Extruded AZ31 Magnesium Alloy Research Articles

Modification of the Johnson-Cook relationship for AZ31 magnesium alloy at high strain rates

The establishment of Johnson-Cook (J-C) constitutive model is essential for the numerical analysis of high-speed impact. In this work, Dynamic compression experiments of extruded AZ31 magnesium alloy at various temperatures (298 K, 373 K, 473 K, and 573 K) and strain rates (700 s−1, 1000 s−1, and 1300 s−1) were studied using split Hopkinson pressure bar (SHPB). Based on the true stress-strain curves of the alloy collected by the experimental process, the strain term and temperature term of the Johnson-Cook model were modified, and the modified J-C model parameters with the temperature of 573 K and strain rate of 1300 s−1 were applied for the finite element simulation of the high strain rate deformation of AZ31 magnesium alloy. The results show that the modified J-C model is much better in agreement with the experimental results than that of the original one, and further the modified J-C model can accurately predict the compressive deformation behavior of AZ31 magnesium alloy during dynamic loading.

Microstructural Evolution and Mechanical Properties of Extruded AZ80 Magnesium Alloy during Room Temperature Multidirectional Forging Based on Twin Deformation Mode.

This study investigates the preparation of ultrahigh-strength AZ80 magnesium alloy bulks using room temperature multidirectional forging (MDF) at different strain rates. The focus is on elucidating the effects of multidirectional loading and strain rates on grain refinement and the subsequent impact on the mechanical properties of the AZ80 alloy. Unlike hot deformation, the alloy subjected to room temperature MDF exhibits a lamellar twinned structure with multi-scale interactions. The key to achieving effective room temperature MDF of the alloy lies in combining multidirectional loading with small forging strains per pass (6%). This approach not only maximizes the activation of twinning to accommodate deformation but ensures sufficient grain refinement. Microstructural analysis reveals that the evolution of the grain structure in the alloy during deformation results from the competition between {101¯2} twinning or twinning variant interactions and detwinning. Increasing the forging rate effectively activates more twin variants, and additional deformation passes significantly enhance twin interaction levels and dislocation density. Furthermore, at a higher strain rate, more pronounced dislocation accumulation facilitates the transformation of twin structures into high-angle grain boundaries, promoting texture dispersion and suppressing detwinning. The primary strengthening mechanisms in room temperature MDF samples are grain refinement and dislocation strengthening. While increased dislocation density raises yield strength, it reduces post-yield work hardening capacity. After two passes of MDF at a higher strain rate, the alloy achieves an optimal balance of strength and ductility, with a tensile strength of 462 MPa and an elongation of 5.1%, significantly outperforming hot-deformed magnesium alloys.

Flow softening and recrystallization accompanied flow in AZ61 magnesium alloy during thermomechanical processing

The present work deals with characterizing the recrystallization accompanied flow and high temperature softening behavior of an extruded AZ61 magnesium alloy. This was supported by conducting a set of hot compression tests at temperatures in the range of 250–450 °C under the strain rate ranging from 0.001 to 0.1s−1. The flow curves at all thermomechanical conditions indicated high fractional softening representing the domination of dynamic recrystallization mechanism. Through a new quantitative approach, “Arrhenius type model”, “modified Avrami equations” and Poliak and Jonas method were simultaneously employed to investigate the kinetic of dynamic recrystallization. It was revealed that the strain required for the same amount of recrystallization fraction increased with decreasing deformation temperature, and at a specified temperature, the required strain increases with increasing strain rate. Interestingly, an anomaly was found at 400 °C under the strain rate of 0.001s−1, where the recrystallization kinetic was faster than that of what was recorded at 450 °C. This anomaly was discussed relying on the nanoprecipitation of γ-phase at the prior boundaries and sub-boundaries which prohibited the grain boundary migration and also the rotation and coalescence of adjacent sub-grains.

Machine learning based prediction models for uniaxial ratchetting of extruded AZ31 magnesium alloy

The detrimental effect of ratchetting on the fatigue life of materials requires precise prediction models to guarantee the safety of engineering structures. This study focuses on predicting the uniaxial ratchetting of extruded AZ31 magnesium (Mg) alloy using machine learning (ML) based approaches. At first, the evolution and deformation mechanisms of ratchetting are summarized based on the existing experimental results of the Mg alloy. Subsequently, a semi-empirical prediction model, tailored for engineering applications, is developed to describe the evolution of ratchetting strain. Then, a pure data-driven ML based prediction model is proposed to overcome the shortcoming existed in the semi-empirical model and improve the prediction accuracy to the uniaxial ratchetting of the Mg alloy. Finally, a physics-informed ML based model, incorporating the physical information derived from the semi-empirical one, is proposed to further enhance its prediction accuracy and generalization ability. The comparison with correspondent experimental data demonstrates that the proposed physics-informed ML based model exhibits high prediction accuracy and generalization ability.

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.

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.

Effect of Pre-homogenization Treatment on Microstructure, Mechanical Properties, and Corrosion Resistance of Hot Extruded AZ61 Magnesium Alloy

Effect of Pre-homogenization Treatment on Microstructure, Mechanical Properties, and Corrosion Resistance of Hot Extruded AZ61 Magnesium Alloy

MICROSTRUCTURE EVOLUTION OF AZ31 MAGNESIUM ALLOY DURING TWIST CHANNEL ANGULAR PRESSING

Microstructure evolution of hot extruded AZ31 magnesium alloy during twist channel angular pressing was investigated. The grains were refined significantly after one to four passes at 200°C. Microstructure evolution after TCAP processing was investigated using optical microscopy, transmission electron microscopy and electron backscatter diffraction. The results show effect of TCAP process on the achieving the UFG structure with average grain size below 1 μm.

Effect of strain-induced grain boundary migration on microstructure and creep behavior of extruded AZ31 magnesium alloy prepared by pre-compression and annealing treatment

Effect of strain-induced grain boundary migration on microstructure and creep behavior of extruded AZ31 magnesium alloy prepared by pre-compression and annealing treatment

Multi-mechanism constitutive model for uniaxial ratchetting of extruded AZ31 magnesium alloy at room temperature

A multi-mechanism macroscopic phenomenological constitutive model is established to characterize the uniaxial ratchetting of extruded AZ31 magnesium (Mg) alloy at room temperature in the framework of small deformation. Because the uniaxial ratchetting of the alloy depends greatly on the strong basal texture and different deformation mechanisms (i.e., dislocation slipping, twinning and detwinning) and presents apparent tension-compression asymmetry, two separated yield functions and different hardening rules are used in the proposed model regarding to different deformation mechanisms. That is, the traditional von Mises yield criterion and a flow rule in power-law form are used for the plasticity contributed by dislocation slipping, while the Cazacu–Barlat–Plunkett (CPB) yield criterion extended with a back stress tensor and an internal variable f (i.e., twin volume fraction) is employed to express the plastic deformation induced by twinning/detwinning. In addition, the modified Armstrong-Frederick (A-F) kinematic hardening models are adopted to reflect the strain hardening features contributed by different plastic mechanisms, and the interaction among different plastic mechanisms is considered in the developed constitutive model. The reproduced uniaxial ratchetting of extruded AZ31 Mg alloy by the proposed multi-mechanism constitutive model is in a good agreement with the corresponding experimental results obtained at room temperature, which validates the reasonability and capability of the proposed model.

Microstructure and mechanical properties of AZ31 magnesium alloy prepared using wire arc additive manufacturing

AZ31 magnesium alloy structural parts were formed using the wire arc additive manufacturing technology (WAAM), and the microstructure and mechanical properties of the additive–substrate interface bonding zone and the additive zone were studied. Due to the repeated heating under the heat source during the additive manufacturing process, the longitudinal section of the additive zone had obvious non-uniform features. The grain size of the longitudinal section of the additive zone increased from 4.27 µm to 9.51 µm from the bottom zone to the top zone. The average fraction of "hard" grains in cross section was higher than that in longitudinal section, indicating that the cross section showed less plastic strain accumulation, resulting in lower plastic than the longitudinal section. The mechanical property anisotropy of the cross section was stronger because of its higher fiber texture strength. At the same time, the longitudinal section microhardness of the additive zone increased from 74.22 HV to 81.46 HV from the top zone to the bottom zone. The tensile strength of the WAAM AZ31 magnesium alloy in the vertical direction was 286.47 MPa, and its elongation rate was 15.89 %, which was considerably greater than the ultimate tensile strength of the cast and the extruded AZ31 magnesium alloy.

Effect of twinning and precipitation on low-cycle fatigue damage behaviour of extruded AZ80 magnesium alloy

In this paper, the fatigue behaviour and failure mechanisms of extruded AZ80 magnesium alloy samples were studied with different initial structures. The results show that the twinning-twinning behavior was inhibited to a certain extent by fine grain and precipitates, but the initiation of fatigue cracks was promoted. Studies of the fatigue life and fracture mechanism show that both residual twins and precipitated phases can cause fatigue crack initiation, but less fatigue damage is caused by the twin-induced cracks than by second phase-induced.

Phase field simulation on grain growth with particles located on grain boundaries

The grain size is a key characteristic to strongly affect the mechanical properties and performance, and the presence of additional phases plays an important role in affecting the microstructure evolution. In this work, a phase field model was adopted for immobile second-phase particles distributed at grain boundaries and analysed its pinning effect on polycrystalline grain growth. According to the size and distribution characteristics of second-phase particles in extruded AZ80 magnesium alloy, the effects of the particle morphology, particle size and volume fraction on the grain growth were investigated. The results showed that small-sized rod high-dispersion particles exhibit a stronger pinning effect on grain boundary migration. In addition, the generalised Zener relation of R lim = 2.49r sp/f sp −0.322 was obtained for the particles located at grain boundaries.

Damage evolution of extruded magnesium alloy from deformation twinning and dislocation slipping in uniaxial stress-controlled low cycle fatigue

The damage evolution of an extruded AZ31 magnesium alloy in uniaxial stress-controlled low cycle fatigue is investigated using a quasi-in-situ method. In the three studied samples, that is, slipping dominated (SD), twinning/detwinning/basal slipping (TDBS), and twinning/detwinning/slipping (TDS), the fractions of slip bands and/or twins keep increasing till a critical cyclic number, and are essentially unchanged in the subsequent cycles. Inter-granular micro-crack initiation is found to be favorable in the TDS and SD samples. While both the inter-granular and intra-granular micro-cracks are detected in the TDBS sample. Moreover, the non-Schmid behavior in the crack trans-granular propagation path is investigated.

Effect of axial preloading on mechanical behavior during the free-end torsion of an extruded AZ31 magnesium alloy

Effect of axial preloading on mechanical behavior during the free-end torsion of an extruded AZ31 magnesium alloy

Elasto-Plastic Fatigue Crack Growth Behavior of Extruded Mg Alloy with Deformation Anisotropy Due to Stress Ratio Fluctuation.

Fatigue crack growth (FCG) experiments were performed using a low-temperature extruded magnesium alloy AZ31 with texture. Under a constant maximum stress intensity factor (Kmax), the stress ratio R was changed from 0.1 to −1 during the fatigue crack growth process, and the FCG behavior before and after the R change was investigated. As a result, tensile twins were generated owing to the fatigue load on the compression side of R = −1, and the FCG velocity was accelerated. In addition, when the maximum compressive stress at R = −1 (|(σmin)R = −1|) exceeded the compressive yield strength of the material (σcy), the FCG velocity after R fluctuation greatly accelerated. On the other hand, under the condition |(σmin)R = −1| < σcy, the degree of acceleration of the FCG velocity due to R fluctuation was small. In either case, the degree of acceleration in the FCG increased as the Kmax value increased. The above FCG acceleration mechanism due to the R fluctuation was considered based on the observation of the deformation and twinning states of the fatigue crack tip, the fatigue crack closure behavior, and the cyclic stress–strain curve of the fatigue process. The FCG acceleration mechanism was as follows: First, the driving force of the FCG increased owing to the increase in crack opening displacement due to the generation of tensile twins. Second, the coalescence of the main crack and a plurality of microcracks were generated at the twin interface. The elasto-plastic FCG behavior after the stress ratio fluctuations is defined by the effective J-integral range ΔJeff.

An evolution of subsequent yield loci under proportional and non-proportional loading path of ‘as-received’ extruded AZ31 magnesium alloy: Experiments and CPFEM modeling

This work presents an experimental investigation of as-received extruded AZ31 magnesium alloy subjected to proportional and non-proportional loading paths at various finite levels of pre-strain. The measured subsequent yield loci evolutions in the σ11−3σ12 stress space, using a 10µε offset linearity definition of yield, with increasing plastic deformation are reported in this paper. Initial yield locus deviates substantially from a von-Mises yield loci. Subsequent yield loci under proportional loading show an usual nose in the loading direction and almost a flat shape in reverse loading direction. In addition, yield loci in all proportional loading paths (tension, free end torsion and combined tension-torsion) have significant kinematic and some isotropic hardening. Subsequent yield loci under non-proportional loading (tension after torsion and torsion after tension) show distortion in addition to significant kinematic and isotropic hardening, as well as, demonstrate a strong path-dependency. During these experiments with the increasing plastic strain, elastic moduli within each subsequent yield loci are also measured. These experimentally determined yield loci of as received AZ31 alloy are significantly different from the observed ones for aluminum alloys by Khan et al. (2009) and Iftikhar et al. (2021). However, these results are comparable to the ones reported recently by Iftikhar and Khan (2021) for annealed extruded AZ31 alloy. Numerical modeling using crystal plasticity models was carried out to study the origin of the distortion of the yield locus. The CP model is calibrated using the tensile and shear flow curves. Using the CP framework, initial and subsequent yield loci are predicted. CP predictions show good predictions. The CP simulations can capture the observed distortion and asymmetry in the yield loci. In addition, the CP simulations can give insight on the origin of the kinematic hardening, distortion and asymmetry. They show that these are correlated with activity of various slip systems and the amount of twinning occurring during the loading along different loading paths.

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.

Effect of Loading Direction on the Tensile Properties and Texture Evolution of AZ31 Magnesium Alloy

Samples were cut from an extruded AZ31 magnesium alloy bar for uniaxial tensile and EBSD characterization tests. The long axis and bar extrusion directions were 0° (T0 sample), 45° (T45 sample), and 90° (T90 sample). The effects of loading direction on the tensile behavior, microstructure, and texture evolution of the magnesium alloy were studied. Results show that the obvious mechanical anisotropy of tensile behavior is affected by the loading direction, and the T0 sample with a grain c-axis perpendicular to the extrusion direction has a strong basal texture and high flow stress and yield strength. The loading direction has a significant influence on the microstructure characteristics of different samples, especially the number of {10–12} tensile twins and {10–11} compression twins. Texture evolution results show that the loading direction and the effect of deformation mode on the deformation mechanism lead to variations in texture evolution: the basal slip and prismatic slip during the plastic deformation of the T0 specimen, the compression twin of the T45 specimen, and the tensile twin of the T90 specimen.

Effects of texture and stress sequence on twinning, detwinning and fatigue crack initiation in extruded magnesium alloy AZ31

Several types of cyclic stress were applied to specimens made of an extruded magnesium alloy, AZ31, to elucidate twinning, detwinning, and fatigue crack initiation mechanisms by electron backscattered diffraction analysis. In both the texture and the random orientation, twinning occurred under compressive stress exceeding the compressive yield strength. Detwinning occurred only in the texture upon the subsequent application of tensile stress less than the tensile yield strength of monotonic loading, whereas detwinning did not occur in the structure with random orientation. Under compression–compression fatigue test, successive twinning occurred, which changed the orientation of the basal plane. As a result, the random orientation of grains changed to the texture in which the normal of the basal plane was parallel to the loading direction. Cracks were formed along the boundary of grains with a high Schmid factor of the basal slip system and the misfit of grain on both sides was large. Near the crack initiation site, twin bands were observed; however, detwinning did not occur under the tensile stress after the cyclic compression loading.