Magnesium Alloy Sheet Research Articles

Analysis on TIG Arc During Welding of Magnesium Alloy Sheet by a Combination of Spectral Diagnosing and Langmuir Probe Detection

Analysis on TIG Arc During Welding of Magnesium Alloy Sheet by a Combination of Spectral Diagnosing and Langmuir Probe Detection

Role of unusual double-peak texture in significantly enhancing cold rolling formability of AZ31 magnesium alloy sheet

Multi-pass cold rolling experiments were performed on AZ31 magnesium alloy sheet with unusual double-peak texture, where basal poles tilt about ±40° away from normal direction to rolling direction. This adopted sheet was fabricated by a novel technology of equal channel angular rolling and continuous bending process with subsequent annealing. Experimental results confirm that such an unusual double-peak texture contributes to a huge improvement of accumulated reduction up to 39.2%, which is over twice as much as that (18.3%) in sheet with strong basal texture. Optical microscopy and electron backscatter diffraction measurements demonstrate that the evolution of microstructure and texture in sheet with unusual double-peak texture is quite different from that in sheet with strong basal texture. Schmid factor (SF) analysis confirms that sheet with unusual double-peak texture possesses obviously large SF values for basal 〈a〉 slip {1012} and extension twin (ET) and remarkably small SF values for prismatic 〈a〉 slip and pyramidal 〈c+a〉 slip during cold rolling process. Therefore, basal 〈a〉 {1012} slip and {1012} ET will be activated more frequently in sheet with unusual double-peak texture to sustain plastic strain, leading to significant enhancement in cold rolling formability.

Investigation of Severe Plastic Deformation Effects on Magnesium RZ5 Alloy Sheets Using a Modified Multi-Pass Equal Channel Angular Pressing (ECAP) Technique.

The present study investigates the effects of multiple passes of equal channel angular pressing (ECAP) on magnesium alloy sheets with the assistance of an Inconel plunger along with a die setup having a channel angle of 120° and corner angle of 10° operating at a temperature of 200 °C followed by the required heat treatment processes. The microstructural analysis of the sheet samples at various stages of the multi-pass hot ECAP has shown evidence of ultrafine grain refinement (UFG) due to the occurrence of severe plastic deformation. X-ray diffraction analysis has also exhibited the presence of phases like MgZn and CeZn3 which is supposedly responsible for the enhancement of the mechanical properties. As a result, the room temperature tensile and compressive strengths have improved by 6.12% and 6.63%, respectively, after the second pass, and 11.56% and 15.64%, respectively, after the fourth pass of ECAP. Additionally, the hardness of the sheets has increased by 6.49% and 16.64% after the second and fourth pass of hot ECAP, respectively, mainly attributed to the drastic decrease in grain size from 164 μm to 12 μm within four ECAP passes, all these with a negligible change in ductility. This success in the thermomechanical processing of Mg-RZ5 alloy sheets using a die channel angle of 120° with a minimal number of passes of hot ECAP under a controlled equivalent strain, further opens doors for incorporating optimizations and/or additional aspects so as to achieve even better grain refinements, and consequently, mechanical strength improvements thereby catering to the industrial needs of aerospace and construction areas.

The improvement on mechanical anisotropy of AZ31 magnesium alloy sheets by multi cross-rolling process

The rolled AZ31 Mg alloy sheets were manufactured by unidirectional rolling and cross-rolling with two passes and five passes in this study. The improvement of multi cross-rolling on the anisotropy of mechanical properties, microstructure and texture of AZ31 Mg alloys was investigated by tensile fracture experiments, optical microscopy (OM) and electron backscatter diffraction (EBSD). The results indicate that the samples after rolling which were rotated by 90° showed weaker anisotropy than the samples rolled by 0° path. The ultimate tensile strength of the samples after 0° direction rolling increased from 236 MPa to 338 MPa on the transverse direction (TD) compared to as-rolled samples. The ultimate tensile strength of unidirectional rolling samples with two and five passes paralleled to TD is increased by 7% and 14% than that of cross-rolling samples. The enhanced mechanical properties are attributed to fine-grained strengthening, twin strengthening and dislocation strengthening. The {10−12} extension twin, {10−11} contraction twin and {10−12}-{10−11} double twin were investigated in the microstructure of samples by multi cross-rolling. All the samples showed the basal texture on the {0001} < 11–20 > . The basal texture of cross-rolling samples was apparently weakened for comparison to unidirectional rolling samples and the basal texture of five-pass cross-rolling samples was weaker than that of two passes. The improvement of anisotropy after cross-rolling can be attributed to grain refinement, the activation of non-basal slip and the weakening of basal texture.

Role of processing temperature on microstructure, mechanical properties and corrosion behavior of fine grained AZ31 magnesium alloy produced by groove pressing

AbstractAZ31 magnesium alloy sheets were processed at 250 °C and 300 °C by groove pressing, a severe plastic deformation technique to achieve grain refinement. The influence of processing temperature on the evolution of microstructure, mechanical properties and corrosion behavior was studied. Groove pressing significantly reduced the grain size of the alloy from 46 μm to 6.5 μm at 250 °C processing temperature. With the higher processing temperature (300 °C), grain growth (11.4 μm) was observed for the alloy. Number of twins appeared in the groove pressed samples. Higher hardness and tensile strength were measured for the groove pressed samples processed at 250 °C without significant loss in the ductility as reflected from the % of elongation due to the grain refinement. Corrosion performance of the samples assessed by potentiodynamic polarization studies indicated increased corrosion resistance for both of the grove pressed samples. However, sample at 300 °C exhibited better corrosion resistance compared with the sample processed at 250 °C. This can be understood by considering the effect of higher processing temperature on reducing the crystal imperfections which alters the corrosion behavior.

Influence of pulse energy on surface integrity of AZ31 magnesium alloy processed by femtosecond laser shock peening

Compared with traditional laser shock peening by nanosecond pulse laser, femtosecond laser shock peening (FLSP) exhibits superior flexibility and efficiency since it can be carried out directly in air without any ablative or confinement layers. In this work, FLSP was successfully performed on AZ31 magnesium alloy sheet. The influence of pulse energy on surface morphology and roughness, microstructure, surface residual stress and hardness was investigated in details. The results show that varying the laser pulse energy could effectively improve the surface integrity of the material. Regular dents are produced at the material surface with relatively low pulse energies, and the regular dent morphology disappears gradually with increasing pulse energy, suggesting an increased surface roughness. Surface microhardness and residual compressive stress are increased significantly after FLSP. The surface microhardness increases from the untreated 58.13 HV to the maximum value of about 69.58 HV at 37 μJ, by an increase of 19.7%. At 73 μJ, the residual compressive stress rises to a maximum value of approximately 59.6 MPa from an untreated 16.3 MPa. Moreover, the nano-hardness near the surface at the cross section is 1.68 GPa at 37 μJ, with an increase of 46% compared to the untreated 1.14 GPa. Particularly, twins and grain refinement layers are observed near the surface after FLSP, also indicated by the XRD analysis. The plastic deformation and grain refinement with low pulse energies contribute to the surface strengthening while the thermal effect and surface oxidation with increasing pulse energy may inhibit the enhancement of surface integrity.

Influence of tool pin shape and rotation speed for friction stir spot welding of AZ91 magnesium alloy sheets

Abstract Light weight design is believed one of the most effective ways to enhance performance, reduce fuel consumption and harmful gases for air and land vehicles. Hence, welding lightweight metals like magnesium alloys is very important. Friction stir spot welding joints of 2 mm thick AZ91 magnesium alloy sheets by overlapping two of them were performed utilizing two welding tools having conical and triangular pin at 800, 1200 and 1600 revolution per minute (rpm) tool rotational velocities for each tool to identify the pin shape and rotation speed impact on microstructure and mechanical features of the created joints. The stir zones of the joints contained smaller grains, therefore had higher hardness in comparison to AZ91 base metal, thermo-mechanically affected zone (TMAZ) and heat affected zone (HAZ). The lowest hardness values were found in HAZ of the welds. Hardness fell slightly with a rise in rotation speed for both tools because of more heat input. Strength of the joints manufactured applying the triangular pin tool was better because this pin mixed materials better, thus created joints with bigger welding area and greater hardness. The strongest weld was fabricated by applying triangular pin tool and 1600 rpm.

Mechanism of plasticity enhancement of AZ31B magnesium alloy sheet by accumulative alternating back extrusion

Accumulative alternating back extrusion was a potential fine-grain modification method. In this paper, it was an innovative attempt to develop high-performance magnesium alloy sheet by this process. Under the condition of 350 K, commercial AZ31 magnesium alloy was made into billet by accumulative alternating back extrusion, and then extruded into fine-grain magnesium alloy sheet. Through a systematic study of its microstructure and mechanical properties, the results showed that the initial state had an important influence on the evolution of the structure during extrusion. After accumulative alternating back extrusion to produce the billet, the grain size of the sheet obtained by extrusion was significantly refined, which was related to the accumulation of deformation and grain refinement during the alternating loading process. Grain refinement caused the proportion of dynamic recrystallization inside the sheet with 2 cycles of accumulative alternating back extrusion to drop to 27%. With the increase of extrusion cycles from 2 to 4, the high density of dislocations led to an increase in the proportion of dynamic recrystallization and finer grains. The texture changed from strong basal texture to weak bimodal texture. The results of uniaxial tensile test show that due to grain refinement and texture change, the yield strength was significantly reduced, and the plasticity was significantly improved. It was verified that accumulative alternating back extrusion was meaningful for subsequent processing, and it also provided scientific guidance for the development of fine-grained magnesium alloy sheet.

Comparison on crack propagation under tension at 150 °C of Mg-2Zn-1.5Mn alloy sheets with and without crack notch

Generally, edge crack of rolled magnesium alloy sheets initiates in the RD (rolling direction)-ND (normal direction) plane and then propagate in the RD-TD (transverse direction) plane. Hence, the Mg-2Zn-1.5Mn (ZM21) alloy sheets with and without crack notch were designed to carry out in-situ tensile experiments under 150 °C (the same temperature of rolling), with the aim to understand their crack propagation mechanism. The scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD) techniques were utilized to reveal microstructural evolution in real time at designated displacements. The results show that the prismatic slip, basal slip, and extension twining play synergistic role in coordinating strain during the tensile process in ZM21 alloy sheet at 150 °C. In both tensile samples with and without crack notch, localized strain is mainly concentrated at relatively fine grain area and the grain boundaries or triple junctions of the grains with large basal Schmid factor (SF) difference, which eventually leads to severe surface roughening and subsequent crack initiation. Compared with the sample without crack notch, the pre-cracked sample exhibits severer deformation at the crack tip due to strain concentration. Strain gradient distribution is observed at the crack tip region in the pre-cracked sample. The crack propagation path of the sample with pre-crack is identified and the underlying mechanism is also discussed.

Effect of Cryogenic Time on Microstructure and Properties of TRCed AZ31 Magnesium Alloy Sheets Rolled during Cryogenic Rolling

Rolling experiments of TRCed AZ31 magnesium alloy with different cryogenic treatment time were carried out to study the evolution mechanism of its microstructure and mechanical properties. The experimental results showed that with the increase in cryogenic time, the grain size of the sheets after cryogenic rolling was significantly refined, and the dislocation density and texture strength were greatly weakened. The combined effect led to a significant increase in the elongation and tensile strength of the sheet after cryogenic rolling. The tensile strength, elongation and average hardness of the sheet increased from 282.6 MPa, 8.2%, and 54.6 HV to 305.4 MPa, 16.3%, and 62.8 HV, respectively. Therefore, when the cryogenic treatment time was 60 s, the performance of the rolled sheet was the best. At the same time, the appearance of dimples after cryogenic rolling led to a change of the fracture mechanism, which was also the key to the improvement of the sheet elongation.

Joining magnesium and aluminum alloy sheets by a novel hole hemming process

The use of magnesium alloys represents a novel trend in the automotive industry, being used to manufacture high performance vehicle structures. These alloys possess the lowest density among all structural metals. However, the use of joining processes based on plastic deformation of magnesium alloys is restricted by the low formability of these materials at room temperature. In this research work, a novel joining process, called hole hemming, is developed for attaching magnesium AZ31 and aluminum AA6082-T4 alloy sheets in which only one of the sheets should be sufficiently ductile and there is no need for heating or using additional elements, such as rivets. Firstly, the fracture limits of the materials were characterized under different loading states. Then, the process for joining the mentioned material combination was designed with the support of finite element analysis and the critical regions prone to fracture and their loading paths were specified. In addition, the influence of process parameters on the mechanical interlock was investigated to determine process windows. A flexible tool was then developed and, for the first time, novel hole-hemmed joints were manufactured with different process parameters to thoroughly evaluate the performance of the designed process. Finally, single-lap joints were tested under shear loads. The results of this tests show that the novel hole hemming process can suitably join the magnesium and aluminum alloy sheets, with the hole-hemmed joints supporting a maximum load of 2.9 kN with a gradual failure mechanism of hole bearing. Thus, the hole hemming process is shown to be a viable technique for joining materials with very different formability.

Influence of In-Plane Simple Shear Strain on the Grain Orientation Regulation and Stretch Formability of Pre-twinned AZ31 Magnesium Alloy Sheet

Influence of In-Plane Simple Shear Strain on the Grain Orientation Regulation and Stretch Formability of Pre-twinned AZ31 Magnesium Alloy Sheet

Unveiling the Alloying-Processing-Microstructure Correlations in High-Formability Sheet Magnesium Alloys

Designing magnesium sheet alloys for room temperature (RT) forming is a challenge due to the limited deformation modes offered by the hexagonal close-packed crystal structure of magnesium. To overcome this challenge for lightweight applications, critical understanding of alloying-processing–microstructure relationship in magnesium alloys is needed. In this work, machine learning (ML) algorithms have been used to fundamentally understand the alloying-processing–microstructure correlations for RT formability in magnesium alloys. Three databases built from 135 data collected from the literature were trained using 10 commonly used machine learning models. The accuracy of the model is obviously improved with the increase in the number of features. The ML results were analyzed using advanced SHapley Additive exPlanations (SHAP) technique, and the formability descriptors are ranked as follows: (1) microstructure: texture intensity &gt; grain size; (2) annealing processing: time &gt; temperature; and (3) alloying elements: Ca &gt; Zn &gt; Al &gt; Mn &gt; Gd &gt; Ce &gt; Y &gt; Ag &gt; Zr &gt; Si &gt; Sc &gt; Li &gt; Cu &gt; Nd. Overall, the texture intensity, annealing time and alloying Ca are the most important factors which can be used as a guide for high-formability sheet magnesium alloy design.

Effect of two-step increased temperature thermal rolling on anisotropy and stretch formability of AZ31 magnesium alloy sheets

The effect of a two-step gradient thermal rolling process on the microstructure evolution and anisotropy as well as the stretch formability of AZ31 magnesium alloys was investigated. Step I was carried out at 300 °C with a small rolling reduction of 15% per pass, while the rolling temperature of Step II was 550 °C with per pass reduction of 40%. Finally, Mg alloy sheets with a thickness of 1 mm were achieved after total four rolling passes. The results indicate that shear bands are generated in rolled samples when the rolling direction is unchanged, while twinning lamellae and recrystallized grains emerge in samples when the rolling direction is changed in Step I. After Step II rolling, the size and amount of shear bands decrease, and grains are refined greatly owing to the enhanced activation of dynamic recrystallization. Besides, non-basal slips, especially prismatic 〈a〉 slips, are found to be promoted as well based on the in-grain misorientation axis (IGMA) analysis. Therefore, improved mechanical properties, reduced anisotropy, and the improvement of stretch formability of AZ31 Mg alloy sheets are achieved.

Texture and Tensile Properties of Three-Layered Titanium Clad–AZ31 Magnesium Alloy Sheet by Single-Pass Hot Rolling

Texture and Tensile Properties of Three-Layered Titanium Clad–AZ31 Magnesium Alloy Sheet by Single-Pass Hot Rolling

Effect of 90° route on microstructure of AZ31 magnesium alloy sheets by forging-bending repeated deformation

In this paper, a novel method of severe plastic deformation (SPD), i.e., forging-bending repeated deformation process, was proposed to prepare AZ31 magnesium alloy sheets. The effects of the new process on the equivalent strain, flow rate, microstructure, and hardness at different passes were investigated by finite element method (FEM), electron backscatter diffraction (EBSD) and Zwick/roll hardness tester. The results showed that the effective strain and flow velocity increased with the increase of the pass. Due to the transition path, the shear deformation was sufficient at each position and the uniformity was improved. After 4 deformation passes, the refined grain size was 5.02 µm on average. The dynamic recrystallization (DRX) mechanism in the first pass was discontinuous dynamic recrystallization (DDRX), and the interaction of twins- induced DRX and continuous dynamic recrystallization (CDRX) completed the microstructure evolution in the second pass. Meanwhile, {10−12} extension twins promoted the subsequent CDRX process by dividing coarse grains and changing grain orientation. In addition, slip-dominated pyramidal<c+a> slip was also committed to grain refinement, which can achieve high plasticity. Ultimately, the hardness of AZ31 magnesium alloy can reach 77.6HV after processing and deformation, and the grain size and high-density dislocation had significant effects on the distribution of hardness.

Experimental evaluation of cut quality and temperature field in fiber laser cutting of AZ31B magnesium alloy using response surface methodology

Fiber laser cutting of AZ31B magnesium alloy was studied to assess the effect of laser cutting process parameters on the resultant cutting temperature near the cut kerf and the resultant cut quality. To systematically analyze the effect of parameters on the temperature variation and cutting edge surface roughness during the cutting process of the AZ31B magnesium alloy, the Response Surface Methodology (RSM) was utilized to fit a quadratic polynomial model through the experiments. The influence of three main factors including speed of cutting, power of laser and nozzle distance on the major responses of temperature near the cut kerf, average surface roughness of the cutting edge and the cut kerf quality was then evaluated.Changes in the cutting speed had no serious impact on the quality of the cut kerf.Laser power levels from 800 to 1000 W were suitable for laser cutting of magnesium alloy sheets. The results showed thatvariations in the nozzle distance and laser emitted power had a remarkable effect on the temperature variation around the cut kerf width. Changing the nozzle distance and thereby creating different laser beam diameter had a more significant influence on the temperature variation rate (about 15 %), in comparison to the laser power. The nozzle distance had a huge effect on the cutting edge surface roughness due to the significant variation of laser beam energy density and beam diameter and hence, the cut kerf dimensional changes.The optimal cutting condition was obtained at the minimum roughness according to the investigated parameters levels, which included the cutting speed of 6 m/min, the power level of 1000 W and the nozzle distance of 0.8 mm. The SEM images from the top surface of the cut kerf implied the existence of oxidation in the magnesium alloy kerf edges.

Process Optimization of the Hot Stamping of AZ31 Magnesium Alloy Sheets Based on Response Surface Methodology.

Hot stamping is an important manufacturing process for sheet metal parts. However, it is easy to produce defects such as thinning and cracking in the drawing area during the stamping process. In this paper, the finite element solver ABAQUS/Explicit was used to establish the numerical model of the magnesium alloy hot-stamping process. The stamping speed (2~10 mm/s), the blank-holder force (3~7 kN), and the friction coefficient (0.12~0.18) were selected as the influencing factors. Taking the maximum thinning rate obtained through simulation as the optimization objective, the response surface methodology (RSM) was applied to optimize the influencing factors in sheet hot stamping at a forming temperature of 200 °C. The results showed that the maximum thinning rate of sheet metal was most influenced by the blank-holder force, and the interaction between the stamping speed and the blank-holder force/friction coefficient had a great influence on the maximum thinning rate. The optimal value of the maximum thinning rate of the hot-stamped sheet was 7.37%. Through the experimental verification for the hot-stamping process scheme, the maximum relative error between the simulation and the experimental results was 8.72%. This proves the accuracy of the established finite element model and the response surface model. This research provides a feasible optimization scheme for the analysis of the hot-stamping process of magnesium alloys.

Genetic effects of Mg-Zr master alloy in extruded thick sheets of ZK60 magnesium alloy

The genetic impact of Mg-Zr intermediate alloys is demonstrated in this article using ZK60 extrusion plates. The results demonstrate that the fine homogeneous distribution of submicron and nanoscale Zr particles is a critical contributor to the quality of the ZK60 alloy. It demonstrates that intermediate alloys have a genetic impact in the preparation of magnesium alloys.

Effect of rolling deformation on microstructure and mechanical properties of Mg–Y–Nd–Al alloy

In this paper, a low-cost and high-performance Mg–4Y–3Nd–1.5Al rolled magnesium rare earth alloy sheet was developed by a multi-pass rolling process. The effect of cumulative rolling deformation on the microstructure and mechanical properties of the alloy sheet was studied. It is found that with the increase of rolling passes, the proportion of dynamic recrystallisation grains increases, the grains are refined and the texture strength is weakened due to the combined effect of particle excitation nucleation mechanism and grain-boundary-induced nucleation mechanism. The results show that fine-grain strengthening and work hardening are the main reasons for the high strength of the alloy sheet. This experiment provides scientific guidance for developing fine-grained magnesium alloy sheets.