaller grains are present in the alloy with lower impurity content in the cast and homogenization states. Moreover, decreasing impurity content leads to a reduced number of deformation twins and an enhanced volume fraction of small recrystallized grains in the as-rolled microstructure, which indicates that impurity reduction is beneficial to the recrystallization process and subsequent plastic deformation. Based on the results, the enhancement in hot rollability of the AZ31 sheet by impurity reduction should be due to finer grain size, the reduced number of deformation twins and the enhanced extent of recrystallization.

The Application of Shear Compression Specimen to Study Shear Deformation Behavior of AZ31 Mg Alloy at High Temperatures and Quasi-Static Regime

In the present work, shear-compression specimen was successfully employed to study the shear flow behavior of AZ31 magnesium alloy at high temperatures and in quasi-static regime. The loading process of shear-compression testing was simulated using ABAQUS software. This was carried out in the temperature range of 250–450°C and displacement rates of 1.5, 15 and 150 mm/min. In addition, to validate the numerical simulation results, the shear compression specimens were also compressed experimentally at the same conditions of numerical ones. Equivalent stress–strain curves obtained from numerical simulation results along with microstructural observations were utilized to investigate the effect of loading conditions on deformation behavior of the experimental alloy. The results indicated a homogenous distribution of shear strains within the gage and the high applicability of shear-compression specimen to study shear flow behavior of materials at hot deformation conditions.

Galvanic Corrosion Behavior and Three Protection Techniques of Magnesium Alloy Coupled to A6N01S-T5 Aluminum Alloy in NaCl Solution

In this work, the galvanic corrosion behavior of AZ31 magnesium alloy in contact with A6N01S-T5 aluminum alloy in NaCl solution was investigated by electrochemical method, the salt immersion method, SEM. And three protection techniques: (a) rubber gasket technique ,(b)organic coating technique and (c) anodizing technique were used to inhibit the galvanic corrosion. The results of open circuit potential and polarization curve method were explained the corrosion behavior of AZ31 and A6N01S-T5.It was found that AZ31 as anode was accelerated corrosion and A6N01S-T5 as cathode was also corrode in salt immersion experiment. With the increasing of immersion time, the corrosion rate of AZ31 and A6N01S-T5 was gradually decreasing. Then, the efficacy of different anti-corrosive technologies was compared. Fluorine coating technique was an effective way to protect Mg alloy and Al alloy. It was possible to guide the anti-corrosion of magnesium alloy in mobile industry.

Characterization of High‐Strain Rate Mechanical Behavior of AZ31 Magnesium Alloy Using 3D Digital Image Correlation

AbstractCharacterization of the material mechanical behavior at sub‐Hopkinson regime (0.1 to 1 000 s−1) is very challenging due to instrumentation limitations and the complexity of data analysis involved in dynamic loading. In this study, AZ31 magnesium alloy sheet specimens are tested using a custom designed servo‐hydraulic machine in tension at nominal strain rates up to 1 000 s−1. In order to resolve strain measurement artifacts, the specimen displacement is measured using 3D Digital Image correlation instead from actuator motion. The total strain is measured up to ≈ 30%, which is far beyond the measurable range of electric resistance strain gages. Stresses are calculated based on the elastic strains in the tab of a standard dog‐bone shaped specimen. Using this technique, the stresses measured for strain rates of 100 s−1 and lower show little or no noise comparing to load cell signals. When the strain rates are higher than 250 s−1, the noises and oscillations in the stress measurements are significantly decreased from ≈ 250 to 50 MPa. Overall, it is found that there are no significant differences in the elongation, although the material exhibits slight work hardening when the strain rate is increased from 1 to 100 s−1.

Effect of High-Intensity Pulsed Ion Beam Irradiation on the Electrochemical Corrosion Behavior of AZ31 Magnesium Alloy

HIPIB irradiation experiment is carried out at a specific ion current density of 1.1 J/cm2 with shot number from one to ten in order to explore the effect of shot number on electrochemical corrosion behavior of magnesium alloy. Surface morphologies, microstructure and corrosion resistance of the irradiated samples are examined by scanning electron microscopy (SEM), transmission electron microscope (TEM) and potentiodynamic polarization technique, respectively. It is found that HIPIB irradiation leads to the increase in open circuit potential, corrosion potential and breakdown potential, and the decrease in the corrosion current density and the corrosion rate as compared to the original sample. The improved corrosion resistance is mainly attributed to the grain refinement and surface purification induced by HIPIB irradiation.

Effects of ultrasonic vibration on plastic deformation of AZ31 during the tensile process

An investigation on the plastic behavior of AZ31 magnesium alloy under ultrasonic vibration (with a frequency of 15 kHz and a maximum output of 2 kW) during the process of tension at room temperature was conducted to reveal the volume effect of the vibrated plastic deformation of AZ31. The characteristics of mechanical properties and microstructures of AZ31 under routine and vibrated tensile processes with different amplitudes were compared. It is found that ultrasonic vibration has a remarkable influence on the plastic behavior of AZ31 which can be summarized into two opposite aspects: the softening effect which reduces the flow resistance and improves the plasticity, and the hardening effect which decreases the formability. When a lower amplitude or vibration energy is applied to the tensile sample, the softening effect dominates, leading to a decrease of AZ31 deformation resistance with an increase of formability. Under the application of a high-vibrating amplitude, the hardening effect dominates, resulting in the decline of plasticity and brittle fracture of the samples.

Corrosion behavior of AZ31 magnesium alloy in simulated acid rain solution

The corrosion mechanism of AZ31 magnesium alloy used as automobile components and the influence of the concentration of Cl − ion in simulated acid rain (SAR) were studied by electrochemical tests and SEM. The results show that pitting corrosion happens around the AlMn phases locating at the grain boundary. The corrosion of AZ31 magnesium alloy in SAR is controlled by the rate of anodic dissolution and hydrogen evolution, and the corrosion rate of AZ31 increases with increasing concentration of Cl − ion. However, the Cl − ion in SAR is not the main influencing factor inducing the pitting corrosion.

Compressive deformation behavior of AZ31 magnesium alloy under quasi-static and dynamic loading

Compressive properties of AZ31 alloy were investigated at temperatures from room temperature to 543 K and at strain rates from 10 −3 to 2×10 4 s −1. The results show that the compressive behavior and deformation mechanism of AZ31 depend largely on the temperature and strain rate. The flow stress increases with the increase of strain rate at fixed temperature, while decreases with the increase of deformation temperature at fixed strain rate. At low temperature and quasi-static condition, the true stress-true strain curve of AZ31 alloy can be divided into three stages (strain hardening, softening and stabilization) after yielding. However, at high temperature and high strain rate, the AZ31 alloy shows ideal elastic-plastic properties. It is therefore suggested that the change in loading conditions (temperature and strain rate) plays an important role in deformation mechanisms of AZ31 alloy.

Dry sliding tribological behavior of AZ31 magnesium alloy irradiated by high-intensity pulsed ion beam

The dry sliding tribological behavior of AZ31 magnesium alloy irradiated by high-intensity pulsed ion beam (HIPIB) at energy density of 3.4 J/cm 2 with 10 shots is investigated by dry sliding wear tests in order to explore the effect of HIPIB irradiation on tribological property of magnesium alloy. Surface morphologies, composition and structure of the irradiated AZ31 magnesium alloys are examined by electron probe microanalysis (EPMA) and X-ray diffraction (XRD). The results indicated that HIPIB irradiation led to the increase in surface microhardness and the reduction in friction coefficient and wear rate. Wear rate for both the original and the irradiated samples increased with increasing sliding load from 0.1 to 0.5 N. The transition from severe metallic wear to mild oxidative wear induced by HIPIB irradiation was observed by a combined analysis in surface morphology and chemical composition of wear tracks, mechanically mixed materials and wear debris, which is mainly attributed to the significant increase in microhardness resulting from grain refinement on the irradiated surface. In addition, defects induced by HIPIB irradiation promoted the diffusion of oxygen during sliding wear and therefore led to the formation of compact mixed materials and protective films on the wear tracks surface, which also contributes to the transition in wear mechanism of AZ31 magnesium alloy induced by HIPIB irradiation.

Influence of chloride, sulfate and bicarbonate anions on the corrosion behavior of AZ31 magnesium alloy

Influence of chloride, sulfate and bicarbonate anions on the corrosion behavior of AZ31 magnesium alloys in dilute solutions was investigated by electrochemical measurements, whereby corrosion maps in terms of electrode potential and solution concentration were obtained. AZ31 alloy exhibited corrosion and passivation zones in those dilute solutions. The passivation zone was strongly influenced by the kinds of the solution used and the broadest zone was obtained in Na 2SO 4, followed by NaCl and NaHCO 3. AZ31 alloy had a better corrosion resistance in Na 2SO 4, attributing to the lowest attack by SO 4 2− and a thick corrosion product covering the surface which inhibited the corrosion attack. However, despite a much lower passivation zone in NaHCO 3 as compared to the other two solutions, the corrosion rate in NaHCO 3 was found to be the lowest. The values of open-circuit potential were in the passivation zone when [Cl −] was less than 0.2 mol/L in NaCl, and [SO 4 2−] and [HCO 3 −] were both less than 0.3 mol/L in Na 2SO 4 and NaHCO 3. In the passivation zone, the formation of surface films or corrosion products on the material surface retarded further corrosion in dilute solutions. In the corrosion zone, pits grew continuously in depth and diameter in NaCl and Na 2SO 4 resulting in the localized corrosion through the agglomeration of pits. The formation of crystalline-like MgCO 3 products exhibited the general corrosion in NaHCO 3.