AZ31B Magnesium Alloy Sheet Research Articles

Investigating formability of AZ31B magnesium alloy sheet with different texture and thickness in combination of the Erichsen experiment and CPFEM model

In this study, the formability of the AZ31B magnesium alloy sheets was investigated in combination of experiment and CPFEM modelling. The deformation mechanisms during the Erichsen forming were revealed and the effect of the related parameters were discussed. It was shown that the simulation results based on the normalized Cockcroft-Latham criterion are consistent with the experimental results. The maximum stress and strain concentrate at the center of dome, and exhibit an elliptical distribution shape. The difference of asymmetry situation between the sheets results from the different textures. The basal <a> slip is the dominant mode, and the prismatic <a> slip is also active to accommodate plastic strain in sheet plane. The relative activity of the pyramidal <c+a> slip is low, but very effective to accommodate the plastic strain in thickness direction. The sheet with higher relative activity of the prismatic <a> and pyramidal <c+a> slips exhibit higher formability. The sheet thickness influences the formability through changing the stress-strain response, as well as the orientation-relationship between stress state and grains which can affect the deformation mechanisms. The formability depends on the plastic strain accommodation ability that is comprehensively related to the averaged plasticity, orientation-relationship between stress state and grains, r-value and n-value. CPFEM modeling is convenient pathway to predict the formability.

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.

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.

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

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.

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.

底面集合組織の形成を抑制したAZ31Bマグネシウム合金板材の室温深絞り成形性に及ぼすプロセス因子の影響

The effects of process parameters on room-temperature (RT) deep drawability were investigated for AZ31B magnesium alloy sheets, in which the formation of basal texture was suppressed by high-temperature rolling. When the blank holder force was set to the minimum value to prevent wrinkling, high RT drawability was obtained. In particular, a significantly high limiting drawing ratio (LDR) of 1.83 was obtained by the optimization of the process parameters of the servo-press machine. At higher punch speeds, the drawability tended to be deteriorated; however, a high LDR of 1.72 was obtained even at a high punch speed of 50mm/s by the optimization of the process parameters of the servo-press machine. Furthermore, when the punch speed in the initial stage of deep drawing was reduced, it was possible to perform deep drawing without fracture even if the punch speed in the later stages was increased. The results of the study of the effect of lubricants indicated that relatively high RT drawability was obtained when molybdenum disulfide was utilized. It was also suggested to be important to select a lubricant that reduces punch load and does not delaminate during deep drawing.

Unusual Spreading of Strain Neutral Layer in AZ31 Magnesium Alloy Sheet during Bending.

In this work, we reported an unusual phenomenon of strain neutral layer (SNL) spreading in an as-rolled AZ31B magnesium alloy sheet during V-bending. The SNL on the middle symmetrical surface perpendicular to the transverse direction (TD) of the sheet extended to the compression region and was accompanied by a mound-like feature. However, the SNL on the side surface perpendicular to the TD was distributed with a parallel band feature. The underlying mechanism was revealed by the finite element (FE) analysis. The results indicate that the three-dimensional compressive stresses in the compression region of the bending samples were responsible for the above phenomenon. Moreover, the area of the SNL in the middle position gradually decreased as the bending test progressed. The findings in this study provide some new insights into the bending deformation behavior of magnesium alloy.

Forming limit of AZ31B magnesium alloy under in-plane complex biaxial loading paths with cruciform specimens

This paper focused on the forming limit curves (FLC) of the AZ31B magnesium alloy sheet metal under different complex loading paths in-plane. Compared with simple loading paths, the study of forming limit of sheet metal under complex loading paths was more practical. In this study, biaxial tensile test of the cruciform specimen was utilized to acquire the FLC after the cruciform specimen was subjected to uniaxial pre-tensile process along rolling direction, which experimentally characterize the forming limits under different pre-strain values of 1.15%, 2.34%, 4.0%, and 5.4%. Subsequently, based on the constitutive model, Hill48 yield criterion and shear failure criterion, the theoretical FLCs of AZ31B magnesium alloy sheet metal was be calculated. Meanwhile, the normal biaxial tensile tests were also simulated by Abaqus to obtain the limit strains by Finite Element Analysis (FEA). Extracting limit strains from the fracture region in FEA model when the first derivative of the strain difference with respect to time reached the maximum value between the first principal strain of necked element and the first principal strain of the element adjacent to the necked zone. As a result, the experimental FLCs was qualitatively consistent with the result of theoretical model and FEA model. In addition, the FLCs of AZ31B magnesium alloy sheet moved to the upper left of forming limit diagram with the increase of the pre-strain, which indicated that the pre-strain process along the rolling direction could significantly improve the formability of the sheet metal.

Influences of stress states and loading directions on the anisotropic fracture of magnesium alloy AZ31B sheet under tension-dominated forming conditions

Influences of stress states and loading directions on the anisotropic fracture of magnesium alloy AZ31B sheet under tension-dominated forming conditions

Drillability of Magnesium-Based Fiber Metal Laminates Obtained via Hot Metal Pressing with Different Metal Surface Treatments

The demand for lighter and more performant aerospace and automotive components has resulted in a substantial surge in a recent interest in parts made of Fiber Metal Laminates (FMLs). For such components, drilling operations are crucial for permitting subsequent assembly. However, drillability of fiber metal laminates is critical due to the heterogeneous thermal and mechanical properties of the metal and composite that form the laminate. In this framework, the current research work aims at understanding how drilling operations can be affected by different surface treatments carried out on AZ31B magnesium alloy sheets joined with Glass Fiber Reinforced Polyamide 6 (PA6-GFRP) via hot metal pressing to form the FML. To this end, the Mg/PA6-GFRP/Mg composites were first fabricated using AZ31B surfaces that were previously treated through sandblasting, annealing, and their combination. Dry drilling was then performed using twist and spur drill bits. The feed was also varied, using two levels. The thrust force, hole quality, delamination and fiber pull-out were considered to evaluate the FMLs drillability. Results showed that the magnesium alloy sheet treatment influenced the drillability, and that the drill bit had an effect too. In particular, sheets that were both sandblasted and annealed allowed the highest drillability avoiding delamination. The use of spur drill bits improved the drillability too, reducing the FML inflection under the drill bit load.

Mechanical Behaviour of Magnesium Alloy Based - Fiber Metal Laminates after Fabrication Using Different Metal Surface Treatments

This paper presents an experimental investigation of the mechanical response and failure mode of magnesium alloy-based Fibre Metal Laminates (FMLs) having different surface pretreatments under axial compression loading conditions. To improve the interfacial bonding strength between the metal and composite layers, three categories of samples were fabricated by hot pressing using sandblasted, annealed and both sandblasted and annealed AZ31B magnesium alloy sheets. To evaluate the bonding strength along the shear and normal directions, single lap shear tests and T-peel tests were conducted. It was found that the combination of sandblasting and annealing can greatly enhance the shear and normal interfacial bonding strength compared with only sandblasting and annealing, separately. To assess the effect of the interfacial bonding strength on the FML compressive performance, quasi-static buckling tests were performed at varying surface treatments of the magnesium alloy sheets. The analysis of the load-stroke curves and failure modes indicates that delamination can significantly reduce the buckling capability and structural stability, and that the improvement of interfacial bonding strength can dramatically strengthen the FML compressive capability.

Impact of power modulation on weld appearance and mechanical properties during laser welding of AZ31B magnesium alloy

A new laser welding process with power modulation was proposed to promote the weld formation and improve the quality of welds over magnesium alloys. The impact of the parameters of power modulation on laser welding was investigated experimentally at the aspects of weld formation, keyhole entrance, molten pool flow, and microstructure and mechanical properties of welds. The experiments were performed for the butt joints on AZ31B magnesium alloy sheets with a thickness of 3 mm, and the results shown that the laser welding with a sinusoidal power modulation increased the melting volume and improve the efficiency of energy coupling in comparison with that with a constant power. Power modulation in laser welding could minimize even eliminate the underfill over the top surface of weld. The higher the frequency of power modulation was, the longer the columnar grains formed near the fusion line of weld. With an increase of the amplitude of power modulation, both of the cell grains and columnar grains were decreased in width; while the average size of equiaxed grains was increased. Power modulation in laser welding improved the tensile strength and the elongation of magnesium alloy at welds; when the power was modulated with the frequency of 200 Hz and the amplitude of 300 W, the maximum tensile strength was 237 MPa, and the ultimate elongation was 7.26% and the weld was broken by a mixed ductile–brittle fracture.

Strain Rate and Temperature Effects on Formability and Microstructure of AZ31B Magnesium Alloy Sheet

Magnesium alloys play an important role in lightweight structures, which are extensively used in different industries due to their excellent mechanical and physical properties. In this paper, the formability of the AZ31B magnesium alloy sheet was studied by using tensile tests at different temperatures (from 25 to 250 °C) and strain rates (from 0.017 s−1 to 0.34 s−1). The results showed that the material behaves with positive temperature sensitivity when forming at a temperature lower than 200 °C. The effect of the strain rates on the formability of AZ31B was larger at high temperatures. The metallography of AZ31B at different temperatures and strain rates was observed by OM. The results showed that the partially recrystallized structure was exhibited at a temperature of 150 °C. With the increase in temperature, the approximate complete recrystallization was exhibited at a temperature of 250 °C. The fracture morphology of AZ31B was observed at different strain rates and temperatures by SEM. Additionally, the main fracture pattern was quasi-cleavage at room temperature. However, with the increase in temperature, the fracture pattern was transited from a quasi-cleavage pattern to a ductile fracture pattern. The ductile fracture pattern was the main fracture pattern at a temperature of 250 °C.

Numerical simulation and experimental study of warm hydro-forming of magnesium alloy sheet

The uneven forming temperature during warm hydro-forming of magnesium alloy sheets is one of the main causes of defects in formed parts. In order to completely solve this problem to obtain products with good forming quality, a new warm forming method for magnesium alloy sheet is proposed: the magnesium alloy sheets and forming die are immersed in hot oil to achieve constant temperature forming. In addition, a hot oil warm hydro-forming device for magnesium alloy sheets was designed and developed. This work also carried out the numerical simulations and forming experiments, this study to investigated the effects of forming concave die chamfer, temperature, friction coefficient, hydraulic pressure, and blank holder force on the warm hydro-forming of magnesium alloy sheet. The simulation results are in good agreement with the experimental ones, and the feasibility of warm hydro-forming of magnesium alloy sheet is verified. According to the numerical simulations and forming experiments, the best process window for warm hydro-forming of l mm thick AZ31B magnesium alloy sheet was obtained. The hot oil constant temperature hydraulic forming technology can enrich the forming process of magnesium alloy and provide a new perspective and technical basis for warm forming of other hard-to-deform metal materials.

Experimental and Simulation Analysis of Warm Shearing Process Parameters for Rolled AZ31B Magnesium Alloy Plate

The study was carried out on a KRUMAN-CLS1016-NC shearing machine at a shear temperature of 20 °C to 250 °C and a shear edge clearance of 8% to 10% for a rolled AZ31B magnesium alloy plate with a thickness of 8.35 mm. The height and area share of the bright zone in the shear section were analyzed by macroscopic measurements and super depth-of-field experiments, and combined with DEFORM-3D finite element simulations, the optimal shear program was determined using the orthogonal experimental method. It was found that, with the increase of shear temperature and shear edge clearance, the height and area of the burnish band first increased and then decreased. In addition, from the simulated orthogonal test, it can be obtained that the effect of shear temperature on the height of the burnish band is superior to that of the shear edge gap, so the selection of shear temperature is preferred. In this paper, the shear temperature of 150 °C and the shear edge clearance of 12% were finally determined as the best shear process parameters for the rolled AZ31B magnesium alloy sheet.

A bulge-test based viscoplastic model for superplastic deformation behaviour of a magnesium alloy

In this work, a new approach is proposed for modelling the superplastic deformation of AZ31B magnesium alloy sheets. Gas bulge tests were performed at 450 ℃ under three constant gas pressure levels of 0.4, 0.7, and 1.0 MPa. The dome height evolutions according to time were recorded in experiments and then translated into stress–strain curves using a new analytical approach. In order to predict the superplastic behaviour of the material, the Variable m-value Viscoplastic (VmV) model was considered in this study, whose constants were directly assessed from the bulge test results. The bulge forming of the magnesium alloy sheet was simulated with ABAQUS/Standard using the VmV model. The predicted dome height-time profiles and thickness distributions along the specimens were compared with the experimental results. Finally, a real case study (a resorbable cheekbone prosthesis) was simulated implementing the VmV model for validation purposes. The results from the simulation of both the bulge tests and the case study manufacturing revealed that the proposed model is able to effectively reproduce the superplastic behaviour of the AZ31B magnesium alloy.

Process optimization and mechanism analysis on electropulse-assisted incremental forming of AZ31B magnesium alloy sheet

Process optimization and mechanism analysis on electropulse-assisted incremental forming of AZ31B magnesium alloy sheet

The tensile deformation behavior of AZ31B magnesium alloy sheet under intermittent pulse current

In this paper, to investigate the effect of loading method of pulse current on the tensile deformation behavior of AZ31B magnesium alloy sheet, the intermittent pulse current with short-time and high-frequency was introduced in uniaxial tensile tests and the influence of duty ratio and loading time of pulse current on the deformation behavior of AZ31B magnesium alloy sheet was discussed. The strain and temperature field distributions on the specimens were measured during the intermittent pulse electrically-assisted tension (IPEAT), and the microstructure and fracture morphology under different pulse current conditions were observed. Results shows appropriate pulse current parameters can effectively improve the elongation of AZ31B magnesium alloy sheet. The strain of the sample is closely related to temperature distribution. With the deformation of the sample, the temperature on the sample increases gradually and the temperature distribution is non-uniform along the tensile direction, resulting in an inhomogeneous strain distribution of the sample. In addition, grain growth and dynamic recrystallization were observed on the AZ31B magnesium alloy sheet in different degrees under intermittent pulse current. Fracture morphology analysis shows that the number of dimples and tearing edges increased on the fracture obtained under IPEAT. The microhardness analysis shows that when intermittent pulse current is applied in the tensile test, the hardness of the sheet may change. This research provides an effective idea for the forming process of magnesium alloy sheets, which can be used to form large size thin-walled sheet components, and can significantly improve the forming quality of the sheets.