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.     

Cold stamping formability of AZ31B magnesium alloy sheet undergoing repeated unidirectional bending process

The repeated unidirectional bending (RUB) process was carried out on an AZ31B magnesium alloy in order to investigate its effects on the cold stamping formability. The limiting drawing ratio (LDR) of the RUB processed magnesium alloy sheet with an inclination of basal pole in the rolling direction can reach 1.5 at room temperature. It was also confirmed that cell phone housings can be stamped successfully in crank press using the RUB processed AZ31B magnesium alloy sheet. The improvement of the stamping formability at room temperature can be attributed to the texture modifications, which led to a lower yield strength, a larger fracture elongation, a smaller Lankford value (r-value) and a larger strain hardening exponent (n-value).     

Formability of AZ31 magnesium alloy sheets at warm working conditions

Fine-grained AZ31 magnesium alloy sheets were prepared through hot-rolling process. To investigate the mechanical properties of the sheets, uniaxial tensile tests were conducted at various temperatures and strain rates. The formability of AZ31 alloy sheets at warm working conditions was evaluated by limit drawing ratio (LDR) tests and limit dome height (LDH) tests at temperatures from 50 to 240 °C. It is demonstrated that LDR increases remarkably with temperatures, whilst LDH does not seem to increase much with temperatures. The maximum LDR reaches 2.65 at a punch speed of 30mm/min at 200 °C, whereas the maximum LDH is only 10.8 mm, showing good deep drawability and poor stretchability of AZ31 alloy sheets. In addition, punch speeds and punch temperatures were found to have significant effects on the deep drawability of AZ31 magnesium alloy sheets.     

����AZ31þ�Ͻ𱡰����³�������

针对AZ31镁合金板材室温冲压成形较差的特点,采用在不同轧制温度下获得的镁合金板材对其进行拉伸、埃里克森和锥杯试验,并通过光学电镜和X射线衍射仪对其显微组织、织构和成形性能等进行研究.结果表明,AZ31镁合金板材的综合力学性能不仅与晶粒尺寸有关,还与晶粒取向有关;基面织构的减弱可明显提高板材的胀形性能,在基面织构强度相似的强况下,晶粒大小对板材的成形性能起决定性影响.     

Improvement of formability of Mg–Al–Zn alloy sheet at low temperatures using differential speed rolling

The differential speed rolling (DSR) with a roll speed ratio of 1.167 was carried out on an AZ31B magnesium alloy in order to investigate its effects on the formability. Compared with the normal rolled sheet exhibiting approximately the same average grain size, the Erichsen values of the DSR processed sheet with an inclination of basal pole in the rolling direction significantly increased by about 1.5 and 1.9 times at room temperature and at 423 K, respectively. The deep-drawing temperature limit for a drawing ratio of 1.5 was also lowered from 443 K to 423 K. The improvement of the press formability at low temperatures can be attributed to the texture modifications, which led to a lower 0.2% proof stress, a larger uniform elongation, a smaller Lankford value and a larger strain hardening exponent.     

Deep drawing of square cups with magnesium alloy AZ31 sheets

The square cup drawing of magnesium alloy AZ31 (aluminum 3%, zinc 1%) sheets was studied by both the experimental approach and the finite element analysis. The mechanical properties of AZ31 sheets at various forming temperatures were first obtained from the tensile tests and the forming limit tests. The test results indicate that AZ31 sheets exhibit poor formability at room temperature, but the formability could be improved significantly at elevated temperatures up to 200 °C. The test results were then employed in the finite element simulations to investigate the effects of process parameters, such as punch and die corner radii, and forming temperature, on the formability of square cup drawing with AZ31 sheets. In order to validate the finite element analysis, the deep drawing of square cups of AZ31 sheets at elevated temperatures was also performed. The experimental data show a good agreement with the simulation results, and the optimal forming temperature, punch radius and die corner radius were then determined for the square cup drawing of AZ31 sheets.     

Improvement of stretch formability of Mg-3Al-1Zn alloy sheet by high temperature rolling at finishing pass

The effects of increasing rolling temperature from 723 K to 828 K at the last rolling pass on microstructure, texture, mechanical properties and stretch formability of a Mg-3Al-1Zn magnesium alloy previously rolled at 723 K were investigated. In the as-rolled condition, the basal texture strengthens slightly with increasing the rolling temperature whereas it weakens more remarkably after static recrystallization during annealing for the sheets rolled at higher temperatures. Only by increasing the rolling temperature from 723 K to 798 K, the Erichsen value is significantly increased from 4.5 to 8.6 due to the weakened texture for the annealed sheets. Further increasing the last rolling temperature does not appear to further improve the stretch formability.     

Effect of vertical rolling at various temperatures on subsequent multi-pass severe rolling of AZ31B alloy sheet

AZ31B alloy was subjected to vertical rolling at various temperatures prior to multi-pass severe rolling processing including initial rolling including one 80% reduction pass and finish rolling at 300 °C and 350 °C, respectively. The depth and number of edge crack, microstructure evolution and tensile properties were examined. The results indicate that pre-vertical rolling at low temperature before severe rolling can significantly restrain edge crack, change relative frequency distribution of edge-crack depth, increase microstructure homogeneity and sharply change the intensity and distribution of basal texture of initial-rolled sheets. The level of edge crack increases with increased vertical rolling temperature above 100 °C mostly due to the combination of shear band density, microstructure homogeneity, grain size and texture of rolled sheets. Compared with conventional rolling, the effect of vertical rolling on final mechanical properties depends on the finish rolling temperature due to the combination of shear bands, twins and grain size. The variation trend of mechanical properties with increased vertical rolling temperature is also sensitive to finish rolling temperature. For as-rolled sheets, the severe rolling route with vertical rolling at 100 °C and finish rolling at 300 °C should be required.     

轧制工艺对AZ31B镁合金薄板组织与性能的影响

研究了轧制温度和轧制速度对AZ31B镁合金薄板微观组织演变和力学性能的影响。结果表明,轧辊加热有利于镁合金薄板成型;AZ31B镁合金在低温或低速轧制时薄板纵向组织为大量的切变带,切变带区域包含大量孪晶组织,横向组织为含极少量孪晶的等轴晶组织;在轧制温度为400℃和轧制速度为16m/min轧制时,由于动态再结晶,横纵截面组织均为等轴晶。AZ31镁合金薄板的最佳轧制制度为轧辊温度为70℃、轧制温度为400℃、轧制速度为6m/min,此工艺轧制的薄板横向抗拉强度、屈服强度和伸长率分别为350MPa、300MPa和12%,纵向为345MPa、290MPa和11.2%,纵向与横向性能差别明显减小。     

AZ31B镁合金板液压-机械拉深试验研究

对AZ31B镁合金板进行液压-机械拉深试验,分析其变形特点和液压力对其成形性能的影响规律,并对液压拉深件的破裂现象进行了分析.试验结果表明,AZ31B镁合金板在液压-机械拉深时的成形性能比普通拉深时的差,主要原因是AZ31B镁合金板本身的塑性变形能力差,液压力未能及时发挥作用.     

Microstructure and mechanical properties of magnesium composites prepared by spark plasma sintering technology

Spark plasma sintering (SPS) technology was used to determine the appropriate conditions for SPS sintering of commercially pure magnesium as well as the magnesium alloy AZ31. It was found that the sintering temperatures of 585 °C and 552 °C were the most suitable sintering temperatures for the magnesium and the AZ31 alloy, respectively. Magnesium matrix and AZ31 alloy matrix composites reinforced with SiC particles were then successfully fabricated by the SPS method at sintering temperatures of 585 °C and 552 °C, respectively. A uniform distribution of SiC particles was observed along the boundary between matrix particles. The mechanical properties, i.e. hardness and tensile strength increased with increasing SiC content up to 10 wt%. However, when the SiC content was larger than 10 wt%, the tensile strength decreased due to the agglomeration of SiC particles. The agglomeration of SiC particles was found to lead to the degradation of the interfacial bonding strength between matrix and reinforcement.     

Effects of process parameters on warm and electromagnetic hybrid forming of magnesium alloy sheets

As the lightest structural metal, magnesium (Mg) is attracting increasing interest from both the industrial and academic fields. Magnesium alloy parts are mainly processed by die casting due to their poor sheet formability at room temperature. Warm forming is a popular method of forming; Mg alloy sheets produced in this manner show excellent formability around 200-400 °C. Electromagnetic forming (EMF) can improve the formability of metal sheets without the need for lubricants. In this paper, a new approach, called warm and electromagnetic hybrid forming (WEMF), is presented. The effects of voltage, capacity, and temperature on the bulging height of Mg alloy sheets are investigated. Results show that the bulging height of Mg sheets increases with moderate discharging energies. Enhancing the discharging voltage is also a more efficient method for increasing bulging height compared to simply increasing the capacity. When the discharging energy is kept constant, the bulging height first decreases (<150 °C) and then increases (>150 °C) from room temperature to 230 °C. The formability of Mg alloy sheets improves with increasing temperature, while the forming efficiency of WEMF decreases under similar conditions.     

Tensile properties and microstructure of AZ31B magnesium alloy sheet processed by repeated unidirectional bending

The mechanical properties of the AZ31B magnesium alloy sheet processed by repeated unidirectional bending (RUB) with a basal pole tilted in the rolling direction were systematically investigated at different temperatures. Compared with the as-received sheet exhibiting approximately the same average grain size, the fracture elongation increased while the proof stress decreased at room temperature. The initial texture had a significant influence on the mechanical properties at room temperature, while it showe...     

Cold Deep Drawing of Commercial Magnesium Alloy Sheets

A cold deep drawing process for commercial AZ31 magnesium alloy sheets was developed. The commercial sheets were successfully formed into circular cups at room temperature by optimising the annealing temperature of the sheets, i.e. a limiting drawing ratio of 1.75 was attained for an annealing temperature of 500 °C. The increases in elongation, n-value and r-value, and the decrease in flow stress effective in the improvement of drawability were obtained for the annealing. The apparatus for cold deep drawing without heating becomes much simpler than that for the conventional warm deep drawing. The effects of the lubricant, the clearance between the die and the punch and the corner radius of the punch on the drawability were examined. The limiting drawing ratio was increased by applying force onto the edge of a blank through the die corner. In addition, cold deep drawing of magnesium alloy square cups was performed. It was found that comparatively shallow magnesium alloy cups are satisfactorily formed at room temperature without heating.     

Microstructure and Mechanical Properties of Mg–3Al–Zn Magnesium Alloy Sheet by Hot Shear Spinning

Hot shear spinning experiments with Mg–3.0 Al–1.0 Zn–0.5 Mn(AZ31 B, wt%) magnesium alloy sheets were conducted at various temperatures, spindle speeds and feed ratios to investigate the effects of these processing parameters on the microstructure, crystallographic texture and mechanical properties. The AZ31 B sheet displayed good shear formability at temperatures from 473 to 673 K, spindle speeds from 300 to 600 rev/min and feed ratios from 0.1 to 0.5 mm/rev. During the dynamic recrystallization process, the grain size and texture were affected by the deformation temperature of the hot shear spinning process. Each of the spun sheets presented a strong basal texture, and the c-axis of most of the grains was parallel to the normal direction. The optimal hot shear spinning parameters were determined to be a temperature of 473 K, a spindle speed of 300 rev/min and a feed ratio of 0.1 mm/rev. The yield strength, ultimate tensile strength and elongation in the rolled direction reached 221 MPa, 288 MPa and 14.1%, and those in the transverse direction reached 205 MPa, 280 MPa and 12.4%, respectively. The improved strength and decreased mechanical anisotropy resulted from the fine grain size and strong basal texture.     

Mg sheet metal forming: Lessons learned from deep drawing Li and Y solid-solution alloys

The sheet formability of current magnesium alloys at ambient temperatures is poor; however, the formability at moderately elevated temperatures can be excellent. Cylindrical cup drawing tests are used to compare the warm forming characteristics of conventional alloy AZ31B with alloys containing lithium oryttrium solid solutions. While both types of experimental alloy can have better room-temperature ductility (ε_f∼25–30%) than AZ31B, only the lithium alloy has comparable or better deep-drawing capacity. The results are discussed in terms of the sheet anisotropy. Particular attention is drawn to the fact that magnesium alloys exhibit poor bending ductility due to their anisotropy and mechanical twinning-induced tension-compression strength asymmetry.     

Effect of Extrusion Strain Path on Microstructure and Properties of AZ31 Magnesium Alloy Sheet

The mechanical properties of AZ31 magnesium alloy sheets processed by different extrusion strain paths were examined in correlation with concurrent microstructure and texture evolution. The conventional extrusion(CE) and asymmetric extrusion(ASE) paths were performed on Mg alloy sheets. The textures at near surface and mid-layer of ASE sheets were various throughout sheet thickness direction as a result of extra asymmetric shear strain. This can stimulate the orientation of(0002) basal planes to incline approximately 12° toward the shear direction. Moreover, the basal texture of ASE sheet was weakened compared with CE one. Enhancing the ambient formability of extruded Mg alloy sheet fabricated by ASE path was accomplished by the tilted weak basal texture.     

Effect of pressurization profile on the deformation characteristics of fine-grained AZ31B Mg alloy sheet during gas blow forming

The deformation characteristics of a 0.6 mm-thick, fine-grained AZ31B Mg alloy sheet were investigated with the intention of reducing forming time during gas blow forming. The sheets were successfully deformed into hemispherical domes at 300, 370, and 420 °C under various pressurization profiles. The results show that the proposed pressurization profiles could achieve the goal of reducing forming time. A stepwise pressurization profile may be a suitable process at lower temperatures, whereas a constant or near constant pressure imposed during forming is a better method at higher temperatures. The pressurization profiles used in this study were not restricted to providing the optimum constant strain rate, which is often used in the traditional superplastic forming. Under the proposed pressurization profiles, maximum stress in the range of 23.5–45.6 MPa and resultant average strain rate in the range of 6.63 × 10⁻³ to 1.56 × 10⁻² s⁻¹ were imposed on the deforming sheet at the apex of the dome. The pressurization profile might not be one of the major factors influencing formability at the same forming temperature but it can significantly affect the forming time. Deviation of the bulged shape from the perfect sphere shape increased with increasing forming temperature.     

An Experiment on Magnetic Pulse Uniaxial Tension of AZ31 Magnesium Alloy Sheet at Room Temperature

Formability of magnesium alloys at room temperature or slightly elevated temperatures is low, and exhibiting poor resistance to strain localization and failure. However, it is possible to improve the formability of AZ31 magnesium alloy sheet at high strain rate such as by electromagnetic forming (or magnetic pulse forming). In this study, experimental investigation of uniaxial tension of AZ31 sheet by magnetic pulse forming at room temperature was presented. The approximate rectangular flat spiral coil was employed to carry out the experiments. The specimens used in the tension test by magnetic pulse forming were same as the quasi-static uniaxial test. The samples were placed close to the outside of coil where an approximately homogenous magnetic field distribution prevailed. The experimental results indicate that the total elongation of AZ31 sheet improves about 37% compared with the quasi-static case. Non-uniform deformation occurs in the specimen. The maximum strain takes place on the area C, where is plotted on the specimen. The major and minor principal strains at most increase by approximately 112 and 96% under 5.12 kJ energy. The experimental results obtained in this study provide the fundamentals for the investigation of high speed forming of AZ31 magnesium alloy sheets.     

Microstructure and mechanical properties of a basal textured AZ31 magnesium alloy cryorolled at liquid-nitrogen temperature

A strongly basal textured AZ31 magnesium alloy were cryorolled at liquid-nitrogen temperature at various strains. The microstructure and texture of the rolled sheets have been investigated using electron backscatter diffraction (EBSD) and X-ray diffraction. The microstructural and textural evolutions of the AZ31 magnesium alloy during cryorolling have been discussed. A lot of twins were observed in the rolled sheets. The influence of strain on the twin types and variant selection during cryorolling for the magnesium alloy has been discussed quantitatively based on the orientation data collected using EBSD. The influence of the twins on the microstructural and textural evolutions for the AZ31 magnesium alloy during cryorolling has also been discussed. The mechanical properties of the cryorolled sheets were tested by uniaxial tensile tests at the ambient temperature with a strain rate 10^-3s^-1 in the tensile direction respectively along the rolling and transverse directions of the rolled sheets. The relationships between the mechanical properties and microstructure of the cryorolled sheets have been discussed in the present work. The active twinning during rolling at that cryogenic temperature has been found to play an important role in influencing the microstructure, texture, as well as the mechanical properties of the AZ31 magnesium alloy.