Formability Of Magnesium Alloy Sheets Research Articles

Enhanced stretch formability of AZ31 magnesium alloy sheet by secondary regulation of initial twin orientation

• Simple shear deformation is introduced to regulate twinning texture. • The twin orientation rotates away from the transverse direction, due to shear deformation. • The regulated twin orientation still exists after annealing. • Based on the modification of grain orientation, the formability is greatly improved. To modify the basal texture and improve the formability of the magnesium alloy sheet, in-plane shear deformation is introduced into the pre-twinned AZ31 Mg alloy sheet. The twinning orientation is secondary regulated and rotates away from the transverse direction about 20° after shear deformation. After annealing, the recrystallized grains inherit the grain orientation of rotating twins. Thus, the basal texture is significantly weakened. Compared with the received sample, the average fracture elongation of sheared and annealed sample improves from 15.3 % to 28.5 %. The Erichsen value increases from 2.79 mm to 5.63 mm due to the secondary regulation of initial twin orientation (SRITO).

Experimental study and machine learning model to predict formability of magnesium alloy sheet.

Background: Magnesium alloy is not only light in weight but also possesses moderate strength. Magnesium AZ31-H24 alloy sheet has many applications in the automotive and aerospace industries. Experimental stretch forming tests are performed on this sheet to measure the material's formability by constructing forming limit diagrams. Methods: Several tests of Nakazima were carried out on rectangular samples at 24, 250, 350°C and 0.01, 0.001 mm/s using a hemispherical punch. The work done to predict the formability of magnesium alloys has not been recorded in recent literature on machine learning models. Hence, the researchers of this article choose to explore the same and build three models to predict the formability of magnesium alloy through Random Forest algorithm, Extreme Gradient Boosting, and Multiple linear Regression. Results: The Random Forest showed high accuracy of 96% in prediction. Conclusions: It is concluded that the need for physical experiments can be greatly minimized in formability studies by using machine learning concepts.

The role of {10–12} tensile twinning in plastic deformation and fracture prevention of magnesium alloys

To improve the formability of magnesium alloy sheets, {10–12} tensile twins can be used to improve the plastic deformation ability of magnesium alloys at room temperature. In this paper, through the quasi-in-situ study of the AZ31B magnesium alloy samples prepared with {10–12} tensile twins during the uniaxial tensile process, the mechanism of tensile twinning to improve the plastic forming of magnesium alloys is further explored. The results show that the variant selection behavior of the tensile twin usually exhibits Schmid behavior, but sometimes non Schmid behavior, which leads to the change of the matrix grain orientation and the activation of the pyramidal II < c+a > slip more easily. Strain compatibility is the main factor affecting the variant selection behavior of transgranular twins, while the activation of the pyramidal II < c+a > slip of the matrix is almost geometric compatibility. The pyramidal II < c+a > slip is easily activated inside the twin, and its activation is determined by the strain compatibility between adjacent grains. Microcracks propagate along the grain boundaries with poor strain compatibility. Tensile twinning can coordinate the slip between adjacent grains and the strain transfer between twins, improve the strain compatibility between adjacent grains, and reduce microcrack propagation.

Microstructure, mechanical properties and stretch formability of as-rolled Mg alloys with Zn and Er additions

The magnesium alloy has a unique advantage in 3C fields due to its high specific strength and excellent electromagnetic shielding characteristic. However, it is difficult to deform homogeneously because of hexagonal close-packed structure. In the present work, the microstructure, mechanical properties and stretch formability of magnesium alloy sheets with different alloying elements were investigated. It was indicated that a trace addition of Zn or/and Er made a key role in modifying texture, activating shear bands formation and precipitating nanoscale second phases, respectively, which resulted in an obvious improvement in both stretch formability and mechanical properties. The results suggested that the Mg–0.5Zn–0.5Er alloy sheet exhibited higher tensile strength along the rolling direction, i.e., yield strength of 180 MPa and ultimate tensile strength of 201 MPa, accompanying with superior Erichsen value of 7.0 mm at room temperature. The good performances of the sheet were ascribed to weakening basal texture intensity, formation of shear bands and precipitation of nanoscale W-phase (Mg3Zn3Er2). The microstructure, mechanical properties and stretch formability of magnesium alloy sheets with different alloying elements were investigated in the present investigation. It was indicated that a trace addition of Zn or/and Er made a key role in modifying texture (Fig. 1), activating shear bands formation and precipitating nanoscale secondary phases (Fig. 2), respectively, which resulted in an obvious improvement in both stretch formability and mechanical properties (Fig. 3).

A Further Improvement in the Room-Temperature Formability of Magnesium Alloy Sheets by Pre-Stretching.

Pre-stretching experiments were carried out on AZ31–0.5Ca magnesium alloy to alter the microstructure and texture for enhancing room-temperature formability. Compared to as-received alloy, the formability of a 5%-stretched sample was improved by 15%. This was attributed to enhanced strain hardening capability related to the weakening of basal texture and less homogeneous microstructure. In addition, in-grain misorientation axis analysis performed on the samples (as-received and stretched) also confirmed the higher activity of the non-basal slip systems in the 5%-stretched sample.

Study on the Formability of Magnesium Alloy Sheets in the Incremental Forming Process with External Heating Sources

Magnesium alloy sheets have low formability at room temperature due to their hexagonal closed-packed microstructures. In order to increase the formability of magnesium alloy sheets (AZ31) and fabricate a complex geometry, an incremental forming process with external heat sources such as the near-infrared heater and heated tools can be employed. Cylindrical cup shapes and Pyramidal cup shapes with various angles were fabricated to find out the formability limits. The maximum formable angle of the cylindrical cup shape increased from 20° at the room temperature to 72° by employing the incremental forming process using two external heat sources. It means that the temperature of AZ31 was increased to a proper forming temperature very efficiently.

Experimental analysis of AZ31B magnesium alloy sheet failure using punch stretching

The formability of magnesium alloy sheets at room temperature presents anisotropy in mechanical properties and difficulties in terms of occuring cracks easily, especially in regions with bend radius. In addition, the elastic spring-back is significant, leading to massive deviations from the desired shape. Recent studies conducted in this field lead to stretch forming magnesium alloys sheets using thermo-mechanical treatments at temperatures up to 400°C. The present study was conducted on 1 [mm] thick magnesium alloy AZ31B sheet to investigate its formability when stretching at room temperature by several dies with different radius. The stretching process was conducted on a hydraulic press, using 3D printed PLA dies with the following values: R180, R320, R540, R720, R900 and R1080. The samples were stretched until fracture to highlight the fracture force, distance to fracture, deviation from the die radius and bend angle.

Enhanced Stretch Formability of Magnesium Alloy Sheet by Prestretching at Various Speeds at Higher Temperature

Prestretch deformation of 6.48% with various initial speeds (1 mm/min, 101 mm/min, and 100 mm/min) was carried out at 723 K to improve the formability of AZ31 Mg alloy sheet. After prestretching, the (0001) basal texture weakened with increase in the speed owing to activation of nonbasal slips during deformation, while the yield strength and anisotropy decreased simultaneously. Owing to the basal texture weakening, the Schmid factors of the basal slips and strain-hardening coefficient increased, while the Lankford value decreased, enhancing the stretch formability of the AZ31 Mg alloy sheet. In addition, the Erichsen value was improved from 2.48 mm for the as-received alloy to 4.36 mm for the sample prestretched at 100 mm/min (an enhancement of 75.8%). This may provide a new approach for industrial production of Mg alloy sheets with weakened basal texture and improved formability by applying a smaller prestrain at higher temperature.

Improved Stretch Formability of AZ31 Magnesium Thin Sheet by Induced {10–12} Tension Twins

In order to improve the stretch formability of magnesium alloy sheets, {10–12} tension twins were introduced by pre-compression along the rolling (RD) and transverse directions (TD) with 1.6%, 3.3%, and 5.4% strain levels. Subsequent annealing at 473 K was conducted for 6 h to preserve twinning lamellae. In order to avoid bending–buckling, a special fixture for thin sheet compression has been developed. In addition, hemispherical tests were performed at room temperature. The mechanical properties were improved, while the Lankford value (r-value) decreased and the strain hardening exponent (n-value) increased as the pre-compression level increased compared with the as-received sheet. The stretch formability was also improved. The Erichsen value was dramatically improved the most, from 2.83 mm in the as-received to 5.36 mm and 6.78 mm in TD and RD pre-compressed 5.4% Mg specimens, respectively, which increases by 89% and 139%. The stretch formability was enhanced much more with the pre-compression along the RD as compared to the TD.

Enhanced room temperature formability of magnesium alloy sheets by suppression of basal texture formation

Magnesium (Mg) alloys are suitable materials for weight reduction in vehicles because of their low densities and high specific strengths. However, rolled Mg alloy sheets generally exhibit a poor formability at room temperature and thus their applications are restricted. This poor formability is originated from basal slip dominated deformation as well as strong basal texture. It is known that the formability can be improved by suppression of basal texture formation. Thus, large efforts have been devoted to texture control for the purpose of enhancing the room temperature formability. In this paper, our recent researches for texture control of rolled Mg alloy sheets are reviewed.

Processing Effects on the Formability of Magnesium Alloy Sheets

As a generalized semi-finished product, the use of magnesium sheets requires addressing two major aspects of their processing: their microstructure and texture control, which are both essential for the forming behavior of such sheets during their forming to parts. Further, the processing of such sheets is complex, and therefore expensive, and requires simplification. In this work, magnesium alloys AZ31, ZE10, and ME21 are investigated in the form of conventionally rolled sheets, as well as in the form of extruded sheets. Their microstructural and textural development are correlated to their mechanical and forming properties. During extrusion, strong textures develop that hinder stretch-forming operations, even in rare earth-containing alloys. Chemical composition and process parameters have a significant impact on the texture development, and enable the design of sheet materials with weak textures and potentially enhanced formability.

Residual-stress-induced grain growth of twinned grains and its effect on formability of magnesium alloy sheet at room temperature

A magnesium alloy sheet was subjected to in-plane compression along with a vertical load to avoid buckling during compression. Pre-compressed specimens machined from the sheet were annealed at different temperatures and the changes in microstructure and texture were observed using electron back scattered diffraction (EBSD). Twinned grains preferentially grew during annealing at 300°C, so that a strong texture with the <0001>direction parallel to the transverse direction developed. EBSD analysis confirmed that the friction caused by the vertical load induced inhomogeneous distribution of residual stress, which acted as an additional driving force for preferential grain growth of twinned grain during annealing. The annealed specimen showed excellent formability.

Modified texture and room temperature formability of magnesium alloy sheet by Li addition

The effect of Li addition on the mechanical responses of magnesium alloy sheets was examined in correlation with the concurrent microstructure and texture evolution. The basal texture was drastically weakened and the basal pole rotated to the transverse direction (TD) owing to the Li addition. The Mg alloy sheet containing lithium element exhibited larger uniform elongation and its Erichsen value (IE) increased by ~ 59 %. Enhanced the ambient formability of the extruded Mg alloy sheet fabricated by Li addition was accomplished by the tilted weak basal texture. The microstructure evolution and properties were characterized and compared.

マグネシウム合金板の常温成形性

マグネシウム合金板の常温成形性

Numerical study of the effects of shear deformation and superimposed hydrostatic pressure on the formability of AZ31B sheet at room temperature

The effect of the shear deformation and the superimposed hydrostatic pressure on the formability of magnesium alloy sheet is simulated in terms of the forming limit diagram (FLD). The model employed is the elastic viscoplastic self-consistent (EVPSC) crystal plasticity model, which accounts for both slip and twinning systems as the deformation mechanisms. The conventional sheets have low formability at room temperature due to the strong basal texture developed by the rolling process. However differential speed rolling process develops relatively weak basal texture by introducing shear deformation. Therefore the formability of the sheets produced by differential speed rolling is enhanced. In terms of the superimposed hydrostatic pressure, it delays the onset of necking and therefore improves the formability of sheets. In addition, the effect of crystal elasticity on the formability of sheets is numerically studied.

Material sensitivity and formability prediction of warm-forming magnesium alloy sheets with experimental verification

This paper proposes a theoretical method for predicting the formability of magnesium alloy sheets at elevated temperatures by combining the Marciniak and Kuckzinsky model with the Logan–Hosford yield criterion. In addition, the material sensitivity under different strain rates from 0.001 to 0.1 s−1 and elevated temperatures on forming the magnesium alloy was also investigated in this study. Forming limit tests on AZ31B magnesium alloy sheets were performed concurrently for the theoretical forming limit diagram (FLD) verification using a self-developed forming facility at elevated temperatures of 200, 250, and 300 °C and, simultaneously, the material sensitivity effect under a selective strain rate of 0.01 s−1. Based on the verified FLD prediction results, numerical simulations of warm-forming a AZ31B camera casing of thickness 0.8 mm as an example were then carried out. The warm forming experiments for this camera casing, under the identical conditions, were also performed for verification. As a consequence, it was found that the effect of strain rate on the prediction of FLDs did have a significant influence with increasing temperatures. Furthermore, the results of numerical simulations showed a good agreement with those of the warm forming experiments at different elevated temperatures. The proposed theoretical method offers a relatively accurate prediction in warm-forming magnesium alloy sheets and should lead to a remarkable reduction of trials, at least in the sense of both time and cost benefits, before a large batch production. Such outcomes of the study are expected to be very helpful and contributive to professionals, engineers, and the magnesium alloy-related applications in industry.

Evolution of neutral layer and microstructure of AZ31B magnesium alloy sheet during bending

Due to the poor formability of magnesium alloy sheet, evolution of neutral layer and microstructure was investigated by V-bending at 423 K. The results show that the neutral axis shifts dramatically toward the tension region of the specimen during V-bending. This is different from that of the general metals, like aluminum, whose neutral layer shifts to the compression region. This effect is attributed to the tension–compression asymmetry between the outer and inner regions of the specimen during bending. Moreover, the enhancing tension–compression asymmetry induced by the inhomogeneous texture formed throughout the thickness of V-bended sheet is also a key factor in the shift of neutral layer.

Formability of AZ31 magnesium alloy sheets during magnetic pulse bulging

Electromagnetic forming (EMF), i.e., magnetic pulse forming, with and without an Al driver sheet is experimentally performed to investigate the formability of an AZ31 magnesium alloy sheet during high speed forming. The formability of the magnesium alloy AZ31 during EMF is compared with that during traditional quasi-static tests. The results show that the formability of the magnesium alloy sheet undergoing the EMF process without the driver sheet is increased compared with that during quasi-static tests. To improve the energy efficiency of and to accelerate the AZ31 sheet, an Al driver sheet was used. The energy efficiency increases from 0.2% (no driver) to 1.8% (with a 2mm driver sheet). The forming limits of the magnesium alloy samples with the 2mm driver sheet are dramatically higher than those during quasi-static tests. The major and minor principal strains with the 2mm Al driver sheet increase by approximately 148% and 184%. The forming limits with 0.5 and 1mm driver sheets are similar to those during the EMF process without the driver sheet, enabling the AZ31 sheet to be formed at a higher strain. Increases in the major and minor principal strains with the 0.5mm driver sheet of approximately 68% and 72%, respectively, are achieved. According to the analysis of the crack fracture observations of the samples with the driver sheets, the fracture surfaces have obvious plastic dimples, which exhibit typical ductile rupture. The test results indicate that the formability could be significantly improved. The EMF process could be used in the manufacturing of AZ31 magnesium alloy sheet parts at room temperature.

Study on Mould Structure of Differential Temperature Drawing Process for Magnesium Alloy

Magnesium alloy, differential temperature drawing, mould structure, surface roughness Abstract. To improve the formability of magnesium alloy sheet, the differential temperature drawing process was presented, and the mould structure of differential temperature drawing process for magnesium alloy was well-designed and fabricated by analyzing the friction and the stress distribution of material in drawing process. With the blank heated to 200-235°C at the flange by inserting heating coils and thermocouples in die and binder and the drawn cup cooled by injecting cooling water into die and punch, the differential temperature drawing process of magnesium alloy sheet was performed successfully and the value of surface roughness Ra1.6um was adopted for punch, Ra0.4um was adopted for die and binder. The result shows that by using the designed mould, the deep drawing performance of AZ31B magnesium alloy can be enhanced obviously and the value of LDR can be increased form 2.1 to 3.05.

Formability of AZ31B Magnesium Alloy Sheet in Hydro-Bugling by Pulsating Hydraulic Pressure

The formability of the magnesium alloy sheets is poor at room temperature even though the magnesium alloy sheets are attractive because of their excellent characteristics. Hydro-forming technology, especially the pulsating hydro-forming, may be a way to improve the formability. Finite element simulations have been conducted to investigate the formability of AZ31B magnesium alloy sheet in hydro-bugling by pulsating hydraulic pressure. The influence of linear pressure, pulsating pressure and pulsating frequency on the maximum bulging height and minimum wall thickness of the formed parts have been analyzed. The research results show that the formability of AZ31B magnesium alloy sheet can be improved dramatically by pulsating hydro-forming. And enough bugling height can be obtained by lesser forming hydraulic pressure. The AZ31B sheet has an excellent performance in formability when the pulsating frequency is properly selected.