Extruded AZ31 Magnesium Alloy Research Articles

The evolution of yield loci with finite plastic deformation along proportional and non-proportional loading paths in an annealed extruded AZ31 magnesium alloy

This investigation reports for the first time, the subsequent yield loci after finite plastic deformation based on 10με offset definition yield of an annealed extruded AZ31 magnesium alloy under proportional and non-proportional loading paths. The proportional loading paths comprise uniaxial tension, free end torsion, and combined tension-torsion radial paths. The tension loading followed by torsion, and torsion followed by tension are the non-proportional loading paths. Subsequent yield loci under proportional loading paths show a prominent nose in the loading direction and are almost flat in the unloading direction with evolution of significant isotropic hardening under tension and visible kinematic hardening under torsion loading path. Strong path-dependency is observed in subsequent yield loci under non-proportional loading directions along with hardening effects. All the yield loci are investigated in tension-torsion (σ₁₁-√3σ₁₂) stress space. The results are significantly different than observed for other metals, especially for aluminum alloys by Khan et al. (2009) and Iftikhar et al. (2021). Elastic moduli within each subsequent yield loci are also measured during these experiments with the increase in plastic strain. The observed small decreases in the elastic moduli with increasing plastic strains are very similar to the ones reported earlier (Iftikhar et al., 2021; Khan et al., 2009).

Effects of aging treatments on low-cycle fatigue behavior of extruded AZ80 for automobile wheel disks

The effect of precipitates on the strain-controlled fatigue of automobile wheel disks made of extruded AZ80 magnesium alloy was investigated via T5 and T6 peak aging. The age-hardening behavior, stress–strain response, fatigue fracture morphology, and fatigue crack path of the AZ80 wheel disks were characterized to determine their monotonic and cyclic deformation behaviors. The T5 and T6 peak-aging treatments significantly enhanced their hardness and monotonic strengths via precipitation hardening; as the precipitate amount increased, the twinning–detwinning behavior in the initial stage of cyclic deformation weakened accompany the strain hardening in the half-life cycle. According to the crack growth analysis, the propagation pattern was related to the coalescence of voids in the cyclic plastic zone. Compared with the extruded and T6-peak-aged counterparts, the highly dense lamellar phases in the T5 peak-aged sample suppressed the cyclic plastic deformation at the crack tip, deflecting the cracks and resulting in longer fatigue life at certain strain amplitudes. Thus, the T5 peak-aged sample exhibited excellent fatigue life at intermediate strain amplitudes (0.3%–0.8%).

Microstructure Evolution and Mechanical Properties of AZ31 Magnesium Alloy Sheets Prepared by Low-Speed Extrusion with Different Temperature

AZ31 magnesium alloy sheets were prepared by low-speed extrusion at different temperatures, i.e., 350 °C, 400 °C, and 450 °C. The microstructure evolution and mechanical properties of extruded AZ31 magnesium alloy sheets were studied. Results indicate that the low-speed extrusion obviously improved the microstructure of magnesium alloys. As the extrusion temperature decreased, the grain size for the produced AZ31 magnesium alloy sheets decreased, and the (0001) basal texture intensity of the extruded sheets increased. The yield strength and tensile strength of the extruded sheets greatly increased as the extrusion temperature decreased. The AZ31 magnesium alloy sheet prepared by low-speed extrusion at 350 °C exhibited the finest grain size and the best mechanical properties. The average grain size, yield strength, tensile strength, and elongation of the extruded sheet prepared by low-speed extrusion at 350 °C were ~2.7 μm, ~226 MPa, ~353 MPa, and ~16.7%, respectively. These properties indicate the excellent mechanical properties of the extruded sheets prepared by low-speed extrusion. The grain refinement effect and mechanical properties of the extruded sheets produced in this work were obviously superior to those of magnesium alloys prepared using traditional extrusion or rolling methods reported in other related studies.

Influence of Heat Treatment on Precipitation Behavior and Mechanical Properties of Extruded AZ80 Magnesium Alloy

By means of annular channel angular extrusion technology and solution treatment, the AZ80 supersaturated solid solution was prepared. The β-Mg17Al12 precipitate morphologies analysis along with its sizes and area fraction measurement was performed to investigate mechanical properties variation of alloy at various aging temperature. The results indicated that after solution treatment, the intergranular precipitate of as-extruded alloy was re-dissolved into the matrix, effectively decreasing the stress concentration, which was beneficial to the enhancement of elongation. At aging temperatures of 300 °C, Widmanstatten structure, lath-shaped precipitate, and intergranular precipitate were observed, while at 175–200 °C, cellular structure and oval-shaped particle were also identified. The morphology, area fraction, size of the precipitates, and PFZs (precipitate free zones) width worked together to affect the age-hardening behavior of the alloy. The strength and hardness of the peak-aged samples decreased with the increase in aging temperature, which is primarily attributed to the reduction in cellular structure area fraction and the corresponding increase in the interlamellar spacing, and the coarsening of the rhombus precipitate.

Interaction between texture evolution and dynamic recrystallization of extruded AZ80 magnesium alloy during hot deformation

The interaction between dynamic recrystallization (DRX) and texture evolution of AZ80 magnesium alloy during hot deformation was investigated by EBSD analysis. A series of compression experiments along extrusion (ED) and radius (RD) direction were carried out on the as-extruded AZ80 magnesium alloy with <101‾0>//ED fiber texture at 200–300 °C. The results show that there are a more homogeneous microstructure and a stronger softening trend on the true stress-strain curves in ED than in RD. Texture in ED tends to rotate towards the <0001>//ED basal texture and its total intensity weakens, while the <101‾0>//ED and <112‾0>//ED fiber texture in RD present a sharpening phenomenon. The compression in ED activates discontinuous dynamic recrystallization (DDRX) mechanism and forms dynamically recrystallized grains with random orientation, which is beneficial to optimize the texture and improve the formability of AZ80 magnesium alloy. The deformation in RD activates the continuous dynamic recrystallization (CDRX) mechanism and produces dynamically recrystallized grains following the orientation of parent grains, which results in the sharpening of the initial texture and is unfavorable for weakening the anisotropy of AZ80 magnesium alloy.

Mechanism of Secondary Deformation of Extruded AZ31 Magnesium Alloy by Viscoplastic Self‐Consistent Model

The viscoplastic self‐consistent (VPSC) model is used to establish a combination of different deformation mechanisms. By using this model, axial tension and compression tests of extruded AZ31 magnesium alloy at room temperature are simulated. The influence of secondary deformation mechanism (prismatic &lt;a&gt; slip, pyramidal &lt;c + a&gt; slip, and compression twin) on mechanical response and texture evolution is expounded. Increased activity of the prismatic &lt;a&gt; slip is conducive for the improvement of flow stress in mechanical response during axial tension and for the splitting of pole densities in the {0002} pole figure during axial compression. However, increased activity of the pyramidal &lt;c + a&gt; slip causes the basal texture to transfer to the extrusion direction in the {0002} pole figure during axial compression. The compression twinning has a negligible influence on the plastic deformation and mechanical response of AZ31 magnesium alloy during axial tension and compression. However, the compression twinning should be included in VPSC modeling to predict the texture evolution accurately.

Role of [formula omitted] twinning in the anisotropy and asymmetry of AZ31 magnesium alloy under high strain rate deformation

In order to investigate the role of {101‾2} extension twinning in anisotropy and asymmetry of highly textured magnesium alloy under high strain rate deformation, tensile and compression deformation were conducted by Split Hopkinson Tension and Pressure Bar under the strain rate of 1800s−1. With the help of theoretical calculated Schmid Factors (SFs), the dynamic tensile and compression behavior and deformation mechanism of extruded AZ31 magnesium alloy along extrusion direction (ED) and transverse direction (TD) were analyzed in the present paper. The results demonstrated that extruded AZ31 magnesium alloy shows obvious anisotropic and asymmetric behaviors under high strain rate deformation and the anisotropic and asymmetric behaviors are arisen from the different role of {101‾2} extension twinning. The Schmid Factor calculation results of six extension twinning variants revealed that the six variants have the same opportunity to activate under tensile loading along TD, while for compression along ED, only two variants have the opportunity of operating due to the highest SF among the six variants. When high strain rate tensile loading was applied along ED and compression loading along TD, {101‾2} extension twinning is not favored.

Fatigue crack initiation site and propagation paths in high-cycle fatigue of magnesium alloy AZ31

Plane bending fatigue tests were conducted under stress ratios of −1, −0.1, 0.1, and 0.5 at room temperature in a laboratory atmosphere to elucidate the fatigue crack initiation mechanism of an extruded AZ31 magnesium alloy. The fatigue life can be expressed as a unique function of the equivalent stress amplitude based on Smith–Watson–Topper theory independent of the stress ratio, and the dependence of the fatigue limit on the mean stress can be expressed by Morrow’s equation, both of which were proposed for conventional metals without twinning. In addition, the specimen surface was observed by optical microscopy and scanning electron microscopy (SEM), and the surface near the crack initiation site was analyzed by electron backscatter diffraction (EBSD) analysis to discuss the fatigue crack initiation mechanism. On the basis of the results of EBSD analysis, it is concluded that the existence of large grain with large Schmid factor of the basal slip system is essential for crack initiation, and the crack initiation mechanism is based on irreversible slipping and unrelated to twinning under the alternating stress condition (R = −1).

Effect of Precompression Deformation on the Strain-Controlled Low-Cycle Fatigue Behavior of Extruded AZ31 Magnesium Alloy

In this work, the effect of precompression along the extrusion direction on the strain-controlled low-cycle fatigue behavior of an extruded AZ31 magnesium alloy was investigated. After precompression deformation occurred, the tensile yield strength decreased, whereas the tensile yield strength and ultimate tensile strength increased gradually as precompression deformation increased. The shape of the stress–strain hysteresis of a specimen with 5% precompression deformation changed from asymmetrical to symmetrical compared with that of the as-extruded specimen. Hence, the whole process was likely dominated by twinning–detwinning behavior. Fractographic analysis revealed that the crack propagation region of the specimen with 5% precompression deformation was flatter than that of the as-extruded specimen because of the compressive mean stress and finer grains in the specimen with 5% precompression deformation. The fatigue lives of the as-extruded and precompression specimens were predicted by the Coffin–Manson model, the Ellyin energy model, the Smith–Watson–Topper model, the Fatemi–Socie model, and the Jiang model, respectively. The life predicted by the Ellyin energy model and the Jiang model was consistent with the experimental data.

AZ31 Magnesium Alloy Subjected to Severe Plastic Deformation at Different Temperatures: Microstructure and Hardness

.This paper is focuses on study of a hot extruded AZ31 magnesium alloy processed by severe plastic deformation method TCAP (Twist Channel Angular Extrusion) at different temperatures. In order to characterize processing temperatures and the resulting structure and properties, the specimens were processed by 4 passes at 250°C, 230°C and 200°C. Microstructure and mechanical characterization was performed by Vickers hardness testing and metallographic analysis on an optical microscope.

The effect of pre-twinning on the mechanical behavior of free-end torsion for an extruded AZ31 magnesium alloy

In this paper, the effect of pre-twinning on the mechanical behavior of free-end torsion (FET) for an extruded AZ31 Mg alloy was investigated via pre-compression along extruded direction with 1.5%, 3.5%, 5.5% and 6.5% plastic strain levels. After pre-compression, torsion was performed at room temperature. The yield strength was enhanced remarkably during FET test after 3.5% pre-compression. However, the change of yield strength is small during FET with pre-compression (PRC) greater than 3.5%. Refinement hardening induced by twinning contributes to the enhancement of yield strength for PRC 3.5 specimen. With pre-strain increasing, the change of yield strength is ascribed to dislocation hardening. The stage II and stage III of strain hardening were observed during pure torsion and FET test after 1.5% pre-compression. In contrast, the stage II is suppressed and the stage III only occurs during FETs after 3.5%, 5.5% and 6.5%. The pre-twinning favor the activation of prismatic slip under torsion, which enhances multiple slip and dynamic recovery. The transition of deformation mechanisms from basal slip to multiple slip leads to the change of strain hardening during FET after different pre-strain levels.

Biaxial Compressive Behavior and Tension-Compression Asymmetry on Plastic Deformation of Cast and Extruded AZ31 Magnesium Alloys

Biaxial Compressive Behavior and Tension-Compression Asymmetry on Plastic Deformation of Cast and Extruded AZ31 Magnesium Alloys

Transition from convex to concave of equal plastic work contours for wrought magnesium alloy under multi-axial loading

Due to non-proportional stress state in the forming process, an extruded AZ31 magnesium alloy is subjected to combined axial loading-torsion test. Pre-elastic axial tension and compression along extruded direction is performed firstly, then torsion loading with the axial stress unchanged, denoted as TT (Torsion after Tension) and TC (Torsion after Compression) loading is implemented respectively. The results show that the shape of the Equal Plastic Work Contour (EPWC) changes remarkably from convex to concave as plastic deformation increasing. Accordingly, the EPWC cannot act instantaneously as plastic potential which take place under proportional loading path. The microstructure of failure samples were observed to clarify the reason of transition from convex to concave. It is found that the twinning behavior is different during torsion after different axial stress which results from the variation of stress state during torsion and the restricted activity of twinning with c/a ratio decreasing. For pure torsion, the stress state facilitate the growth of twins. For pre-loading samples, the activity of twinning is restricted with the c/a ratio decreasing. However, the stress to activate twinning is satisfied under TC loading with the compressive stress component increasing with pre-elastic compression. The compressive stress component decrease with pre-elastic tension under TT loading. Therefore, twinning is activated under pure torsion and TC loading. Furthermore, the barrier effect of twin boundaries and dislocation-twin interaction strengthen basal slip and prismatic slip resulting in dislocation hardening. Texture hardening takes place by reorientation of grains induced by twinning. Both dislocation hardening and texture hardening lead to high strain hardening rate under pure torsion and TC loading. Therefore, the strain hardening rate and flow stress are much higher under pure torsion and TC loading than that of TT loading. Consequently, a transition from convex to concave of EPWC is obtained in large plastic strain.

Effects of free-end torsion on the microstructure evolution and fatigue properties in an extruded AZ31 rod

Pre-deformation influenced the microstructure of extruded magnesium alloys such that the mechanical properties and fatigue resistance of these alloys could be enhanced. In this study, free-end torsion was conducted to change the distribution of dislocation, extension twins and texture components in the extruded magnesium alloy AZ31 rod. Results showed that the extension twins at the center were induced not by shear strain but by the Swift effect. The compressive principal stress on the cylindrical surface greatly contributed to the formation of extension twins at the edge. The softening effect of de-twinning, which exceeded the impeditive effect of dislocations, significantly decreased the yield strength of magnesium alloy rods. Strain-controlled low-cycle-fatigue experiments were conducted on specimens subjected to different pre-torsion deformation conditions. The fatigue resistance of magnesium alloy rods was found to be enhanced by pre-torsion deformation, which was mainly related to the reduction of cyclic mean stress and cyclic stress amplitude, as well as to the slow strain hardening during the cyclic tensile-loading stage.

Effects of {10–12} Twins on Dynamic Torsional Properties of Extruded AZ31 Magnesium Alloy

Effects of initial twins on dynamic torsional properties of extruded AZ31 alloy were investigated by introducing {10–12} twins into it through precompression to 3 and 6% strains along the extrusion direction and performing torsional testing at a strain rate of 1.4 × 103 s−1 using a torsional Kolsky bar system. The as-extruded sample without twins showed higher dynamic torsional properties than the precompressed samples with many initial twins; the maximum shear strength and fracture shear strain decreased with increasing amount of initial twins. In the as-extruded sample, twinning occurred vigorously throughout the gage section of the tubular specimen during high-strain-rate torsional tests, resulting in heavily deformed morphology, many macrocracks, and rough fractured surfaces. The increased amount of initial twins suppressed the twinning behavior and localized the applied torsional deformation; this resulted in an almost unchanged sample shape, no secondary cracks, and a flat fracture plane, thereby deteriorating the dynamic torsional properties of the extruded alloy.

Electrochemical Corrosion of Magnesium Alloy AZ31 with Additive Lithium

AbstractThe purpose of performed tests was evaluation of resistance to electrochemical corrosion of extruded magnesium alloy AZ31 with additive of 4.5% Li. Corrosion tests were performed in 0.01-2.0 M NaCl solutions. Potentiodynamic tests enabled to register polarisation curves. With application of stereoscopic microscope Nikon SMZ745T and electron scanning microscope Hitachi S-4200, the surface of the alloy was observed after immersion tests performed in 1-6 days. Results of performed tests prove explicitly deterioration of corrosion properties of the alloy with the increase of molar concentration of NaCl solution. It can be seen that corrosion process is intensive and that intensity increases with the increase of solution concentration and extension of exposure time.

Deformation Mechanism and Hot Workability of Extruded Magnesium Alloy AZ31

Using the flow stress curves obtained by Gleeble thermo-mechanical testing, the processing map of extruded magnesium alloy AZ31 was established to analyze the hot workability. Stress exponent and activation energy were calculated to characterize the deformation mechanism. Then, the effects of hot deformation parameters on deformation mechanism, microstructure evolution and hot workability of AZ31 alloy were discussed. With increasing deformation temperature, the operation of non-basal slip systems and full development of dynamic recrystallization (DRX) contribute to effective improvement in hot workability of AZ31 alloy. The influences of strain rate and strain are complex. When temperature exceeds 350 °C, the deformation mechanism is slightly dependent of the strain rate or strain. The dominant mechanism is dislocation cross-slip, which favors DRX nucleation and grain growth and thus leads to good plasticity. At low temperature (below 350 °C), the deformation mechanism is sensitive to strain and strain rate. Both the dominant deformation mechanism and inadequate development of DRX deteriorate the ductility of AZ31 alloy. The flow instability mainly occurs in the vicinity of 250 °C and 1 s−1.

Grain Refinement of Extruded AZ31 Magnesium Alloy by Ecap Process

Grain Refinement of Extruded AZ31 Magnesium Alloy by Ecap Process

Hardness evolution of AZ80 magnesium alloy processed by HPT at different temperatures

Discs of an extruded AZ80 magnesium alloy were processed by high-pressure torsion (HPT) using 6.0GPa up to 10 turns at different temperatures (296K and 473K). The disc surfaces and cross-sectional planes were examined before and after processing using scanning electron microscopy (SEM) and Vickers microhardness (Hv). The microhardness results at the surface show differences in the strength of the material as a function of distance from the disc centres up to saturation, as well as a function of distance from the bottom to the surface in the cross-sectional plane. This study analyses the effect of processing temperature on the evolution of microhardness in the AZ80 magnesium alloy processed by high-pressure torsion.

Effects of Pre-Strain on the Evolution of Microstructure and Strain Hardening of Extruded Az31 Magnesium Alloy

Pre-compression 3% and pre-stretch 3% subsequent annealing at 200oC for 2h are conducted on AZ31 magnesium alloys, then inverse tensile and compressive deformation are carried out at room temperature, respectively. During inverse tension 3% deformation on 1st pre-compression samples, detwinning behavior happens; after 2nd pre-compression 3%, the volume fraction of {10-12} extension twins decreases comparing with 1st pre-compression. Due to the interaction of dislocation and induced twinning lamellas, strain hardening rate (θ) increases on 1st and 2nd pre-compression samples. {10-12} tensile twinning is restrained during inverse compressive deformation by pre-stretch process. Owing to the decreasing amount of twins, the texture strengthening in compressive deformation weakens. So the slop of stage III in strain hardening rate sustaining reduces after 1st pre-stretch 3% and 2nd pre-stretch 3% deformation during inverse compression deformation.