AZ31 Magnesium Alloy Research Articles

Effect of rolling reduction on microstructure and tension-compression yield asymmetry of rolled AZ31 magnesium sheet

Magnesium (Mg) alloys have been receiving significant applications in automotive and aerospace industries owing to its high strength-to-weight ratios. Approximately 30 % (by weight) of material used in automobiles are in the form of sheet metal. Therefore, in the present work AZ31 magnesium (Mg) alloy was hot rolled with different reduction ratios to produce Mg sheet. The results revealed that employing a 40 % reduction per pass led to a remarkable 92 % reduction in thickness, outperforming the 82 % reduction achieved with a 20 % reduction per pass, along with fine grain of 8 μm. Investigation has been conducted on the relationship between grain size and its impact on the tension-compression yield asymmetry in Mg sheet. This investigation unveiled that the suppression of {101‾2} extension twinning mode of deformation due to the back stress imposed by the simultaneous action of grain boundaries and twin overlap, effectively minimizing the asymmetry from 2.11 (as received AZ31 alloy) to 1.13 (5th pass rolling sheet). The study extensively explored the underlying mechanisms governing the yield asymmetry behavior of AZ31 Mg sheets. These mechanisms included strain hardening tendencies, Schmid Factor, and KAM (Kernel Average Misorientation) assessment, all of which were interconnected with microstructural attributes.

Room and cryogenic deformation behavior of AZ61 and AZ61-xCaO (x = 0.5, 1 wt.%) alloy

This study investigates the influence of CaO (0.5, 1 (wt.%)) alloying on the microstructural evolution, texture development and deformation behavior of AZ61 magnesium alloy. The uniaxial tension tests at room (RT) and cryogenic (CT, -150 °C) temperature were performed to investigate the twinability and dislocation behavior and its consequent effect on flow stress, ductility and strain hardening rate. The results showed that the AZ61-1CaO exhibited superior strength/ductility synergy at RT with a yield strength (YS) of 223 MPa and a ductility of 23% as compared to AZ61 (178 MPa, 18.5%) and AZ61-0.5CaO (198 MPa, 21%). Similar trend was witnessed for all the samples during CT deformation, where increase in the YS and decrease in ductility were observed. The Mtex tools based in-grain misorientation axis (IGMA) analysis of RT deformed samples revealed the higher activities of prismatic <a> slip in AZ61-CaO, which led to superior ductility. Moreover, subsequent EBSD analysis of CT deformed samples showed the increased fraction of fine {10-12} tension twins and nucleation of multiple {10-12} twin variants caused by higher local stress concentration at the grain boundaries, which imposed the strengthening by twin-twin interaction. Lastly, the detailed investigations on strengthening contributors showed that the dislocation strengthening has the highest contribution towards strength in all samples.

Mechanism of texture evolution propelled by recrystallization behavior of interactively alternating forward extruded AZ31 magnesium alloy under pre-upsetting deformation

Pre-upsetting deformation is an effective way to optimize the microstructure of plastic forming components and achieve deep modification. In this paper, the pre-upsetting deformation of AZ31 Mg alloy billet was carried out before alternating forward extrusion, and the effect of pre-upsetting deformation temperature on the recrystallization behavior and texture evolution of AZ31 Mg alloy formed by alternating forward extrusion was analyzed. The results showed that the strains generated by the pre-upsetting deformation at different temperatures all leaded to a high dynamic recrystallization (DRX) driving force. This results in a high percentage of recrystallized grains in all pre-upsetting alternating forward extrusion (UAFE) formations. The highest percentage of recrystallized grains 94.5% was observed in U2AFE (pre-upsetting deformation at 623 K). The behavior of DRX has a significant impact on both the distribution and strength of texture. In the case of U2AFE, the maximum basal texture strength is 8.65. This is due to the maximum pole density of the deformed texture, which is composed of non-recrystallized grains and is as high as 9.25. In contrast, the maximum pole density of the recrystallized texture, which is composed of recrystallized grains, is only 8.09. Therefore, non-recrystallized grains play a crucial role in the formation of texture in UAFE. This study provides scientific guidance and technical support for the research of high-performance Mg alloy alternating forward extrusion molding technology.

Transverse difference of activation slip/twin system in wide AZ31 alloy plate during its rolling

The macroscopic finite element method (FEM) and the crystal plasticity finite element method (CPFEM) were combined to study the transverse difference of activation slip/twin system in wide AZ31 magnesium alloy plates during rolling. The macro-deformation and micro-texture evolution along the transverse direction of the plate during rolling were analyzed experimentally. The microscopic CPFEM was developed on the basis of the thermo-force coupling behavior during plate rolling obtained from macroscopic FEM. The CPFEM parameters were fitted by uniaxial compression experiments. This combination of two scale simulations accurately predicted the texture evolution during the rolling process and had been experimentally validated. Further examination of the deformation mechanism reveals that the transverse spread action of the plate is stronger at the edge region compared to center, and this transverse spread action has a more significant impact on the activation of the {10 1‾ 2} tension twin. The comparison of the activation and extension of pyramidal <a> slip in granular and plate-like grains reveals that plate-like grains are more prone to generate slip bands through the grain, leading to cracking of the grain along the slip activation band and further formation of sub-grains.

Experimental observations on the nonproportional multiaxial ratchetting of cast AZ91 magnesium alloy at room temperature

Experimental observations on the nonproportional multiaxial ratchetting of cast AZ91 magnesium alloy at room temperature

Dynamic strength differential and Bauschinger effects in an extruded AZ80 magnesium alloy

Quasi-static and high-rate tension and compression properties of an extruded AZ80 Mg alloy rod were investigated at loading rates of 0.001 and 500 s−1. Acquired stress – strain results show that tension and compression plastic deformations of AZ80 rod are asymmetric, and such strength differential effect is dependent of strain rate and loading orientation. Strength differential effect is weakened at 500 s−1 when the sample was loaded along the extrusion direction. Crystal plasticity simulations on the basis of the visco-plastic self-consistent method were performed. Numerical results indicate that the rate and orientation dependency of strength differential effect in AZ80 alloy is related to {101‾2} extension twinning. High-rate tests for pretension, unloading and reverse compression were realized to investigate the dynamic Bauschinger effect. Experimental results show that Bauschinger effect of AZ80 alloy is anisotropic and sensitive to the strain rate. A Bauschinger effect parameter considering strength differential effect was proposed, and it was found that the Bauchinger effect in the extrusion direction is reduced significantly at 500 s−1.

Effect of liquid nitrogen assisted milling on AZ91 magnesium alloy

The objective of the present work is to study the effect of liquid nitrogen (LN2) cryogenic on the performance of face milling for producing quality surface in AZ91 magnesium alloy. Machining AZ91 alloy has been a challenging domain due to the risk of ignition or spark during machining, which affects surface finish. In this study, face milling is carried using uncoated carbide inserts in cryogenic condition, and the performance is compared with dry condition based on the surface integrity (SI) characteristics. The findings of this study reveal that use of LN2 results in enhanced surface integrity. Observations showed no harm to alloy microstructure in both conditions, with no alterations to grain integrity in the near machined area. Cryogenic machining resulted in reduction in machining temperature ranging from 146.7 °C to 178.5 °C, when compared to dry condition temperature ranging from 219.4 °C to 251.2 °C. Cryogenic machining considerably generated smoother (Ra = 0.0606 μm) and harder (HV = 116.5) surfaces, and also resulted in compressive residual stresses. This study concludes that cryogenic-assisted milling is an excellent alternative for the production of superior-quality surface in AZ91 alloy.

The production of $B_{4}C$ reinforced metal matrix composite from waste $AZ91$ magnesium alloy using the ball milling method

In this study, the Mg/$B_4$C composite reinforced with boron carbide particles was produced by mechanical milling method using waste AZ91 magnesium alloy chips. The mechanical and tribological properties of the produced composites were investigated through hardness and wear tests. A mixture of AZ91 magnesium alloy chips, aluminum, and $B_4$C powders was milled at a rotation speed of 300 rpm with a ball-to-powder ratio of 20:1 for 3 hours. The milled powders were first cold pressed and then sintered at 550 °C for 3 hours. In density measurement, it was observed that the sample reinforced with B4C exhibited an increase in density. In X-ray diffraction analysis, peaks corresponding to Mg, $Mg_{17}Al_{12}$, and MgO were detected, while the $B_4$C phase could not be identified. On the other hand, $B_4$C particles in the microstructure were revealed in the energy dispersive X-ray spectroscopy analysis. Scanning electron microscope images revealed that the Mg/$B_4$C composite had lower porosity, consistent with density measurements. It was found that the hardness and wear resistance of the Mg/B4C composite were higher than those of the Mg alloy, which can be attributed to the presence of homogenously distributed hard B4C particles within the microstructure.

A Study of {10-12} Twinning Activity Associated with Stress State in Mg-3Al-1Zn Alloy during Compression

An eight-sided prism sample, obtained from a hot-rolled AZ31 magnesium alloy sheet, was compressed at room temperature along the transverse direction to investigate the influence of local strain on twinning behavior using electron backscatter diffraction (EBSD) measurements, hardness distribution, and metallographic observations. The octagonal surface of the sample was divided into distinct regions based on hardness distribution and metallographic observations. Combined analysis of the Schmid factor (SF) and the strain compatibility factor (m’) was employed to study twin variant selection. Basal on SF ratio distribution, the Schmid factor criterion, can predict over 75% of observed twin variants in regions A and D (normal stress samples). In contrast, 64% of twin variant selection behavior in region C (shear stress sample) can be effectively explained using a pure shear model. Twin variants with high strain compatibility factors may prefer activation to reduce stress concentration. The strain compatibility factor is more appropriate than the Schmid factor for analyzing the effect of local strain on the selection behavior of twin variants.

Electrochemical investigation of electrophoretically deposited graphene-oxide coating on AZ31 alloy prepared using in-house synthesized few-layer graphene-oxide nanosheets

Magnesium and its alloys possess low density and superior specific strength making it a potential structural metal to be used in different engineering fields. However, its proneness to corrosion limits its applications. In this novel study, an eco-friendly graphene-oxide coating was prepared on AZ31 magnesium alloy via electrophoretic deposition to enhance its anti-corrosion properties. Scanning electron microscopy coupled with energy dispersive spectroscopy, atomic force microscopy, and scratch test were adopted to investigate surface morphology, roughness, chemical composition, and adherence of the coating. The corrosion behaviour of graphene-oxide coated alloy was studied using potentio-dynamic polarization and electrochemical impedance spectroscopy tests in 3.5 wt% NaCl and Borate Buffer solutions. The obtained results demonstrate that the coating developed on AZ31 alloy is smooth and adherent with the hardness of the as-deposited coating measuring as high as 6.0 GPa. In addition, the electrochemical corrosion behaviour studies revealed that the coating significantly increased the corrosion potential (Ecorr) of the alloy towards more noble values (−0.65 V < Ecorr < −0.35 V), with the coated alloys possessing a charge transfer resistance nearly two orders of magnitude greater than their non-coated counterparts. Consequently, the corrosion rate of the coated alloy decreased substantially, indicating that the coating exhibits exceptional corrosion resistance (0.045–0.09 mm/a in 3.5 wt% NaCl and 0.002–0.006 mm/a in Borate Buffer). These findings challenge the conventional beliefs that graphene exhibits strong cathodic behaviour towards anodic materials such as AZ31 alloy. Thus, the outcomes not only have the potential to revolutionize the advancement of graphene-oxide coatings for corrosion resistance but could also possibly expand AZ31 alloy’s applications in the aerospace and automotive sectors.

Mechanical responses and deformation mechanisms in the AZ31 magnesium alloy during cyclic bending

Cyclic loading behavior, such as cyclic bending, is unavoidably involved in various forming processes and the service of end products. Understanding the mechanical behavior of magnesium (Mg) alloys under cyclic bending is essential for promoting their application. Despite existing research, the microscopic mechanisms at play during cyclic bending, specifically the slip and twinning-de-twinning (TDT), warrant further exploration, which is the innovative focus of our study. To address this need, cyclic bending tests were performed on an extruded AZ31 Mg plate with the in-situ digital-image-correlation (DIC) technology. And the texture evolution was determined through electro backscattered diffraction (EBSD) measurements. Concurrently, the crystal-plasticity-based bending-specific approach, EVPSC-BEND, incorporating the TDT scheme, is utilized to interpret the mechanisms involved in cyclic bending. The impact at the macroscopic level is manifested in asymmetric cyclic moment-curvature curves, stress-strain distribution, and shifting of the neutral layer. The developed textures at different regions of the beam and the twin volume fraction distribution further directly illustrate twinning-de-twinning behaviors. Particularly, the upper and lower halves of the beam experience very distinct cyclic behaviors simultaneously. The upper half experiences a twinning, detwinning, and twinning cycle, while the lower half experiences a twin-free, twinning, and detwinning cycle. Additionally, through modeling the cyclic bending with different initial textures, the strong texture dependence has been revealed. The behaviors of magnesium alloy beam under cyclic bending discovered in this work can shed light on the application of Mg alloys, such as forming processes and service of end product.

Shot peening of AZ31 magnesium alloy: role of surface microstructure and iron diffusion on corrosion behaviour

ABSTRACT In the present work, surface grain refined AZ31 magnesium (Mg) alloy was produced by shot peening (SP). X-ray diffraction analysis demonstrated iron diffusion into the surface of AZ31 Mg alloy during SP. Higher hardness, increased surface energy and decreased corrosion resistance were observed for the shot-peened surface due to nanostructured grains resulted from SP. From the immersion studies in a simulated physiological solution carried out for 3 days, higher level of biomineralization was observed for the shot peened AZ31 compared with the base alloy that dominated the adverse effect of iron diffusion in resisting the biocorrosion. The results suggest that the nano-structuring of AZ31 Mg alloy surface helps to enhance the biomineralization to control the degradation. However, the selection of processing medium is crucial to eliminate the effect of chemical composition change during the process in tailoring the corrosion behaviour of AZ31 Mg alloy for biomedical implant applications.

Enhanced mechanical properties of thermo-mechanically affected zone of friction-stir welded AZ61 magnesium alloy joint

Friction-stir welded (FSW) magnesium alloy joints frequently fracture at thermo-mechanically affected zone (TMAZ), and the joints exhibit unsatisfactory welding efficiency and ductility. The TMAZ is considered as the weakest region of the entire joint. Enhance the mechanical properties of TMAZ can improve the performance of the welded joint. In this work, subsequent aging treatment and pre-strain of 3% along the weld seam were conducted on the FSW AZ61 magnesium alloy joint. The microstructure of the TMAZ is characterized by abundant nanoscale second phase particles and {10–12} twins. The reduced basal texture intensity decreased the anisotropy of plastic deformation. The welded joint showed a good synergic of welding efficiency (96%) and ductility (20%). The enhanced strength is attributed to the blocking effect of nanoscale particles and grain/twin boundaries to dislocation movement. The increasing of twin boundaries is the main reason for the improvement of work hardening ability and ductility during tensile deformation. This work demonstrated that introducing {10–12} twins and nanoscale particles into TMAZ is an effective way to improve the balance of strength and ductility of the welded joint due to the synergistic effect of multiple strengthening and toughening mechanisms.

Microstructural Evolution and Mechanical Properties of AZ31 Magnesium Alloy Processed through Constrained Groove Pressing at Different Deformations and Temperatures

Microstructural Evolution and Mechanical Properties of AZ31 Magnesium Alloy Processed through Constrained Groove Pressing at Different Deformations and Temperatures

A novel forming process of AZ31 magnesium alloy square tube based on numerical simulations and experiments

A novel forming process of AZ31 magnesium alloy square tube based on numerical simulations and experiments

Effect of Zinc and Severe Plastic Deformation on Mechanical Properties of AZ61 Magnesium Alloy.

This study investigates the effects of zinc (4 wt.%) and severe plastic deformation on the mechanical properties of AZ61 magnesium alloy through the stir-casting process. Severe plastic deformation (Equal Channel Angular Pressing (ECAP)) has been performed followed by T4 heat treatment. The microstructural examinations revealed that the addition of 4 wt.% Zn enhances the uniform distribution of β-phase, contributing to a more uniformly corroded surface in corrosive environments. Additionally, dynamic recrystallization (DRX) significantly reduces the grain size of as-cast alloys after undergoing ECAP. The attained mechanical properties demonstrate that after a single ECAP pass, AZ61 + 4 wt.% Zn alloy exhibits the highest yield strength (YS), ultimate compression strength (UCS), and hardness. This research highlights the promising potential of AZ61 + 4 wt.% Zn alloy for enhanced mechanical and corrosion-resistant properties, offering valuable insights for applications in diverse engineering fields.

Fe/Cu doped black ceramic coating on magnesium alloy by plasma electrolytic oxidation method based on first principles

The absorption of visible light by a solid material can correspond to its color. If all visible light is absorbed, the material is black, and the band width of the material defines the wave limit of visible light absorption. Based on this, the transition metal elements Fe and Cu were chosen to dope MgO, and the transition metal elements Fe or Cu were substituted to dope MgO using first-principles simulation. The doped elements' 3d and 4 s levels were introduced to shift the locations of MgO's valence and conduction bands, respectively, lowering the band gap width of MgO. The MgO ceramic coating may respond to light wave wavelength redshifting to 780 nm and entirely absorb visible light; The black MgO ceramic coating was prepared on the surface of AZ31 magnesium alloy utilizing Fe salt and Cu salt as plasma electrolytic oxidation (PEO) electrolyte additions, and the visible light absorption rates were 94.2 % and 94.1 %, respectively. The test findings show that the band gap of the MgO ceramic coating has been lowered from 4.97 eV to 1.58 eV and 1.60 eV, respectively, which is the primary reason for the achievement of strong absorption in all visible light bands. The first principle calculation of the influence of doping elements on the band gap of MgO ceramic coating can serve as a theoretical guidance for selecting coloring elements for the fabrication of black ceramic coating.

Surface modification of AZ61 Magnesium Alloy with Stelcar Alloy Powder Using Laser Cladding Technique

Objective: To examine the tribological and mechanical characteristics of the AZ61 alloy reinforced with Stelcar alloy powder by surface modification through laser cladding. Methods: Surface modification was done by using a laser cladding machine, where the input parameters including Scanning Speed (SS), Laser Power (LP) and Powder Feed Rate (PFR) were adjusted. Experimental design followed a L9 Taguchi approach, and optimization of input parameters for the surface modified AZ61 alloy reinforced with Stelcar alloy particles was achieved using Grey Relational Analysis (GRA). Output responses, namely wear volume and micro hardness were measured to assess the effectiveness of the optimization process. Findings: From the results obtained through the experiments, powder feed rate contributes to 82.81% of the variability in wear volume, whereas the laser power mostly impacts micro hardness; influencing it by 89.46% confirmed with ANOVA. In order to determine the optimal processing parameters among various objectives, this research applies the grey relational method. The results showed that the wear volume and micro hardness of the composite were significantly affected by the Stelcar reinforcement. Employing Grey relational analysis combined with several optimization objectives into a transparent method, resulting in a clad material with the lower wear volume and higher micro hardness. The optimized processing parameters predicted grey relational grades with an error rate of 1.39% and a significant contribution of 63.60% from laser power. This study confirmed that multi-objective optimization could enhance laser-cladded surface mechanical characteristics and laid out the theoretical foundation for this approach. Novelty: This study introduces an innovative approach to surface modification by employing the laser cladding technique to reinforce Stelcar alloy particles, thereby creating a dense coating on the substrate. Keywords: Laser Cladding, AZ61 magnesium alloy, Stelcar alloy, Coating, Optimization

The importance of ammonium and potassium ions under hydrothermal preparation conditions on the structure and corrosion properties of CaP coatings

CaP coatings were hydrothermally deposited on the AZ31 magnesium alloy in rection mixture containing ammonium or potassium ions. CaP coatings were deposited on AZ31 alloy in reaction mixture at pH 5 and 7 with and without EDTA chelating agent. It was found that the ammonium ions present have a negative effect on the quality of the CaP coating deposited from mixture at pH 7 and their presence at neutral environment results in the formation of structural defects in the coatings. At the same time, the presence of ammonium ions suppresses hydrolysis and crystallization of OCP and HAp. However, pH and the presence of EDTA have a more pronounced effect on the structure and phase composition. The coatings deposited in the reaction mixture, containing potassium-based precursors and EDTA, at pH 7 showed the best thermal stability due to the majority of HAp phase. The uniform CaP coating deposited in the reaction mixture containing EDTA and K+ ions at pH 7 also achieved the best corrosion properties due to the absence of structural defects and dense structure.

Enhancing fatigue performance of AZ31 magnesium alloy components fabricated by cold metal transfer-based wire arc directed energy deposition through LPB

Cold Metal Transfer-Based Wire Arc Directed Energy Deposition (CMT-WA-DED) presents a promising avenue for the rapid fabrication of components crucial to automotive, shipbuilding, and aerospace industries. However, the susceptibility to fatigue of CMT-WA-DED-produced AZ31 Mg alloy components has impeded their widespread adoption for critical load-bearing applications. In this study, a comprehensive investigation into the fatigue behaviour of WA-DED-fabricated AZ31 Mg alloy has been carried out and compared to commercially available wrought AZ31 alloy. Our findings indicate that the as-deposited parts exhibit a lower fatigue life than wrought Mg alloy, primarily due to poor surface finish, tensile residual stress, porosity, and coarse grain microstructure inherent in the WA-DED process. Low Plasticity Burnishing (LPB) treatment is applied to mitigate these issues, which induce significant plastic deformation on the surface. This treatment resulted in a remarkable improvement of fatigue life by 42%, accompanied by a reduction in surface roughness, grain refinement and enhancement of compressive residual stress levels. Furthermore, during cyclic deformation, WA-DED specimens exhibited higher plasticity and dislocation density compared to both wrought and WA-DED + LPB specimens. A higher fraction of Low Angle Grain Boundaries (LAGBs) in WA-DED specimens contributed to multiple crack initiation sites and convoluted crack paths, ultimately leading to premature failure. In contrast, wrought and WA-DED + LPB specimens displayed a higher percentage of High Angle Grain Boundaries (HAGBs), which hindered dislocation movement and resulted in fewer crack initiation sites and less complex crack paths, thereby extending fatigue life. These findings underscore the effectiveness of LPB as a post-processing technique to enhance the fatigue performance of WA-DED-fabricated AZ31 Mg alloy components. Our study highlights the importance of LPB surface treatment on AZ31 Mg components produced by CMT-WA-DED to remove surface defects, enabling their widespread use in load-bearing applications.