Behavior Of AZ31 Magnesium Alloy Research Articles

Influence of Uric Acid on the Corrosion Behavior of AZ31 Magnesium Alloy in Simulated Body Fluid

Influence of Uric Acid on the Corrosion Behavior of AZ31 Magnesium Alloy in Simulated Body Fluid

Low cycle fatigue behavior of AZ31 magnesium alloy joined by friction stir welding

AbstractThis study, aims to weld the 5.2 mm thick AZ31 magnesium alloy with conventional friction stir welding at the highest joining efficiency. As a result of the experiments, 88% joining efficiency in tensile strength has been obtained at 1250 rpm, 400 mm.min−1 welding parameter. As a result of micro–macrostructure photographic examinations of the samples joined with these parameters, it is seen that the joining is fully realized. Samples joined with these parameters have been used in fatigue tests. According to the strain‐controlled low cycle fatigue test results performed on welded and base metal samples, the base metal samples have exceeded the 50,000‐cycle limit without failure, with an elongation rate of 0.3%, and the welded samples with an elongation rate of 0.2%. Low cycle fatigue parameters of welded and base metal samples have been obtained according to the Coffin‐Manson‐Basquin equation.

Understanding the mechanism of bimodal texture evolution and DRX behavior of AZ31 magnesium alloy during shear deformation

Shear deformation in commercial magnesium alloys frequently resulted in an additional atypical texture where the basal plane aligned nearly parallel to the extrusion direction, affecting the alloy's mechanical anisotropy. This study prepared AZ31 magnesium alloys with both typical shear texture and atypical texture using a two-stage shear method at 250 °C, 290 °C, and 340 °C. The formation mechanism of the bimodal texture and their relationship with dynamic grain refinement and deformation parameters were comprehensively investigated. While temperature-dependent activation of <c+a> slip usually contributed to the atypical texture, this study identified a {101¯2} twin associated microstructure that reinforced the abnormal texture at lower processing temperature. It was found that the abundant nucleation of the multi-orientation {101¯2} twin bands in the initial stage and their differential slip activations facilitated the evolution of an alternating banded structures characterized by bimodal texture. These microstructures inherited the grain boundary rotation axis of {101¯2} twin and was potentially assimilated into specialized θ[112¯0] symmetric tilt grain boundaries with lower interface energy during continuous shear, stabilizing the bimodal texture. During shear deformation, grain nucleation strengthened the [101¯0]−[112¯0] fibers with bimodal texture by generating ∼30°[0001] grain boundaries through the preferential accumulation of prismatic dislocations. However, more continuous dynamic recrystallization, discontinuous dynamic recrystallization, and micro-shear bands facilitated the nucleation of grains with dispersed basal orientations via dominant non-prismatic dislocations, weakening the overall texture. Besides, the mechanical anisotropy of the alloys was comprehensively influenced by atypical texture and microstructure. At higher deformation temperatures, the reduction in twinning bands and the increase in dynamic recrystallization level relieved the alloy’s tension-compression asymmetry, but deprived its yield strength. This study supplemented the formation mechanisms of bimodal texture during shear deformation, providing valuable insights for optimizing wrought magnesium alloys with superior mechanical properties.

Effect of sliding speed and sliding distance on wear behavior of AZ31-B4C composite

Emphasis of current research is to investigate the dry sliding behavior of AZ31 magnesium alloy and AZ31–1.5B4C magnesium metal matrix composites (MMCs) at varying sliding speeds and sliding distances. Magnesium alloy and composite are fabricated through ultrasonic assisted stir casting method. Optical microscope (OM), scanning electron microscopy (SEM), and energy dispersive x-ray analysis (EDAX) are used to characterize developed materials. Microhardness of all materials is measured using a Vickers microhardness tester. Wear-friction behavior is investigated in dry sliding mode using pin-on-disc tribometer at room temperature. Magnesium alloy and composite are tested over a range of sliding speeds (0.25–1.25 m s−1) and distances at a moderate normal load (20N). Wear morphology is finally investigated for composites and alloy under SEM and EDAX. SEM micrographs of as-cast AZ31-1.5B4C composite reveals uniform distribution of B4C particles with noticeable refinement in grain structure. EDAX spectra of AZ31-1.5B4C composite depict the presence of boron and carbon along with existing elements of AZ31 alloy. Microhardness has enhanced around 30% for Mg-MMC by incorporating 1.5 wt% B4C in AZ31 alloy. Furthermore, the use of B4C as reinforcement increases the density of the composite. Wear rate is reduced by around 20% and COF is reduced by around 25% for AZ31-1.5B4C composite compared to AZ31 alloy for all experimental conditions. Abrasion, oxidation, adhesion and delamination wear mechanisms are observed as dominant mechanism for varying sliding speeds and distances.

Deformation Behavior of AZ31 Magnesium Alloy with Pre-Twins under Biaxial Tension.

In the present study, the mechanical response and deformation behavior of a Mg AZ31 plate with different types of pre-twins was systematically investigated under biaxial tension along the normal direction (ND) and transverse direction (TD) with different stress ratios. The results show that significant hardening was observed under biaxial tension. The yield values in the direction of larger stress values were higher than those under uniaxial loading conditions, and the solute atom segregation at twin boundaries generates more obvious strengthening effect. Noting that, for TRH (with cross compression along the rolling direction (RD) and TD and annealing at 180 °C for about 0.5 h) sample, the strength effect of the RD yield stress σRD:σND = 2:1 was higher than that of the ND yield stress under stress ratio σRD:σND = 1:2. There is a complex competition between twinning and detwinning under biaxal tension along the ND and TD of the pre-twinned samples with the variation in the stress ratio along the TD and RD. The variation in the twin volume fractions for all samples under biaxial firstly decreases and then increases with a higher stress ratio along the ND. As for the TDH sample (precompression along the TD and annealing), the changes of the twin volume fraction were lower than that of the TR sample (cross compression along the TD and RD). However, the amplitude of variation in twin volume fraction of the TRH sample is higher than that of the TR sample. This is because the relative activity of detwinning decreases and that of twinning increases, as the ND stress mainly leads to the growth of pre-twins and the TD stress often promotes detwinning of primary twins. With a higher stress ratio along the ND, the activity of twinning deformation increases and that of detwinning decreases.

Effect of strain on the adiabatic shear behaviour of AZ31 magnesium alloy

The effect of strain on the adiabatic shear behaviour of AZ31 magnesium alloy under high strain rate compression was studied using split Hopkinson pressure bar (SHPB). The microstructure of the specimen was characterised using optical microscopy and electron backscatter diffraction. The results indicate that the adiabatic shear sensitivity increased with the strain. The microstructure evolution of adiabatic shear deformation has been investigated. Firstly, a large number of twins and dislocations are formed and accumulate in the early stage of deformation. Subsequently, they transform into dynamic recrystallised grains, forming an adiabatic shear band (ASB) and ultimately leading to crack formation. The dynamic recrystallisation mechanism in the ASB involves twinning-induced dynamic recrystallisation (TDRX) and rotational dynamic recrystallisation (RDRX). This study has analysed the ASB mechanism, which provides a foundation for material selection and the design of magnesium alloys.

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.