Behavior Of AZ31 Magnesium Alloy Research Articles

Study on anisotropic mechanical behavior of AZ31 magnesium alloys under free-end torsion

In this study, the mechanical behavior and microstructure of a hot-rolled AZ31 magnesium alloy sheet under free-end torsion with torsional axis along rolling direction (RD), normal direction (ND) and 45° in ND-RD plane, have been investigated both experimentally and numerically. The mechanical behavior under torsion, including stress-strain response, Swift effect and strain hardening rate, present obvious anisotropy. The Swift effect is sensitive to the direction of torsion axis and exhibits remarkable anisotropy with axial elongation in ND sample and axial shortening in RD and 45° samples. The axial elongation or shortening is determined by both slips and extension twin, with extension twin exerting a greater influence on the extent of the axial deformation. During shear straining, the dominant deformation mode transforms basal slip to prismatic slip with the axial direction deviating from ND to RD, while the second-order pyramidal ⟨c+a⟩ slip is nearly not activated during whole deformation attributed to its high critical resolved shear stress. Based on the effective Schmid factor (ESF) of deformation modes, the grains with favored orientation would get activation of {101‾2} extension twin due to the high ESF, resulting in the different twin volume fractions. Additionally, the activation of twin relative to basal slip has a connection with the increasing trend of normalized strain hardening rate.

Effect of Single and Co-addition of Rare Earth on the Microstructure, Mechanical Properties, and Corrosion Behavior of AZ31 Magnesium Alloys

Effect of Single and Co-addition of Rare Earth on the Microstructure, Mechanical Properties, and Corrosion Behavior of AZ31 Magnesium Alloys

Effect of degradable (CaP and ZnO) nanoparticals void-plugging MgFe-LDHs film on the pitting-responsive behaviors of AZ31 magnesium alloy

The influence of degradable (CaP and ZnO) nanoparticles embedded in MgFe-LDHs film on protective-barrier and pitting-responsive behaviors of magnesium alloy were investigated. Cyclic-polarization studies in SBF indicated that LDHs/ZnO exhibited lower pitting-resistance but higher re-passivation ability compared to LDHs/CaP. Unexpectedly, different self-repairing effects and corroded-morphologies were observed after immersion in SBF. For LDHs/CaP, the additional layer induced by CaP shielded the intact film from corrosive-attacking, yielding tunnel-shaped corroded-channels. For LDHs/ZnO, the secondary zinc-containing layer covered corroded-pits by dissolution/recrystallization, retarding Cl− vertical attack to form shallow pits. In brief, the secondary-protective layer interferes with Cl− selective attack, governing the pitting propagation.

Environment-assisted cracking of AZ31 magnesium alloy in a borate buffer solution containing ammonium thiocyanate under various potentials

The environment-assisted cracking behavior of AZ31 magnesium alloy was investigated using tensile tests at cathodic and corrosion potentials in a Na2B4O7∙10H2O solution containing NH4SCN and in air. Although the mechanical properties of the AZ31 with an initial strain rate of 10−4 s−1 were independent of the environments, those degraded in the solution with an initial strain rate of 10−6 s−1. The total elongation became smaller at higher potentials. The average hydrogen absorption rate increased with a positive potential shift. These facts imply that environment-assisted cracking became more severe under relatively high potential owing to corrosion accompanied by enhanced hydrogen absorption.

Influence of Groundnut Shell Ash Particle (GSAp) Addition on Mechanical and Corrosion Behaviour of AZ31 Magnesium Alloy

Magnesium based alloys are some of the widely used light weight metals in vehicles and aerospace industries, but these materials are having low strength to weight ratio when compared to aluminium. To enhance their strength to weight ratio, some ceramic materials like carbides and oxides of metals are added as reinforcements. In this work, AZ31 magnesium alloy is reinforced with 1%, 2% and 3% of Groundnut Shell Ash particles (GSAp) through powder metallurgy. Micro hardness and compressive strength are studied and the microstructural analysis is also done. The addition of ash particles as reinforcement has not shown much variation in the strength and hardness. The addition of ash particles of more than 3% leads to crack. The addition of ash particles increases the rate of corrosion.

Effect of Recrystallization Behavior of AZ31 Magnesium Alloy on Damping Capacity

For a wide industrial application of magnesium alloys, a method for imparting high damping properties while maintaining mechanical properties is required. Controlling the crystallographic texture seems to be useful, because dislocations are known to have a significant influence on the damping characteristics of magnesium alloys. In addition, textures are affected by the microstructure and texture variation when the deformation or annealing is applied. However, there were less reports about their effect on damping capacity. Therefore, the effect of twinning and annealing, which can affect the recrystallization, were investigated in this study. An AZ31 alloy was hot rolled at 673 K with a reduction ratio of 10% and 50%, and then annealed at 673 K and 723 K for 0.5, 1, 2, and 3 h, respectively. SEM-EBSD was used to examine the microstructure and texture. In addition, each specimen's hardness and internal friction were contemporarily measured. As a result, hot rolling produced tensile twins and their fraction increased with internal friction when the reduction ratio increased. Due to annealing, a discontinuous type of static recrystallization occurred within the twinning grains, and was highly activated along with the increasing annealing temperature and the fraction of twinning. In the samples annealed at 723 K, the internal friction continuously increased over the annealing time, whereas in the samples annealed at 673 K, the decrease in dislocation density was delayed while the internal friction showed a relatively low value.

Tensile fracture prediction of AZ31 cast-rolled sheet based on hot working map

Uniaxial thermal tensile testing at a wide temperature range (473–723 K) and strain rate (0.01-1s−1). The isothermal hot tensile deformation and fracture behavior of AZ31 magnesium alloy in cast-rolled state was investigated using the Gleeble-3800 thermomechanical simulator. Based on the real stress-strain data, the thermal processing diagrams of the isothermal hot tensile tests were established. The effects of deformation parameters on strain hardening rate, microstructure evolution and fracture form in hot tensile tests were investigated. The results showed that the rheological stress increases with increasing strain rate and decreases with increasing deformation temperature. The optimum process parameters for the cast-rolled state of AZ31 Mg alloy were determined from the thermal processing diagram. With increasing temperature and decreasing strain rate, the transformation of deformation mechanism and fracture type in magnesium alloy is closely related to the deformation of twinned and recrystallized structure.

Effect of Friction Stir Processing on the Fatigue Performance of AZ31 Magnesium Alloy

Herein, the cyclic mechanical behavior of AZ31 magnesium alloy after multipass friction stir processing (FSP) is investigated up to the very high‐cycle fatigue (VHCF) regime. The grain refinement and texture evolution after processing are evaluated to enhance the understanding of the fatigue response. Although ultimate tensile strength and ductility of the friction stir processed AZ31 increase up to about 320 MPa and 25%, respectively, the fatigue performance deteriorates in comparison with that of the as‐received condition due to the low yield strength and texture evolution after processing. Furthermore, analysis of fracture surfaces of the samples after cyclic loading reveals that the as‐received AZ31 is more prone to brittle fracture with multiple‐origin fatigue failure even at low stress amplitudes. On the contrary, the dominant failure mechanisms of the friction stir processed samples are initiation and propagation of cracks originating from the surface, porosities, and grain size inhomogeneity. Nevertheless, the capability of FSP for providing superior crack initiation resistance in the VHCF regime is demonstrated as a significant contribution. Based on a detailed study of prevalent microstructural features, processing–property–damage relationships are established indicating the major effect of FSP on the final performance of the AZ31 magnesium alloy.

Effect of grain refinement induced by wire and arc additive manufacture (WAAM) on the corrosion behaviors of AZ31 magnesium alloy in NaCl solution

Abstract Additive manufacturing (AM) of Mg alloys has become a promising strategy for producing complex structures, but the corrosion performance of AM Mg components remains unexploited. In this study, wire and arc additive manufacturing (WAAM) was employed to produce single AZ31 layer. The results revealed that the WAAM AZ31 was characterized by significant grain refinement with non-textured crystallographic orientation, similar phase composition and stabilized corrosion performance comparing to the cast AZ31. These varied corrosion behaviors were principally ascribed to the size of grain, where cast AZ31 and WAAM AZ31 were featured by micro galvanic corrosion and intergranular corrosion, respectively.

Processing, microstructure, and mechanical behavior of AZ31 magnesium alloy fabricated by electron beam additive manufacturing

In this work, AZ31 magnesium alloy was successfully manufactured by the electron beam additive manufacturing (EBAM) technique. The microstructure and mechanical properties of the EBAM samples under different energy densities and deposition passes were analyzed. The results show that the energy density has a decisive effect on the manufacturability of the sample, wherein the sample prepared at an energy density of 1.432 × 1010 J·m-3 possesses the best manufacturability. The thermal cycling of the EBAM technique resulted in apparent grain size variation and layered arrangement along the deposition height. The fine grains with an average size of approximately 20 µm account for 30% of the sample while the remaining coarse grains possess an average size of approximately 40 µm. Moreover, a large number of fine Al8Mn5 and Mg17Al12 phases precipitated due to the high cooling rate of the molten pool. The microhardness of the sample first decreased and then increased slightly with increasing deposition height. Under the combined effects of dispersion strengthening and grain refinement, the EBAM specimens demonstrated excellent tensile strength and elongation of 230 MPa and 13.5%, respectively, which are superior to those of the die-cast AZ31 alloy.

Research on Dynamic Marine Atmospheric Corrosion Behavior of AZ31 Magnesium Alloy

The dynamic marine atmospheric corrosion behavior of AZ31 magnesium alloy was investigated in situ exposed on the deck of marine scientific research vessel for 1 year. The marine scientific research vessel carried out five voyages from the coast of China to the western Pacific Ocean, while the navigation track and environmental data were collected and analyzed. The corrosion rate and characteristics were evaluated by using weight loss tests, scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and electrochemical measurements. The corrosion rate from weight loss values was 52.23 μm∙y−1 after exposure for 1 year, which was several times higher than that of the static field exposure test in marine atmospheric environment of other reported literature. The main corrosion products were Mg5(CO3)4(OH)2·4H2O, MgCO3·3H2O and Mg2(OH)3Cl·4H2O. The corrosion was initiated from pitting corrosion and evolved into general corrosion gradually. The serious corrosion maybe due to the harsh corrosive environment with alternating changes in temperature and relative humidity caused by multiple longitude and latitude changes, and particularly high deposition rate of chloride during voyage, which was nearly twenty times that on the coast of China. This study provides effective data for the application of magnesium alloy in shipboard aircraft and other equipment, and provides a reference for indoor simulation experiments.

Tribological behaviour of AZ31 magnesium alloy reinforced by bimodal size B4C after precipitation hardening

Abstract This study investigated dry sliding wear properties of AZ31 magnesium alloy and B4C-reinforced AZ31 composites containing 5, 10, and 20 wt.% B4C with bimodal sizes under different loadings (10–80 N) at various sliding speeds (0.1–1 m/s) via the pin-on-disc configuration. Microhardness evaluations showed that when the distribution of B4C particles was uniform the hardness of the composites increased by enhancing the reinforcement content. The unreinforced alloy and the composite samples were examined to determine the wear mechanism maps and identify the dominant wear mechanisms in each wear condition and reinforcement content. For this purpose, wear rates and friction coefficients were recorded during the wear tests and worn surfaces were characterized by scanning electron microscopy and energy dispersive X-ray spectrometry analyses. The determined wear mechanisms were abrasion, oxidation, delamination, adhesion, and plastic deformation as a result of thermal softening and melting. The wear evaluations revealed that the composites containing 5 and 10 wt.% B4C had a significantly higher wear resistance in all the conditions. However, 20 wt.% B4C/AZ31 composite had a lower resistance at high sliding speeds (0.5–1 m/s) and high loadings (40–80 N) in comparison with the unreinforced alloy. The highest wear resistance was obtained at high sliding speeds and low loadings with the domination of oxidative wear.

Influence of ammonium sulfate on the corrosion behavior of AZ31 magnesium alloy in chloride environment

Electrochemical corrosion of AZ31 magnesium alloy in the NH4+-SO42−-Cl− environment is studied. Effect of NH4+ overshadows that of Cl− as the (NH4)2SO4 concentration is 0.005 M or higher, yielding an evolution from localized corrosion to uniform corrosion. Acceleration effect of NH4+ can be attributed to that (i) NH4+ dissolves the inner MgO and hinders the precipitation of Mg(OH)2 and (ii) the buffering ability of NH4+ provides H+, enhances the hydrogen evolution, and expedites the corrosion process. The latter is demonstrated as the dominant factor with the results in unbuffered and buffered environments. The severe corrosion and hydrogen process in NH4+-containing solution results in a high Hads coverage and yields an inductive loop within the low frequency. Meanwhile, SO42− is helpful in generating cracked but partially protective corrosion products, while Cl− could broaden the corrosion area beneath the corrosion product.

Improving stress corrosion cracking resistance of AZ31 magnesium alloy in Hanks’ solution via phosphate conversion with laser shock peening pretreatment

The present work aims to improve stress corrosion cracking (SCC) behavior of AZ31 magnesium alloy in Hanks’ solution via laser shock peening (LSP) and subsequent phosphate conversion (PC). The surface and cross section morphology, microstructure and scratch behavior of coated samples were characterized with and without LSP pretreatment. Additionally, immersion, electrochemical corrosion and stress corrosion tests in Hanks’ solution were conducted to evaluate the suitability of LSP and PC composite processing for improving corrosion resistance and the stress corrosion susceptibility of AZ31 magnesium alloy in Hanks’ solution. The experimental results showed that the grain refinement and high specific area generated by LSP promoted the deposition of coating and then improved the scratch resistance of coating. The LSP/PC composite coating significantly enhanced the corrosion resistance and mechanical properties of AZ31 magnesium alloy in Hanks’ solution, which was attributed to the dense coating formed by PC reaction and the strain strengthened layer induced by LSP pretreatment on the sub-surface of the material.

Corrosion behavior of AZ31 magnesium alloy with calcium addition

The effect of calcium on microstructure and corrosion characteristics of AZ31 was investigated. Electron probe microanalysis, scanning electron microscopy and electron back-scattered diffraction were employed for microstructural analysis. Corrosion behavior was characterized by open circuit potential, potentiodynamic polarization and electrochemical impedance spectroscopy in NaCl at different pH levels. Microstructural observations confirmed the formation of (Mg,Al)2Ca in AZ31–0.5Ca. The corrosion rates were 84.21 mpy/ 31.71 mpy and 23.42 mpy/ 9.40 mpy for AZ31 and AZ31–0.5Ca at pH 6 and pH 11, respectively. Improved corrosion resistance was attributed to segregation of aluminum with calcium to form (Mg,Al)2Ca which reduced β-Mg17-Al12 area fraction.

Biaxial Deformation Behavior of Az31 Magnesium Alloy Along Rd and Diagonal Direction Degree between Td and Nd

Biaxial Deformation Behavior of Az31 Magnesium Alloy Along Rd and Diagonal Direction Degree between Td and Nd

Processing, Microstructure, and Mechanical Behavior of Az31 Magnesium Alloy Fabricated by Electron Beam Additive Manufacturing

Processing, Microstructure, and Mechanical Behavior of Az31 Magnesium Alloy Fabricated by Electron Beam Additive Manufacturing

Dry sliding wear behaviour of AZ31 magnesium alloy strengthened by nanoscale SiCp

In this work, the wear and friction behavior of nanoscale SiCp (1 vol.%) reinforced Mg composite were investigated. Experiments were carried out by rubbing a GCr15 steel ball on the surface of pin specimens with the different sliding velocities of 0.1, 0.3 and 0.5 m/s at distinctive normal loads of 10, 20, and 30 N, respectively (without the aid of lubricant). Detailed analysis demonstrated that SiCp efficiently block the grain growth and improve the mechanical properties of the composite due to grain refining and dislocation strengthening. As a result, the wear resistance of composite was more prominent s compared with the initial alloy under all test condition. With the increase of sliding speed or load, the wear rate of composite increases gradually. The wear rate is reduced by 12% compared to the alloy, particularly in high load condition. Under low speeds, abrasive wear and slight oxidative wear were prevalent. Subsequently, the wear mechanism transitions to the initial delamination wear as the sliding speed increases. Severe plastic deformation occurs on the surface of the friction sample under high load, and the surface damage is serious.

Numerical study on the plastic deformation behavior of AZ31 magnesium alloy under different loading conditions

Based on the stress characteristics of the instantaneous cross-section deformation of the wall reducing section during the cold rolling of two-roll Pilger pipes, the rectangular samples with 0° and 90° to the extrusion direction (ED) were cut from the extruded AZ31 magnesium alloy bar for 3% pre-deformation test to simulate its stress state equivalently. The sample was then cut from the pre-deformed sample by wire cutting for secondary compression, and the sample that is not pre-deformed is selected. The mechanical behavior and texture evolution of AZ31 magnesium alloy under different loading conditions were respectively studied by EBSD experiment and VPSC simulation. Results show that the true stress–strain curve and texture evolution characteristics of AZ31 magnesium alloy during the secondary compression process are in good agreement with the prediction of the VPSC model. The secondary compression behavior can be effectively explained by the relative activity of the deformation modes. The pre-deformation in the ∥ED (⊥ED) direction is conducive to the shift of the pole density of the {0001} basal surface texture to the positive and negative directions of the ED (TD). The pre-deformed sample exhibits a higher yield strength than the non-pre-deformed sample in the same loading direction. The high ductility of magnesium alloys can be achieved by activating pyramidal 〈c + a〉 slippage.

Corrosion behavior of AZ31 magnesium alloys coated with PMMA/HA as biodegradable implants

Magnesium alloys' rapid corrosion rates have limited their use as biodegradable implants. As a result, designing a composite coating to slow the corrosion of the AZ31 magnesium alloy is critical. A spin coating process was used to cover an AZ31 alloy with a polymethylmethacrylate (PMMA)/hydroxyapatite (HA) composite coating. The coating characteristics was estimated using AFM, FESEM contact angle, and antibiofilm formation. In addition, potentiodaynamic polarisation and hydrogen evolution measurements were used to assess the coating's corrosion resistance and degradation behavior. In general, corrosion experiments revealed that specimens coated with one or two layers of PMMA polymer were successful in slowing down the rate of corrosion in Ringer's solution. Adding hydroxyapatite particles to the PMMA polymer also considerably reduces the rate of corrosion. Furthermore, the corrosion resistance of the coating with two layers of coatings is greatly improved.