Influence of microstructure and texture on formability of AZ31B magnesium alloy sheets

The effect of the repeated unidirectional bending （RUB） process and annealing on the formability of magnesium alloy sheets was investigated. The RUB process and annealing treatments produce two effects on microstructure： grain coarsening and weakening of the texture. The sheet that underwent RUB and was annealed at 300 ℃exhibits the best formability owing to the reduction of the （0002） basal texture intensity, which results in low yield strength, large fracture elongation, small Lankford value （r-value） and large strain hardening exponent （n-value）. Compared with the as-received sheet, the coarse-grain sheet produced by RUB and annealing at 400 ℃ exhibits lower tensile properties but higher formability. The phenomenon is because the deformation twin enhanced by grain coarsening can accommodate the strain of thickness.

Textural Evolution of AZ31B Magnesium Alloy Sheets Undergoing Repeated Unidirectional Bending at Room Temperature

In this paper, repeated unidirectional bending （RUB）, was applied to improve the texture of AZ31B magnesium alloy sheets so as to enhance their stamping properties. The samples undergoing RUB were annealed at different temperatures. The mechanical properties, formability, textural components and microstructure of the samples before and after RUB were characterized and compared. It was found that the basal textural component was reduced dramatically by RUB, and that （1212） and （1211） textural components appeared. Annealing has a great effect on the mechanical properties of samples undergoing RUB. The plasticity and stamping formability of samples were greatly improved by RUB and annealing at 260℃ for 1 h, and elongation to fracture and Erichsen value were increased to 38% and 67%, respectively.

Structure and properties of AZ31B magnesium alloy sheets processed by repeatedly unidirectional bending at different temperatures

Repeatedly unidirectional bending(RUB) was applied to the magnesium alloy sheet to improve the basal texture.The effect of RUB temperature on resulting structure and room temperature properties was investigated.The texture components of the sheet undergoing RUB at recovery temperature were similar to those of the sheet undergoing RUB at room temperature(RT).As the RUB temperature increased to above recrystallization temperature,the texture components became more disperse and the pyramidal components increased.With the increase of RUB temperature,the grain size near the surface of the sheets undergoing RUB tended to grow up.When the sheets were processed by RUB at medium-high temperature followed by annealing at 533 K,the yield strength and fracture elongation were lower than those of the cold rolled sheet;however,the Erichsen value was slightly higher than that of the cold rolled sheet.The sheet undergoing RUB at RT followed by annealing at 533 K represented the best mechanical properties.

Forming limit of textured AZ31B magnesium alloy sheet at different temperatures

Repeated unidirectional bending （RUB） was carried out to improve the texture of commercial AZ31B magnesium alloy sheets. All specimens were prepared in the rolling direction. The forming limit diagrams （FLDs） of AZ31B magnesium alloy sheet were determined experimentally by conducting stretch-forming tests at room temperature, 100, 200 and 300 ℃ Compared with the as-received sheet, the lowest limited strain of AZ31B magnesium alloy sheet with tilted texture in the FLD increased by 79% at room temperature and 104% at 100 ℃. The texture also affected the extension of the forming limit curves （FLC） in the FLD. However, the FLCs of two kinds of sheets almost overlapped at temperature above 200 ℃. It can be concluded that the reduction of （0002） texture intensity is effective to the improvement of formability not only at room temperature but also at low-and-medium temperature. The effect of texture on FLDs becomes weak with increasing temperature.

Electroplastic effect in AZ31B magnesium alloy sheet through uniaxial tensile tests

The electroplastic effect in AZ31B magnesium alloy sheet was investigated through uniaxial tensile tests. In order to show the athermal effect of the electrical pulses, two types of uniaxial tensile tests at the same testing temperature were carried out： uniaxial tension in environmental cabinet and uniaxial tension with electrical pulses. In addition, the distribution of temperature field in the cross-section area during uniaxial tension with electrical pulses was simulated. The results show that the distribution of temperature field along the cross-section area is homogeneous. By comparing the true stress？true strain curves of AZ31B alloy under uniaxial tensile tests, the athermal effect with electrical pulses was confirmed. The microstructure evolution after the uniaxial tension was studied by optical microscopy. The results indicate that the electrical pulses induced dynamic recrystallization plays an important role in the decrease of flow stress. Finally, a flow stress model of AZ31B sheet taking the influence of electroplastic effect into account was proposed and validated. The results demonstrate that the calculated data fit the experimental data well.

Flexible die drawing of magnesium alloy sheet by superimposing ultrasonic vibration

Combining solid granule medium forming technology with ultrasonic vibration plastic forming technology, ultrasonic vibration granule medium forming （UGMF） technology was proposed. To reveal the effect of ultrasonic vibration on flexible-die deep drawing, an ultrasonic vibration with a frequency of 20 kHz and a maximum output of 1.5 kW was on the solid granule medium deep drawing of AZ31B magnesium alloy sheet. The results revealed that ultrasonic vibration promotes the pressure transmission performance of the granule medium and the formability of the sheet. The forming load declines with the ultrasonic amplitude during the drawing process as a result of the combined influence of the ＂surface effect＂ and the ＂softening＂ of the ＂volume effect＂.

The Stamping Formability of AZ31 Magnesium Alloy Sheet Improved by Equal-channel Angular Pressing

Equal channel angular pressing （ECAP） processing and annealing were applied to the AZ31 magnesium alloy sheets to evaluate the potential improvement in the mechanical properties and formability. The ECAP experiment was conducted at 300 ℃ in a die having an included angle of 90o between two channels by the BCZ route with the sheets rotated by 90°about the normal axis of plate plane. The tensile tests and conical cup tests were conducted at various temperatures from 20 to 250 ℃. The experimental results indicated that improving the working temperatures could lead to the soft in the material and the enhancement of ductility. Comparatively, the ECAPed AZ31 alloy sheets showed the lower yield strength and smaller conical cup value （CCV） than the unECAPed counterpart in the room temperature. The difference in yield strength between them became small in the elevated temperature, but the ECAPed samples still had the smaller CCV value, implying the improved formability. The texture of the AZ31 alloy sheets could be modified by ECAP and the decrease in the yield strength and more uniform deformation realized in the material, so the formability of AZ31 alloy sheets was improved.

Effect of deformation mode,dynamic recrystallization and twinning on rolling texture evolution of AZ31 magnesium alloys

In order to obtain quantitative relationship between（0002） texture intensity and hot rolling conditions, conventional rolling experiments on AZ31 magnesium alloys were performed with 20%-40% reductions and temperatures within the range of 300-500 ℃. Shear strain and equivalent strain distributions along the thickness of the rolled sheets were calculated experimentally using embedded pin in a rolling sheet. Rolling microstructures and textures in the sheet surface and center layers of the AZ31 alloys were measured by optical microscopy（OM）, X-ray diffractometry（XRD） and electron back scatter diffraction（EBSD）. Effects of the rolling strain, dynamic recrystallization（DRX） and twinning on the texture evolution of the AZ31 alloys were investigated quantitatively. It is found that the highest（0002） basal texture intensities are obtained at a starting rolling temperature of 400 ℃ under the same strain. Strain–temperature dependency of the（0002） texture intensity of the AZ31 alloy is derived.

Optimisation of alloy composition for highly-formable magnesium sheet

The effectiveness of Ca or Gd addition on ductility and formability of Mg-Zn-Zr based dilute alloys in deep drawing has not been systematically compared previously.In this study,formable Mg-Zn-Gd-Zr and Mg-Zn-Ca-Zr sheet alloys are produced by hot rolling.These sheets have similarly weakened basal texture,but the sheet of the Mg-Zn-Gd-Zr alloys has higher ductility and formability than that of Mg-Zn-Ca-Zr alloys.The combined addition of 0.2wt%Ca and 0.4wt%Gd to the Mg-1Zn-0.5Zr(wt%)alloy leads to a Mg-1Zn-0.4Gd-0.2Ca-0.5Zr alloy that has even better ductility,and its formability during deep drawing is comparable to the benchmark Al6016 sheet.An increase in Ca content from 0.2wt%to 0.5wt%leads to decreased sheet ductility and formability,predominantly due to grain boundary embrittlement.

Microstructure characteristics and liquation behavior of fiber laser welded joints of Mg-5Zn-1Mn-0.6Sn alloy sheets

Fine-grained Mg?5Zn?1Mn?0.6Sn alloy sheets of2mm in thickness were welded by fiber laser welding.The appearanceand microstructures of the welding joints and liquation behaviors in the partially melted zone(PMZ)were investigated.The resultsshow that,with the lower welding power and higher welding speed,the width and depth of the joints decrease.Moreover,some poresare detected at a very high welding speed.There are two kinds of liquation phenomena in the PMZ.One is the liquation networkalong grain boundaries associated with the liquation of substrate and segregation-induced liquation,the other is the molten poolinvolved with the liquation of the residual second phases at the boundaries.However,the liquation of substrate and thesegregation-induced liquation are the main liquation mechanism in the PMZ.

Cold stamping for AZ31B magnesium alloy sheet of cell phone house

Electric product house of magnesium alloy sheet is usually obtained by warm stamping owing to its poor plasticity and formability at room temperature.The formability of AZ31B magnesium alloy sheet can be improved by repeated unidirectional bending(RUB)process through control of(0002)basal texture.Compared with as-received sheet,the Erichsen value(IE)of the sheet underwent RUB process increases to 5.90 from 3.53 at room temperature.It is also confirmed that cell phone houses could be stamped successfully in crank press with AZ31B magnesium alloy sheets underwent RUB process.It provides an alternative to the electronics industry in the application of magnesium alloys.

Hot tensile deformation behavior and constitutive model of ZK61M high-strength magnesium alloy sheet

Hot deformation behavior of the annealed ZK61 M magnesium alloy sheet was explored using tensile tests with strain rates varying from 0.001 to 0.030 s^(-1) in temperatures range of 423-513 K.The obtained results indicate that the flow stress increased with deformation temperature decreasing and strain rate increasing.Dynamic recrystallization(DRX)occurs when the temperature is higher than 423 K,and the recrystallization volume fraction increases with temperature rising.At a given temperature,the measured DRX volume fraction at a higher strain rate is smaller than that at a lower strain rate.Dimples are observed throughout the tested temperature range.Moreover,they grow larger as temperature increases.An average absolute relative error(AARE)of 2.65%proves that the peak stress predicted by the constitutive model is in good agreement with the experimental results.The correlation coefficient(R’)obtained for the predicted stress and the experimental value considering the strain on the material constant are between 0.9831 and 0.9977.In addition,AARE and root mean square error(RMSE)are less than 6.5%and 8.5 MPa,respectively.This indicates that the deviation of the predicted value from the experimental value is small and the predictions of the proposed model are reliable.

Thermal Flow Simulation of Twin-Roll Casting Magnesium Alloy

In order to better understand twin-roll casting process,a 3D finite element method(FEM) simulation was carried out,based on the conditions of the pilot vertical twin-roll caster,to study the thermal flow and solidification behavior in the twin-roll casting process.The simulation results show that non-uniform temperature and velocity distribution near the side dam region are the main reason for causing non-uniform solidification and non-uniform deformation along the cast sheet width.Therefore,it is necessary to preheat the side dams or improve the design of nozzle to compensate the effect of side dams on the casting process.High quality magnesium sheets have been cast after improved the casting devices.

Experimental Exploration of Electrical Pulse-Assisted Roller Hemming of AZ31B Magnesium Alloy Sheet

The purpose of this research is to explore the feasibility of roller hemming of AZ31 B magnesium alloy sheet. During the test, a special experimental setup considering the current flow and insulation was designed and employed. For the sake of simplicity, the flat surface-straight edge hemming style was selected. Electrical pulses were introduced in the pre-hemming and final hemming processes. The results show that when hemming at 448 K with hemming speed of 30 mm/min, AZ31 B magnesium alloy sheet was successfully hemmed with excellent perceived quality. No recoil/warp defect, cracking or springback was observed. Electrical pulses induced dynamic recrystallized grains were observed along the grain boundaries in the severely deformed area, which is of great importance to the improvement of the ductility of the material. The hardness was slightly increased after hemming with electrical pulses, and this fact could improve the friction resistance performance of the hemmed part.

Deformation Behavior and Microstructure Evolution of AZ31 Mg Alloy by Forging-Bending Repeated Deformation with Multi-pass Lowered Temperature

In this study, AZ31 Mg alloy was processed by a new severe plasticity deformation methodology with multi-pass lowered temperature, and the deformation behavior and microstructure evolution were investigated by finite element method and electron back-scattered diffraction technique and hardness. The results show that with the increase of deformation pass, the strain gradually springs, and its interval distribution tends to homogenize. Meanwhile, the effective strain increases dramatically with the shear force sudden upgrade in the deformation process. Moreover, the new deformation technique can refine grain size remarkably. With the passes on, {10-12} tensile twins behavior and the pyramidal < c + a > slip are triggered more frequently, leading to the completeness of dynamic recrystallization (DRX) gradually, which weaken and disperse the basal texture obviously. Besides, the standard deviation of hardness is getting smaller, and the maximum can reach 78.40 HV on average, which can be attributed to the even large strain distribution, complete DRX, and the high geometrically necessary dislocation.