Texture and stretch formability of rolled Mg-Zn-RE （Y, Ce, and Gd） alloys at room temperature

To develop a new magnesium alloy with excellent formability at room temperature, the effect of Y, Ce, and Gd addition on texture and stretch formability of Mg-1.5Zn alloys was carried out. The result shows that Y, Ce, and Gd addition in Mg-1.5Zn alloys can effectively weaken and modify the basal plane texture, characterized by TD-split texture in which the position of basal is titled from normal direction （ND） toward transverse direction （TD）. When Mg-1.5Zn alloy with Gd addition appears low texture intensity and TD-split texture, where the position of basal poles is tilted by about 4-35° from ND toward to TD, the largest Erichsen value of 7.0 and the elongation rate reaches 29.1% in TD direction. However, Y and Ce addition in Mg-1.5Zn alloys promote a large number of second phase particles, which cancel the contribution of the unique basal texture to stretch formability and ductility.     

Influence of initial texture on formability of AZ31B magnesium alloy sheets at different temperatures

Repeated unidirectional bending (RUB) process was carried out to improve the texture of AZ31B magnesium alloy sheets. Influence of initial texture on formability of AZ31B magnesium alloy sheets at different temperatures was investigated. Compared with the as-received sheets, the limiting drawing ratio of the RUB processed sheets increased to 1.3 at room temperature, 1.5 at 50 °C and 1.7 at 100 °C, respectively. The improvement of the press formability at lower temperatures can be attributed to the texture modification, which led to a smaller Lankford value and a larger strain hardening exponent. However, the press formability of the sheet with a weakened basal texture has no advantage at higher temperature. This is due to much smaller r-value that results in severe thinning in thickness direction during the stamping process which is unfavorable to forming. Anyhow it is likely that the texture control has more effect on the press formability at lower temperature.     

Twinning and texture evolution in binary Mg-Ca and Mg-Zn alloys

Texture evolution and formability in binary Mg-Ca and Mg-Zn alloys have been investigated in the present study. Static recrystallization during annealing treatment of rolled sheets leads to increase of basal pole intensity in Mg-3Zn alloy, but decrease in Mg-xCa alloys (x=0.05, 0.1 and 0.5). With increasing Ca content in Mg-xCa alloys, the basal texture becomes weaker, indicating that Ca is one of the effective elements in weakening the basal texture in Mg alloys. The effect of Ca on weakening the basal texture mainly comes from the presence of Ca atoms in the α-Mg solid solution matrix rather than from the Mg₂Ca particles formed during solidification. More frequent occurrence of compression (or double) twins results in weakening of the basal texture possibly due to lower stacking fault energy in Mg-Ca alloy than in Mg-Zn alloy. The room temperature formability of Mg-Ca alloy is highly superior to that of the Mg-Zn alloy.     

Enhanced mechanical properties and formability of hot-rolled Mg–Zn–Mn alloy by Ca and Sm alloying

In order to broaden the application of wrought Mg alloy sheets in the automotive industry, the influence of Ca and Sm alloying on the texture evolution, mechanical properties, and formability of a hot-rolled Mg–2Zn–0.2Mn alloy was investigated by OM, XRD, SEM, EBSD, tensile tests, and Erichsen test. The results showed that the average grain size and basal texture intensity of Mg–2Zn–0.2Mn alloys were remarkably decreased after Ca and Sm additions. 0.64 wt.% Ca or 0.48 wt.% Sm addition significantly increased the tensile strength, ductility and formability. Moreover, the synergetic addition of Sm and Ca improved the ductility and formability of Mg–2Zn–0.2Mn alloy, which was due to the change of Ca distribution and further reduction of the size of Ca-containing particles by Sm addition. The results provided a possibility of replacing RE elements with Ca and Sm in Mg alloys which bring about outstanding mechanical properties and formability.     

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).     

Forming limit diagram of auto-body steel sheets for high-speed sheet metal forming

This paper is concerned with the uniaxial tensile properties and formability of steel sheets in relation to the strain rate effect. The elongation at fracture for CQ increases at a high strain rate while the elongation at fracture for DP590 decreases slightly in relation to the corresponding value for a quasi-static strain rate. The uniform elongation and the strain hardening coefficient decrease gradually when the strain rate increases. The r-value of CQ and DP590 was measured with a high-speed camera in relation to the strain rate. The r-value is slightly sensitive to the strain rate. Static forming limit curves (FLCs) and high-speed FLCs were constructed with the aid of punch-stretch tests with arc-shaped and square-shaped specimens. In addition, a high-speed crash testing machine with a specially designed high-speed forming jig was used for the high-speed punch-stretch tests. Compared with the static FLC, the high-speed FLC of CQ is higher in a simple tension region and lower in a biaxial stretch forming region. The high-speed FLC for DP590 decreases in relation to the static FLC throughout the entire region. The elongation at fracture appears to be closely related to the simple tension region of the FLC. The shear fracture is observed from SEM images of specimens tested in the biaxial stretch forming region under the high-speed forming condition. The dimples indicating the shear fracture have elongated horseshoe shape. The high-speed FLC is lower than the static FLC in the biaxial stretch forming region because the shear fracture induces the decrease of ductility. The results confirm that the strain rate has a noticeably influence on the formability of steel sheets. Thus, the forming limit diagram of high-speed tests should be considered in the design of high-speed sheet metal forming processes.     

不同Gd含量对变形Mg-Zn-Gd合金织构和室温成形性能的影响

采用气氛保护加机械搅拌方法熔炼Mg-xZn-Ca-yHA (x=1,3,5;y=0,1,3,5)系列合金及其复合材料.通过金相显微镜(OM)和场发射扫描电子显微镜(FESEM)观察其铸态微观组织;X-射线衍射仪(XRD)分析物相组成;电化学和体外浸泡实验测试挤压态复合材料的耐腐蚀性能.结果表明,纳米羟基磷灰石(HA)颗粒可添加至Mg-Zn-Ca合金中,并在冶炼温度下脱水,转变成为了β-Ca3(PO4)2,同时显著细化基体合金的晶粒.其中,添加质量分数1％HA的复合材料具有最好的耐腐蚀性能.Mg-3Zn-Ca/1HA复合材料的腐蚀电位、腐蚀电流密度和腐蚀速率分别为-1.582 V,1.47μA/cm和14.19 mm/a,明显优于Mg-3Zn-Ca合金的-1.662 V,2.22μA/cm和21.28 mm/a.而添加3％HA的Mg-3Zn-Ca-3HA复合材料由于HA在基体中的部分团聚导致其耐腐蚀性能较Mg-3Zn-Ca合金有所下降.     

Excellent room-temperature ductility and formability of rolled Mg-Gd-Zn alloy sheets

In order to develop new magnesium alloy sheets with high formability at room temperature, the microstructure, texture, ductility, and stretch formability of rolled Mg-2%Gd-1%Zn and Mg-3%Gd-1%Zn sheets were investigated. The microstructures of these rolled sheets consist of fine recrystallized grains with a large amount of homogeneously distributed tiny particles in the matrix. The basal plane texture intensity is quite low and the basal pole is tilted by about 30° from the normal direction toward both the rolling direction and the transverse direction. The sheets exhibit an excellent ultimate elongation of ∼50% and a uniform elongation greater than 30%, and the Erichsen values reach ∼8 at room temperature. The flow curves of the two Mg-Gd-Zn alloys sheets display a remarkable linear hardening after an obvious yield point. The majority of the grains in the tilted texture have an orientation favorable for both basal slip and tensile twinning because of a high Schmid factor. The excellent stretch formability at room temperature can be attributed to the non-basal texture and low texture intensity, which led to the following characteristics: a lower 0.2% proof stress, a larger uniform elongation, a smaller Lankford value and a larger strain hardening exponent.     

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.     

Evolution of the plastic anisotropy with straining and its implication on formability for sheet metals

The plastic anisotropy r-value is an important material parameter in sheet metal forming. The length and width strains are measured conventionally in the uniaxial tensile test using two extensometers and the r-value is fitted within a certain strain range by linear regression according to the international standard. In this study, the physical character of the plastic anisotropy is analyzed for several forming steels and an aluminium alloy. In principle, the plastic anisotropy r-value is not a material constant. It is a fitted parameter within a given strain range and its value is dependent on the strain range chosen. More accurate approximation of the current state of anisotropy of a material is given by the incremental r-value that is defined in this study. Furthermore, this parameter can be predicted well by the VPSC code for materials in the as-received and deformed state. Contrary to previous studies elsewhere, the evolution of this incremental r-value does not correlate with anisotropic work hardening and the magnitude of the r-value. It is however closely related to texture evolution during plastic deformation. Texture evolution can have remarkable effect on the plastic anisotropy r-value, the yield locus and ultimately formability.     

Microstructures and Formability of the As-Rolled Mg-xZn-0.5Er Alloy Sheets at Room TemperatureEI北大核心CSCD

As lightweight requirements rise in transportation, aerospace, and other industries, magnesium alloys have a great application prospect. However, the low formability capabilities of magnesium alloys lead to a severe limit in applications. At present, there are many reports on the influences of texture and second phases on the formability of magnesium alloys at room temperature. Nevertheless, the dominant factors affecting the formability performance of magnesium alloys at room temperature are not clear. In this study, the development of the microstructures and texture of Mg-xZn-0.5Er (x = 0.5, 2.0, 3.0, 4.0, mass fraction, %) alloy sheets were studied, and the impact of the texture and second phases on the formability of these sheets were also investigated. The findings showed that the increase in Zn addition led to an early and complete dynamic recrystallization (DRX) in Mg-Zn-Er alloys sheets, and these recrystallized grains would expand significantly during subsequent hot rolling processes. These recrystallized grains with a large size were typically elongated and then helped to create a strong basal texture. Thus, it was discovered that the microstructures of these sheets were typically made up of equiaxed and elongated grains. The formability performance of these sheets was strongly related to the size of the second phases and the texture. The formability of the sheets containing microscopic second phases mainly depended on the basal texture, while the formability of the sheets which contained coarse second phases was mostly influenced by the second phases and basal texture. Particularly, when the component of the coarse second was larger, the formability would get more inferior due to the predominant role of the second phase at room temperature.     

Threshold tool-radius condition maximizing the formability in SPIF considering a variety of materials: Experimental and FE investigations

In the current study, a new level of understanding on the influence of using small tool radii on the formability (θ_max) is identified for single point incremental forming (SPIF). The relative value of tool radius and blank thickness (i.e., R/T_B, where R is the tool radius and T_B is the blank thickness) was varied over a range (from 1.1 to 3.9), and a formability diagram in the R/T_B–θ_max space was obtained. The formability was observed to show an inverse V-type pattern which revealed that there is a critical radius of tool (R_c) that maximizes the formability in SPIF. Further, this radius which was found to be independent of the material type (or property) is a function of blank thickness related as, R_c≈2.2T_B. This radius was termed as threshold radius. The formability, in agreement with general opinion in the literature, was noticed to increase with the decrease in the tool radius above the threshold value. However, contrarily it reduced with the decrease in the tool radius below the threshold value. In fact, undue surface cutting and metal squeezing was detected when the tests were performed with pointed tools, i.e., below threshold radius. This unstable deformation, which according to the FE analyses was found to be an outgrowth of in-plane compression under the tool center, increasingly weakened the material by inducing corresponding increase in damage (quantified by stress triaxiality) with the decrease in the tool radius. On the other hand, the damage was also observed to increase due to decrease in compression with the increase in the tool radius above the threshold value. This revealed high compression with low damage constitutes the most conducive condition that maximizes the formability in SPIF, which is realized when R≈2.2T_B.     

AZ31镁合金薄板经不同累积应变的连续弯曲变形后的显微组织与成形性能

对AZ31镁合金板材进行不同累积应变的连续弯曲变形及退火处理,随后对显微组织与力学性能的变化进行了研究。结果表明:经不同累积应变的连续弯曲变形后,镁合金板材的显微组织中没有发现孪晶,退火后,板材表层的晶粒异常长大,粗晶层的厚度随着累积应变的增加而增加,并且镁合金板材的织构朝RD方向偏转,偏转角度随累积应变的增加而增大;与原始板材相比,连续弯曲变形及退火处理使镁合金板材呈现出较好的室温成形性能(杯突值由2.3 mm提高到4.9 mm,提高了~113%),这主要归因于基面织构的改善使镁合金板材的r值减小与n值增大。     

The effect of texture and strain conditions on formability of cross-roll rolled AZ31 alloy

The effect of texture evolution of AZ31 Mg sheet on cross-roll rolling process has been investigated for the commercial AZ31 Mg sheet. The large ?₂₃ was operated for the cross-roll rolled sample throughout the whole thickness, leading to the homogeneity of the (0 0 0 2) basal texture. After recrystallization annealing at 673 K for 30 min, cross-roll rolled sample showed uniform texture intensity from surface layer to middle layer different from the normal-roll rolled sample. An excellent formability of the cross-rolled specimen was achieved due to the developed homogeneity of the texture and microstructure refinement for the cross-roll rolled specimen. The strain conditions of surface and center layers were discussed in terms of experimental evaluations and three-dimensional finite element method (FEM) for conventional rolling and cross-roll rolling.     

Effect of Ti addition on forming limit diagrams of Nb-bearing ferritic stainless steel

In order to better understand the grain size, texture evolution and forming limit major strain of ferritic stainless steel, two kinds of ultrapure ferritic stainless steels (Nb single stabilization and Nb + Ti dual stabilization) with 15 wt%Cr content of the same thickness processed by the same annealing treatment have been studied in this work. Ti addition does not improve the r-value as much, but it appears to refine the grain size of the ferrite and increase the {1 1 1}〈1 1 2〉 texture component in the γ-fiber, especially reduce the planer anisotropy value. The enhancement of the formabilities especially the drawability in forming limit diagram of Nb + Ti dual stabilization 15%Cr ferritic stainless steel mainly due to the refinement of the grain size, higher average r-value and lower planer anisotropy value.     

终轧温度对铁素体不锈钢织构和成形性的影响

在实验室研究了终轧温度对铁素体不锈钢显微组织、织构和成形性的影响。结果显示,随着终轧温度的降低(从940℃到800℃),冷轧退火板的组织细化,γ再结晶织构强度增加,平均塑性应变比r值增加,平面各向异性Δr值降低。终轧温度的降低显著改善了薄板的成形性能。     

Effect of <Emphasis Type="Italic">r</Emphasis>-value and texture on plastic deformation and necking behavior in interstitial-free steel sheets

Three initial tensile specimens having different textures and, in consequence, different r-values were cut from a sheet of an interstitial-free steel. Using these specimens, the effect of r-value and texture on plastic deformation and the necking behavior were studied by tackling the strain state and texture during tensile tests. A reduced decrease in work hardening rate of tensile specimens with higher r-values led to a slower onset of diffuse necking which offers an increased uniform elongation. A slower reduction in thickness of specimens with a higher r-value provided a favorable resistance against onset of failure by localized necking.     

Effects of aging on the microstructures and mechanical properties of extruded AM50 ＋ xCa magnesium alloys

The effects of aging treatment on the microstructures and mechanical properties of extruded AM50 ＋ xCa alloys （x=0, 1, 2 wt.%） were studied. The results indicated the secondary phase Mgl7Al12 precipitated from the saturated α-Mg solid solution while Al2Ca changed slightly when the aging time was increased. The hardness of extruded AM50 ＋ xCa al- loys increased initially to its peak, and then dropped to reach its original hardness with the increase in aging time. With the increase in aging temperature, the hardness of the AM50 ＋ 2Ca ahoy decreased, whereas the hardness of AM50 and AM50 ＋ 1Ca alloys decreased in the initial stages of aging treatment and increased in the later stages of aging treatment. The tensile strengths of AM50 and AM50 ＋ 1Ca alloys increased after aging treatment for the precipitation of Mg17Al12 phase, which increases the resistance against dislocation movement at the grain boundary; with increase in aging temperature, their tensile strengths increased. For AM50 ＋ 2Ca alloy, the tensile strength declined after aging at 150℃ and 175℃, while it increased slightly at 200℃. The ductility of AM50 ＋ xCa alloys （x = 0, 1, 2 wt.%） declined after aging treatment.     

Effect of coating characteristics on friction and formability of Zn-Fe alloy electroplated sheet steel

The effects of coating composition and coating weight on friction characteristics and formability under different deformation modes, as well as their mechanisms, were studied on zinc-iron electroplated drawing-quality special-killed (DQSK) sheet steels. Friction tests, simulative formability tests, and coating characterization were performed. The experiments revealed that the iron concentration of the coating has a tremendous effect on friction in the deep-drawing operation, but only a slight effect in the stretching operation. Uniaxial tension tests indicated that both coating weight and coating composition affectn-value andr-value. The dependence of friction characteristics,n-value, andr-value on iron concentration is related to the variation of coating hardness caused by the variation of iron concentration in the coating.     

Self-propagating high-temperature synthesis of (Zr,W)C/WC/Al2O3 composite powders from WO3-ZrO2-Al-C system

In the present study, the self-propagating high-temperature synthesis of 2(1-x)WO₃-3xZrO₂-Al-2(1 + 0.5x)C system was considered to prepare WC-ZrC-Al₂O₃ composite powders. The effects of an increase in the x-value between 0 and 1 as well as the addition of 50 wt% extra carbon to the initial reactant mixture on the adiabatic temperature, reaction front velocity, structure and microstructure of the combustion products were investigated. Results showed that the adiabatic temperature and the reaction front velocity decreased with increasing the x-value until it reached zero for x = 0.5. For x = 0 sample, WC, W₂C and W phases were formed after the synthesis process. The addition of extra carbon led to an increase in the (WC + W₂C)/W ratio. Furthermore, (Zr,W)C/WC/W₂C/Al₂O₃ composite powders were obtained for x > 0. Moreover, the (Zr,W)C concentration with near-stoichiometric composition and blocky morphology increased with the x-value. Differential thermal analysis results illustrated that the SHS reaction in the WO₃-ZrO₂-Al-C system is initiated by the aluminothermic reaction of WO₃. Moreover, it was postulated that the presence of W facilitated the formation of zirconium carbide.