Magnesium Alloy Sheet Research Articles

Unveiling the formation of gradient microstructure in the magnesium alloy sheet fabricated via turned-bearing extrusion

On certain occasions, such as bending, a sheet with gradient microstructure may present higher formability compared to one with uniform microstructure. In this study, the formation of gradient microstructure in AZ31 alloy sheets extruded by the asymmetric die is comprehensively investigated. The results exhibit the microstructure evolution undergoes three stages, namely the initial dynamic recrystallization (DRX), abnormal grain growth (AGG), and the secondary DRX. After the initial DRX, the microstructure is fine and uniform, and the transverse direction (TD) preferred texture is formed due to the initiation of non-basal slip. Owing to the high extrusion temperature, AGG occurs after the initial DRX. The grains with basal texture are engulfed by the grains with TD-preferred texture. During the AGG, the grain size is coarsened from 11.4 μm to 382.1 μm. As the material flows through the die bearing, the secondary DRX occurs near the corner of the die. Ascribed to the gradient strain near the bearing, the grains near the bottom surface of the sheet are refined again, while those near the other side inherit the large sizes from grown grains. Ultimately, the extruded sheet exhibits gradient microstructure along the thickness direction, i.e. normal direction (ND). The gradient-distributed plastic strain and strain rate are the main causes of gradient microstructure.

Influence of cryogenic treatment time on the mechanical properties of AZ31 magnesium alloy sheets after cross-rolling

To investigate the influence of cryogenic treatment time on the mechanical properties and the microstructure of the AZ31 Mg alloy sheets, the different times of cryogenic treatment after two-pass cross-rolling were carried out at air-cooling, 1 hour, 3 hours and 6 hours. The consequences of the tensile experiment illustrated that the cross-rolling Mg alloy with 1-hour cryogenic treatment showed the highest ultimate tensile strength (343 MPa), which was 9.6%, 9.6% and 11.7% higher than air-cooling, 3-hour cryogenic and 6-hour cryogenic samples. The primary reasons for this include fine-grained strengthening, twin strengthening, low-angle grain boundaries (LAGBs) strengthening, dislocation strengthening and precipitation strengthening. The internal grain of the magnesium alloy sheet after 1 hour of cryogenic treatment was refined to 5.2 μm. The {10−11} contraction twin, {10−12} extension twin and {10−12}-{10−11} double twin were surveyed according to the electron backscatter diffraction (EBSD) results. On the <11–20> axis, all the four samples exhibited the {0001} basal texture. And the sample of 1-hour cryogenic treatment exhibited the highest basal texture intensity. According to the micro-structure observation, high-density dislocation and several precipitates were illustrated in the sample of 1-hour cryogenic treatment.

Microstructure evolution and deformation behaviors of AZ31 Mg alloy sheets processed by repeated bending−flattening deformation with different die angles

AZ31 magnesium alloy sheets were fabricated by repeated bending−flattening deformation (RBFD) using dies of various angles. The microstructure evolution and deformation behaviors of the AZ31 Mg alloy during RBFD were investigated by FEM, OM, EBSD and hardness tester. The results suggest that the 150°/150° die exhibits the superior performance across all three groups. With an increase in passes, the effective strain of the alloy is significantly improved due to the positive impact of shear and bending. After four passes, the average grain size can be significantly refined to 1.7 μm, and a weaker basal texture can be obtained compared to the initial one due to non-basal slips, dynamic recrystallization (DRX), and twinning. Particularly, the pyramidal 〈c+a〉 slip promotes DRX and twinning. The hardness of the alloy reaches HV 77 as a result of the comprehensive effect of microstructure and texture generated by slip, twinning and DRX competition.

Experimental Study and Neural Network Model to Predict Formability of Magnesium Alloy AZ31B

Magnesium alloy is an emerging smart metal used in various industries like automotive and aerospace industry, due to their lightweight and excellent strength-to-weight ratio. Formability, a critical factor in manufacturing processes, determines the alloy’s ability to undergo deformation without fracture or defects. Fuel economy and environmental conservatives are the key desirable factors in selection of magnesium alloy sheets. Magnesium alloy sheets have low formability at room temperature due to their hexagonal closed-packed microstructures. As the magnesium’s formability at room temperature is considerably low, stretch forming tests are conducted at moderate temperatures. For this purpose, commercially available AZ31B magnesium alloy sheet of 1.1mm thickness has been used and tested at room temperature, 25 degree to within medium temperatures range and at a higher strain rate of 0.01/s. The main objective of an experimental study to predict the formability of magnesium alloy sheets is to gather data through controlled tests and measurements. This data and Forming Limit Diagram (FLD) can be used to analyse the formability of material, it defines failure criteria. On the other hand, using a neural network to predict formability involves training the network on the collected experimental data. Once trained, the neural network can predict the formability of new magnesium alloy sheets based on their characteristics, offering a faster and potentially more accurate prediction method compared to traditional models. This work explores into the realm of regression modelling utilizing neural networks, a powerful subset of machine learning techniques. It begins with a discussion on the setup of machine learning models, emphasizing the crucial steps involved in data preprocessing, model selection, and evaluation.

Fracture behavior of AZ31B magnesium alloy under high-temperature ultrasonic-assisted shearing with related ductile-brittle transformation mechanism

A wide width is one of the fundamental requirements for magnesium alloy sheets to fulfill the lightweight needs of the aerospace and rail transportation industries. Nevertheless, ensuring the dimensional integrity of wide-format magnesium alloy sheets is a challenge in most manufacturing facilities. Simultaneously, processing operations are susceptible to encountering production issues, including but not limited to significant loss of raw materials, elevated costs, environmental contamination, and safety risks. Therefore, to fulfill the operational demands of the hot rolling finishing line for wide sheets made of magnesium alloy, the present study employed ultrasonic-assisted shearing (UAS) to carry out a high-temperature shearing test investigation on the AZ31B magnesium alloy sheet. In this research, we employed scanning electron microscopy, optical microscopy, and a micro-hardness tester to investigate the relationship between ultrasonic amplitude and fracture behavior, deformation mechanism, and mechanical properties of magnesium alloy sheets following exposure to ultrasonic vibration. The fracture morphology of the sheet fracture demonstrates that the behavior of the magnesium alloy sheet fractures under ultrasonic vibration changes from ductile fracture under conventional shearing to brittle fracture under ultrasonic-assisted shearing. The primary cause of this transformation between ductile and brittle is the effect of ultrasonic vibration on the material's internal energy. High-energy ultrasonic amplitude action causes magnesium to absorb a significant amount of ultrasonic energy. This results in an increase in the number of dynamic re-crystallization grains in the material organization, a decrease in the number of twins, and significant refinement of the grains. The sheet's hardness also changes along the rolling and normal directions, with a uniform distribution. The magnesium alloy sheet's fracture quality is optimal when the ultrasonic amplitude is 10 μm in the UAS process. This treatment results in notable enhancements in the section's straightness and brightness. Our study aims to advance the mass manufacturing of wide-format magnesium alloy sheets by investigating a cost-effective and high-yield technique for shearing magnesium alloy sheets.

Preparation of Mg-6Zn-1Y-0.5Zr alloy sheet with excellent mechanical properties and electromagnetic interference shielding effectiveness by extrusion plus rolling

Magnesium (Mg) alloy sheets with excellent mechanical properties and electromagnetic interference shielding effectiveness (EMI SE) have great application prospects. This study investigates the microstructure, mechanical properties, and EMI SE of extruded and rolled Mg-6Zn-1Y-0.5Zr sheets. In the Mg-6Zn-1Y-0.5Zr alloy subjected to extrusion and rolling, the predominant internal second phases are Mg-Zn-Y and MgZn, with the volume fraction of the second phase increasing with cumulative strain. After the extrusion treatment, the average grain size of the Mg-6Zn-1Y-0.5Zr alloy was 2.7 μm. Increasing the rolling reduction to 37% resulted in an average grain size of 5.27 μm, while a rolling reduction to 75% decreased the grain size to 4.06 μm. The Mg-6Zn-1Y-0.5Zr alloys exhibited consistent trends in ultimate tensile strength (UTS), yield strength (YS), and elongation (EL) under extrusion and various rolling strain treatments. These properties showed a relationship with cumulative strain, initially increasing and then decreasing. However, the EMI SE of the Mg-6Zn-1Y-0.5Zr alloy exhibited a positive correlation with cumulative strain. The sheets obtained through a combination of extrusion plus 37% rolling treatment exhibited excellent mechanical properties and EMI SE. The Mg-6Zn-1Y-0.5Zr alloy demonstrated UTS, YS, and EL values of 331.4 MPa, 251.3 MPa, and 18.7%, respectively. The EMI SE in the frequency range of 30–1500 MHz ranged from 79 dB to 113 dB, satisfying the requirements of the electronic information field regarding the mechanical properties and EMI SE of Mg alloy sheets.

Mechanistic investigation of highly bendable magnesium alloy sheet fabricated by short-process manufacturing

In this study, a commercial magnesium alloy AZ31 (Mg-3Al-1Zn-0.3Mn) sheet through a short manufacturing process was found to be ductile and highly formable in bending. Despite possessing a strong basal texture, the short-processed sheet without any annealing can be bent at a small radius, only 0.2 times its thickness in the 90° bending test. Additionally, it could withstand direct deformation by repeated folding-flattening. The in-situ microstructural characterization reveals that extension twin bands with strain localization appear in the bending area. During subsequent flattening, these twin bands underwent detwinning, reducing local strain concentrations and enabling further bending deformation. Such outstanding bend formability originated from the significant 〈a〉-type dislocation loops slipping on the prismatic crystal planes within dynamic-recrystallized grains. These grains underwent a uniform refinement to several microns in the short manufacturing process and exhibited low residual strain. The active prismatic dislocation slip within refined grains was due to its much lower relative activation stress to basal slip (CRSSprism/ CRSSbasal of only ∼1.6) owing to the effective grain boundary hardening. Furthermore, the prismatic dislocation activity was further enhanced when bypassing Al-Mn nano-particles during motion, leaving debris and loops that facilitated easy multiplication.

Enhanced mechanical properties of AZ91 magnesium alloy by asynchronously large-strain high-efficiency rolling with bimodal grain structure

The study describes large strain high-speed asynchronous rolling process to process AZ91 magnesium alloy sheets with an overall thickness reduction of 84 % via two-pass rolling at 350 °C. Rolling speed ratios of 1.0, 1.1, 1.2, and 1.3 were used to obtain bimodal grain structure with different organizational states. Microstructural analysis unraveled that the formation of the bimodal structure was a consequence of combined effect of precipitation-strengthening and the Zener pinning effect. The R3 exhibiting an asynchronous ratio of 1.2 exhibited an optimized bimodal grain structure characterized by smaller recrystallized grains and a more homogeneous distribution. This phenomenon underscored the beneficial impact on enhancing strength and alleviating the anisotropic behavior.

Deformation behaviour, microstructure evolution and dynamic recrystallization mechanism of AZ31 magnesium alloy under co-extruded by Mg-Al composite billet

Conventional methods for hot extrusion of magnesium (Mg) alloy sheets have limitations for microstructure improvement and mechanical property enhancement. Co-extrusion of Mg alloy with an Al alloy core provides an opportunity for refining the grain size and improving basal texture. This study introduces a novel severe plastic deformation (SPD) method, Direct Extrusion-Continuous Shear (DE-CS), utilizing 6063 Al alloy as the core to fabricate innovative Mg/Al clad composite sheets. Monolithic Mg sheets (non-co-extruded condition) are extruded under identical conditions for comparison. By evaluating the microstructure and mechanical properties of AZ31 Mg alloy under co-extrusion and non-co-extrusion conditions, the positive effect of Mg-Al composite billet co-extrusion on AZ31 Mg alloy is established. The grain refinement effect in co-extruded samples is superior, enhancing plasticity without significant reduction in tensile strength. The microstructure evolution and dynamic recrystallization (DRX) behaviour of AZ31 Mg alloy during co-extrusion were analyzed comprehensively. The results indicate that, in the initial stages of deformation, various variants of {10−12} extension twins (ETs) play a crucial role in refining the original grains, forming initial [10−10]//ED fiber texture components alongside other non-basal components. Upon entering the shear deformation (SD) zone, deformed twins disappear, and small dynamically recrystallized (DRXed) grains emerge along boundaries of coarse deformation grains and within the grains. Strong shear deformations and compressive stress from transverse direction (TD) induce intensified prismatic <a> and pyramidal <c+a> slip, promoting continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX). CDRX predominantly affects elongated deformed grains, forming an [10−10]//ED fiber texture through high-energy grain boundary segmentation. Subsequently, compatible stress increases due to the activity of non-basal slip dislocation and the reduction in grain boundary (GB) size. DDRX emerges as the dominant mechanism, generating randomized [10−10]//ED fiber and non-fiber textures within parent grains and at boundaries.

Correction to: Dependence of Microstructure Evolution and Mechanical Properties on Loading Direction for AZ31 Magnesium Alloy Sheet with Non‑basal Texture During In‑Plane Uniaxial Tension

Correction to: Dependence of Microstructure Evolution and Mechanical Properties on Loading Direction for AZ31 Magnesium Alloy Sheet with Non‑basal Texture During In‑Plane Uniaxial Tension

Effect of adhesive on friction stir spot welding of AZ31B magnesium alloy sheets

ABSTRACT AZ31B magnesium alloy sheets were lap-joined with adhesive only, friction stir spot welding (FSSW) only, and also with FSSW after adding adhesive between sheets. The produced joints were comparatively studied regarding joint cross-section geometrical features and defects that occurred at joint interface, microstructure, microhardness, tensile shear strength, and fracture surface evaluation. For joints made with FSSW only, cracks formed at underside of top sheet just above interface of sheets. However, joining with FSSW while there is adhesive between sheets eliminated formation of cracks and enabled weld width to enlarge significantly. Additionally, adhesive presence at interface of sheets joined by FSSW drastically reduced hook defect formation in the weld . The hook sizes of joints of FSSW with adhesive were so small as to be negligible compared to those of FSSW adhesive-free. Consequently, joints of FSSW with adhesive had much higher tensile shear strength. However, due to their brittle fracture, they displayed much less ductility than adhesive-free FSSW joints. The joints made via just adhesive had the lowest strength and elongation. Microstructure and microhardness of joints made by FSSW without and with adhesive were slightly different from each other. The main factors determining joint strength were adhesive, hook and weld size.

Refining grain structure and improving elongation properties in AZ31 magnesium alloy sheets using hard plate accumulative roll bonding

Magnesium alloy sheet are an ideal choice for achieving material and structural light weighting. Traditional ARB technology can significantly reduce the size of magnesium alloy sheet, but it is faced with the challenge of strong plastic inversion. In addition, it is easy to produce edge cracking defects, and it is also difficult to control the quality of the sheet. In this study, we prepared AZ31 magnesium alloy sheet by HP-ARB process for the first time. The results show that compared to ARB, the HP-ARB sheet has remarkable improvements in and mechanical properties.After two passes, the average grain size of HP-ARB decreased from 6.19 μm to 4.58 μm, tensile strength reaches 291 MPa, and the elongation is 10.1%, which significantly increased to 55.4% compared with ARB. HP-ARB has the ability to transform part of shear stress into compressive stress, which improves the stress distribution on the sheet. On one hand, a large amount of energy stored in dislocations provides energy for DRX, which makes the process more complete, leading to microstructure refinement and grain orientation randomization. This leads to the deviation of texture orientation to TD direction, which leads to the decrease of pole density and weakening of the strong basal texture. On the other hand, dislocation density (ρD) of the sheet is relatively low. The average Schmidt factor of prismatic <a> slip and pyramidal <c+a> slip in the HP-ARB process is higher, which is beneficial to dislocation slip, thus promoting an increase of sheet elongation. This provides a new strategy for the forming and manufacture of high performance magnesium alloy sheet.

A study on the tribological behavior of AZ31 magnesium alloy sheets processed by temperature-assisted ultrasonic shot peening

Mg alloy, as a promising lightweight structural material, finds applications in various fields. However, poor surface properties like wear resistance greatly limit its applications. As a surface modification technology, ultrasonic shot peening (USP) has gained significant popularity. In this study, temperature-assisted USP (TA-USP) was firstly applied to AZ31 Mg alloy. The influence of peening duration and temperature on microstructural evolution and mechanical properties was investigated in details. The ball-on-disk dry sliding wear test was performed to examine the tribological behavior. The results show that a gradient microstructure and surface nanocrystallization are introduced by TA-USP. The gradient becomes significantly pronounced as the peening duration extends. The surface hardness increases from the as-annealed 60.9 ± 1.8 HV to 159.0 ± 6.1 HV after processed at room temperature with 800 s, and a depth of about 600 μm for the affected region is achieved. When the peening temperature is raised, the gradient weakens, even disappears at 300 °C, and the hardness decreases. Notably, the gradient microstructure and enhanced hardness exhibit significant thermal stability below 200 °C. The wear curves and morphology analysis suggest that TA-USP obviously improves wear resistance. The surface nanocrystalline results in an easy formation of MgO patches and reduces the coefficient of friction. Moreover, the presence of gradient microstructure also retards the delamination phenomenon. Increasing peening duration or temperature to a moderate level will lead to an enhanced wear resistance, owing to its dependence on both hardness and toughness. A simplified wear transition map is roughly established to predict optimum wear resistance.

AZ91 magnezyum alaşımlarının sürtünme karıstırma nokta kaynağı;eksenel kuvvet ve dönme hızının kaynak kalitesine etkisi ve muayene planlamasına ilişkin bir yaklaşım

In this study, the friction stir spot welding (FSSW) process for the magnesium alloy (AZ91) sheet materials are investigated. Friction stir spot welding (FSSW) is a solid-state welding process and one of the innovative methods to join specifically automotive components. Recently magnesium alloys are promising materials where combination of high strength and low density can be observed to improve vehicle performance and reduce emissions and fuel consumption in structural materials for automotive applications. A finite element model (FEM) established to understand the effect of axial force and rotational speed during the simulation in automotive applications. The FEM investigates the effect of axial force ranging from 1 kN to 8 kN and rotational speeds of 1000 rpm - 4000 rpm. The model analyses the heat flux and the temperature rise that leads defect formation after the process. 4.5 kN, 6 kN and 8 kN axial forces and 3000 rpm-4000 rpm rotational speeds are evaluated as the critical values in terms of defect and crack formation during the process under specified boundary conditions. Finally, several non-destructive inspection methods are suggested to secure structural integrity after the FSSW process to eliminate the harmful effects of surface and volumetric discontinuities.

Predictive assessment of the ultrasonic shearing quality of AZ31B magnesium alloy sheet based on coupled vibration-thermal model

Predictive assessment of the ultrasonic shearing quality of AZ31B magnesium alloy sheet based on coupled vibration-thermal model

Preparation of Mg–6Zn–1La-0.5Zr alloy sheet with excellent mechanical properties and electromagnetic interference shielding effectiveness by extrusion plus rolling

In the field of specialty electronics and communications, there is a critical demand for magnesium (Mg) alloy sheets that possess exceptional mechanical properties and electromagnetic interference shielding effectiveness (EMI SE). This paper aims to develop a cost-effective and straightforward process for preparing a research proposal that combines excellent mechanical properties and EMI SE. After undergoing extrusion treatment, the Mg–6Zn–1La-0.5Zr alloy demonstrates an apparent bimodal microstructure, with an average grain size of approximately 2.55 μm. Subsequently, following a 37% rolling treatment, the grain size increases to about 5.29 μm. This increase in grain size is attributed to grain growth resulting from holding prior to the multi-pass rolling treatment. Notably, the Mg–6Zn–1La-0.5Zr alloy, subjected to extrusion and 75% rolling treatment, exhibits remarkable mechanical properties and EMI SE, with ultimate tensile strength (UTS), yield strength (YS), and elongation (EL) values of 337.5 MPa, 227.3 MPa, and 12.5%, respectively. Furthermore, the EMI SE ranges from 79 dB to 110 dB within the frequency range of 30–1500 MHz. The exceptional mechanical properties are attributed to the synergistic effects of various strengthening mechanisms, including grain boundary strengthening, second phase strengthening, dislocation strengthening, heterogeneous deformation-induced strengthening, and texture. Similarly, the superior EMI SE is attributed to the alloy's higher electrical conductivity, strong basal texture, and uniformly diffused second phase.

Surface quality enhancement of warm incremental forming process using solid lubricant with varying etching period

The warm incremental forming process is an effective and flexible approach for forming magnesium alloy (AZ31B) sheets, which usually is difficult to deform at room temperature. However, friction increases drastically at elevated temperatures during the forming process. In order to reduce friction, liquid lubricants are generally applied on the sheet’s surface; however, the liquid lubricant usually thins out during the warm incremental forming process. To address this problem, solid lubricants such as graphite and molybdenum disulfide have been used as better alternative lubricants for forming the parts at elevated temperatures. In addition, an increase in surface roughness, either by depositing porous film or by creating micro or nanostructures, can help better the surfaces’ lubrication by solid lubricants. In this work, a facile etching method is used to treat a pre-formed sheet and solid lubricants to improve the surface quality and reduce the part’s wear during the warm incremental forming process. The combined effect of the type of solid lubricant and etching time is studied in detail. The quality of the magnesium alloy sample and its morphology before and after the forming process has been examined using various characterization tools, including a surface roughness tester, a tribometer, and scanning electron microscopy (SEM). The results reveal that the magnesium alloy sample etched for 5 min and lubricated with graphite powder showed significantly low weight loss and better surface quality. Overall, the results revealed that the etching of samples could be highly beneficial for the warm incremental forming process.

Local twinning behavior of ZK61m magnesium alloy sheet under multiaxial stress during drawing-pressing with Erichsen test machine

In order to find a more effective method to preset twins and to explore the microstructure and twin evolution of magnesium alloy sheet under multi-axial stress state deformation, drawing-pressing deformation with Erichsen test machine is used as a sheet processing method to process ZK61m magnesium alloy sheet in this experiment. During repeated drawing-pressing deformation, the central area of the plate was subjected to annular tensile and compressive stress. In the process of deformation under unidirectional force, the slip direction of some grains is in hard orientation and it is difficult for the slip to operate, while the annular tensile and compressive stress state will provide the grains with multidirectional slipping options. Electron back-scattered diffraction (EBSD) technique was used to analyze the microstructure of magnesium alloy plates with different drawing-pressing times and different positions from local deformation center to edge. In this study, the complex circumferential force environment will weaken the anisotropy of deformation structure during repeated drawing-pressing, and the effect of prefabricated twins is more obvious. Based on the modified generalized Schmid factor (GSF) analysis, it is easier to show a variety of twin variation behaviors within a grain during Erichsen deformation. After the plate is deformed by Erichsen processing, the mechanical properties of magnesium alloy sheet have also been effectively improved.

Effect of neutral layer migration on bending force of AZ31B magnesium alloy sheet during bending

In this paper, they are based on the micro-element stress equilibrium condition in the plastic deformation theory and the Yoon-2014 yield criterion, which can reflect the tension and compression asymmetry of AZ31B magnesium alloy, a bending force model is established to predict the required bending force at different angles according to the neutral layer migration in the bending process of magnesium plate. The offset and bending force values of the neutral layer were verified by FEM and corresponding experiments. The results show that the bending force of a magnesium plate is related to the geometrical size of the scale, the yield limit of the material, and the height of the elastic zone of deformation. The model’s prediction accuracy is better than that of the conventional calculation formula, which can realize the reliable prediction of the required bending force of the magnesium plate. In the bending process, the magnesium plate is affected by the asymmetry of tension and pressure, and the neutral layer migrates to the tensile side. The deviation degree of the neutral layer is the most obvious when the magnesium plate is bent to 90°, and the required bending force is the largest.

Finite element simulations and experimental investigations on formability of magnesium alloys in superplastic forming

The paper presents the formability aspects of magnesium alloy (AZ31B) sheets into regular and intricate shapes during Super Plastic Forming (SPF). Finite Element (FE) simulations are performed at specific strain rates within the superplastic temperature range. The formability of 1 mm sheet into conical, cylindrical, box and groove shaped dies are simulated. The simulated Pressure-Time (P-T) curve is given as pressure control algorithm to form the shapes experimentally. Thickness strains of the experimentally formed components validated with simulation results are found to be in close agreement with each other. It is demonstrated by the analysis that regular shapes posses uniform thickness distribution throughout the profile. The components with complex intricate shapes recorded unevenness in thinning behavior. The unevenness in thinning is influenced by the Grain Boundary Sliding (GBS) and diffusion kinetics. GBS is well controlled by optimum P-T algorithm to produce sharp intricate shapes with uniform thickness.