Microstructure and formability evolutions of AZ31 magnesium alloy sheets undergoing continuous bending process

Continuous bending (CB) process along rolling direction was performed to improve the formability of AZ31 magnesium alloy sheets. The microstructure and texture evolutions were characterized by optical microscopy (OM) and electronic backscatter diffraction (EBSD). The results reveal that the basal texture intensity of continuously bent and annealed (CBA) sample is drastically weakened. A large number of twins are induced on the concave surface by the 1st pass bending and the density of twins obviously declines during the 2nd pass bending owing to the occurrence of detwinning. Due to the asymmetric tension?compression strain states between the outer and inner regions during V-bending, twinning and detwinning are generated alternatively during the CB process. The Erichsen value is 5.2 mm which increases by 41% compared with that of as-received sample. This obvious improvement of formability can be attributed to the weakened basal texture, which leads to a smaller plastic strain ratio (r-value)together with a larger strain-hardening exponent (n-value).

FEM Simulation of Bending Formability for Laminate Steel/Resin/Steel Lightweight Composite Sheet

The ANSYS simulation software was used to analyze the bending formability of laminate steel/resin/steel lightweight composite sheet. The skin steel at external side produces relative slipping-off change during the bending due to its composite structure. The internal stress strain states, materials effect tools parameters and intermediate layer resin of lightweight sheet on slipping-off change were analyzed. The spring back and shear stress state after bending have also been discussed.

Effect of bending and tension deformation on the texture evolution and stretch formability of Mg-Zn-RE-Zr alloy

Bending and tension deformations were performed on Mg-1.3 wt%Zn-0.2 wt%RE-0.3 wt%Zr(ZEK100)alloy sheets that initially had a transverse direction(TD)-split texture.The effects of bending and tension deformations on the texture formation and room-temperature formability of specimens were investigated.The specimen subjected to 3-pass bending and tension deformations exhibited an excellent Erichsen value of 9.6 mm.However,the Erichsen value deterioration was observed in the specimen subjected to 7-pass deformations.The rolling direction-split texture developed on the surface with an increasing pass number of deformations.Conversely,the clear TD-split texture remained at the central part.As a result,a quadrupole texture was macroscopically developed with an increasing pass number of deformations.The reduction in anisotropy by the formation of the quadrupole texture is suggested to be the main reason for the improvement in stretch formability.By contrast,the generation of coarse grains near the surface is suggested to be the direct cause for the deterioration of the stretch formability of the specimen subjected to 7-pass deformations.

Variations in microstructure and bending formability of extruded Mg–Al–Zn–Ca–Y–MM alloy with precompression and subsequent annealing treatment conditions

In this study, the bending formability of an extruded Mg–9Al–1Zn–0.3Mn–0.9Ca–0.6Y–0.5 MM(AZXWMM91100, wt%) alloy at room temperature is significantly improved through application of a combined precompression and subsequent annealing(PCA) treatment. As the amount of precompression applied along the extrusion direction(ED)(i.e., the total strain) increases from 4% to 6%, the area fraction of ED-oriented grains of the PCA-treated alloy increases, which consequently causes an improvement in its bending formability because these grains accommodate larger tensile strain along the ED during bending. As the temperature of the subsequent annealing treatment increases from 350 ℃ to 450 ℃, both the area fraction of the ED-oriented grains and the average grain size increase, and the residual dislocation density decreases owing to the promotion of boundary migration and occurrence of the recovery process at higher temperatures.Consequently, the bending formability of both the 4%-precompressed and the 6%-precompressed samples increases with an increase in the annealing temperature. However, when the precompressed samples are annealed at 300 ℃, their bending formability is lower than that of the extruded alloy because the dislocations formed by precompression remain even after the subsequent annealing at this temperature.

Weld Characteristics and NC Bending Formability of QSTE340 Welded Tube

The mechanical characteristics of the weld joint were investigated by tensile test, microstructure test, and microhardness test. The welded tube NC bending tests were carried out to evaluate the weld on the formability of the QSTE340 welded tube. The results show that the wall thinning degree, cross-sectional deformation and springback angle increase significantly as the weld line is located on the outside of the bend compared with that located on the middle and inside, and the welded tubes produce nearly identical performance as the weld line is located on the middle and inside. The wall thickening degree decreases much as the weld line is located on the inside of the bend. So the welded tube can acquire good bending formability as the weld line is located in the region away from the outside of the bend.

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.

Precision bending of high-quality components for volume applications

Recent new technology developments were presented in the field of industrial bending operations,including flexible stretch forming and 3D rotary stretch forming.Attempts were made to give an overview of different mechanisms that influence dimensional accuracy,including local cross-sectional deformations such as suck-in and volume conservation effects,along with global deformations such as springback.An analytical model was developed to determine the particular influence of different material,geometry and process parameters on dimensional variability of bent components.The results were discussed in terms of overall process capability(Cp) and associated process windows.The results show that different governing mechanisms prevail in various bending operations,meaning that attention has to be placed on controlling those process parameters that really are important to part quality in each specific case.Several strategies may be defined for reducing variability.One alternative may be to design more robust process and tool technology that reduce the effect of upstream parameters on dimensional variability of the formed part.The results show that optimal tool design and technology may in specific cases improve the dimensional accuracy of a formed part.Based on the findings discussed herein,it is concluded that advances in industrial bending operations require focus on improving the understanding of mechanical mechanisms,including models and parameter development,new technology developments,including process,tool,measurement and control capabilities,and process discipline at the shop floor,combined with a basic philosophy of controlling process parameters rather than part attributes.

Bending properties of extruded AZ91–0.9Ca–0.6Y alloy and their improvement through precompression and annealing

In this study,an extruded Mg–9Al–1Zn–0.3Mn–0.9Ca–0.6Y(AZXW9110)alloy is subjected to precompression and subsequent annealing(PCA)treatment for improving its bending formability,and the three-point bending properties of the as-extruded material and the precompressed and subsequently annealed(PCAed)material at room temperature are compared.During bending,microcracks formed in undissolved Al2Ca,Al2Y,and Al8Mn4Y particles propagate along the grain boundaries or twin boundaries and consequently form a macrocrack in the tension zones of the bending samples of both the materials.However,the bending formability of the PCAed material is 75%higher than that of the as-extruded material owing to the promoted twinning and slip behaviors in the former.The as-extruded material has a strong normal direction(ND)texture and a weak transverse direction(TD)texture,and the ND-and TD-oriented grains are unfavorable for both{10–12}twinning and basal slip in the tension zone of the bending sample of this material,which eventually results in its low bending formability.The PCAed material has a strong extrusion direction(ED)texture,weak TD texture,and spread ND texture.During bending,{10–12}twins are fully formed in the ED-oriented grains,and this{10–12}twinning effectively accommodates the plastic strain in the tension zone.In addition,the activation of basal slip in the ND-oriented grains of the PCAed material is promoted owing to the spread ND texture of this material.Consequently,this material exhibits substantially superior bending formability because of the vigorous{10–12}twinning in its ED-oriented grains and promoted basal slip in its ND-oriented grains.

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.

Ti−6Al−4V合金板材在电脉冲辅助弯曲过程中的显微组织演变及成形性能

在有效电流密度为0~3.2 A/mm^(2)、占空比为10%~70%条件下对Ti−6Al−4V合金板材进行电脉冲辅助弯曲实验。结果表明:当有效电流密度从0增加到2.4 A/mm^(2)时,弯曲成形位移从9.15 mm增加到15.60 mm;同时,裂纹的尺寸和宽度减小。此外,当弯曲位移为8 mm时,回弹角随着有效电流密度的增加而减小。占空比同样影响弯曲角,在30%占空比条件下能获得最小的弯曲角135.0°。板材的热稳定温度随着有效电流密度的增加而增加,但是与占空比呈非线性关系。此外,在电脉冲辅助弯曲过程中出现了晶粒粗化、{0001}织构强度增加和亚晶粒发展。电脉冲使位错密度降低且加速位错的重排,促进α晶粒内亚晶粒的形成,从而改善合金的成形性。电脉冲的非热效应提高了Ti−6Al−4V合金板材的低温成形性,使其与高温下的成形效果类似。

高强TA18钛管微观织构对拉伸力学性能与弯曲成形性能影响研究

目的揭示高强钛管微观织构强度与宏观各向异性指标CSR值的定量关系,阐明微观织构对钛管拉伸力学性能与弯曲成形性能的影响,为高强钛管冷轧微观织构及性能精确调控奠定重要基础。方法选取不同轧制工艺条件下获得的高强钛管进行单向拉伸测试及EBSD表征,分析微观织构对管材拉伸力学性能的影响;选取具有典型微观织构分布状态和CSR值的高强钛管进行数控绕弯试验及成形质量测试。结果单向拉伸力学性能测试结果表明,当CSR值为0.65~2.43时,随着CSR值的增大,颈缩阶段管材的应变与整体伸长率不断增大;数控绕弯试验结果表明,当高强钛管CSR值从1.27提高到1.48时,其断裂前最大弯曲角度从20°提高到110°,当CSR值增大到1.71时,可以成功实现120°的弯曲,并且随着CSR值进一步增大到2.14,弯管件的截面畸变率和壁厚减薄率不断减小。结论建立了可以准确描述宏观CSR与微观织构强度指标之间定量关系的双曲函数表达式,高强钛管径向织构强度的增强会提升高强钛管变形过程中抗壁厚减薄的能力,并有利于管材弯曲成形质量的提升。

弯曲参数对304不锈钢管材大曲率无芯弯曲成形性的影响

针对管材无芯弯曲多缺陷耦合的成形问题,以管材壁厚变化率及截面短轴变化率作为成形指标,在不同弯曲参数下进行304不锈钢管材大曲率无芯弯曲试验,结合硬度测试及微观组织表征,研究了弯曲参数对弯曲成形及微观组织演变的影响规律。结果表明:随着弯曲速度、弯曲角度及相对管径的增大,壁厚变化率呈增加趋势,且壁厚增厚率始终大于壁厚减薄率,同时,弯管截面畸变程度加剧。在各弯曲参数下,管材弯曲内外侧均发生奥氏体向马氏体转变,马氏体组织含量及硬度与壁厚变化率呈正相关关系,中性层几乎不存在马氏体。通过选择合适的工艺,最终弯制出相对弯曲半径为1.4的合格弯管。

V含量对汽车用碰撞件材料组织性能的影响

采用光学显微镜、扫描电子显微镜(SEM)、能谱仪(EDS)、电子万能试验机等测试分析手段,研究了V含量对汽车防撞梁型材组织、力学、折弯以及晶间腐蚀性能的影响。结果表明,随着V含量(质量分数)增加,晶粒尺寸先减后增,0.15%V时最小。力学性能测试显示,0.15%V时屈服强度和加工硬化指数n值增长最显著。自然时效后,0.15%V合金稳定性最佳;人工时效后,其强度增长最大,兼具良好成形性和时效强化性。折弯角度随V含量增加而增大,0.15%V时最大且TD、RD角度差值最小。四种合金均表现出晶间腐蚀,V含量变化对耐腐蚀性影响不明显。但V含量达0.20%时,折弯角度下降,归因于Al_(11)V相的形成。

Texture tailoring and bendability improvement of rolled AZ31 alloy using {10-12} twinning: The effect of precompression levels

In this study,the texture of a rolled Mg alloy is effectively modified through the application of precompression and subsequent annealing treatment,leading to a remarkable improvement in the bending formability of the alloy at room temperature.Precompression induces lattice reorientation through{10-12}twinning,and annealing treatment reduces the stored strain energy of the precompressed material,which results in the formation of a stable grain structure with two dominant texture components.With an increase in precompression,the tensile strain in the outer region of the bending samples is accommodated to a greater extent due to more pronounced{10-12}twinning and basal slip.As a result,the bending formability of the material at room temperature improves with greater precompression.The variation in microstructure,texture,and bending behavior in relation to the degree of precompression is discussed in detail.

Ni/Co质量比对Cu-Ni-Co-Si合金组织和性能的影响

采用SEM、XRD和力学性能等测试手段研究了Ni/Co质量比对Cu-Ni-Co-Si合金组织和性能的影响,尤其是通过研究织构对Ni/Co质量比与弯曲成形性能的关系进行了分析。结果表明:较小的Ni/Co质量比能够促进合金发生回复和再结晶转变,并且可以细化铸态和峰时效态合金的晶粒。在RD方向上,Ni/Co质量比为1时合金再结晶织构的取向密度最小,主要含有R{124}〈211〉和Copper{112}〈111〉织构。在TD方向上,Ni/Co质量比为1.5时合金再结晶织构的取向密度最小,主要含有Copper{112}〈111〉、S{123}〈634〉和R{124}〈211〉织构。此外,Ni/Co质量比为1时合金具有最高的硬度、电导率和伸长率以及相对高的强度。通过理论计算发现,Ni/Co质量比为1时合金在RD方向上最容易发生塑性变形。弯折试验结果表明,Ni/Co质量比为1时合金具有最好的纵向(GW)弯曲成形性能,最小弯曲比为2.1,试验结果与计算结果一致。

‘Size effect’ related bending formability of thin-walled aluminum alloy tube

Aluminum alloy （Al-alloy） thin-walled （D/t ＆gt; 20, diameter D, wall thickness t） bent tubes have attracted increasing applications in many industries with mass quantities and diverse specifications due to satisfying high strength to weigh ratio requirements of product manufacturing. However, due to nonlinear nature of bending with coupling effects of multiple factors, the similarity theory seems not applicable and there occurs a challenge for efficient and reliable evaluation of the bending formability of thin-walled tube with various bending specifications. Considering the unequal deformation and three major instabilities, the bending formability of thin-walled Al-alloy tube in changing tube sizes such as D and t are clarified via both the analytical and FE modeling/ simulations. The experiments of rotary draw bending are conducted to validate the theoretical models and further confirm ＇size effect＇ related bending formability. The major results show that （1） The anti-wrinkling capability of tube decreases with the larger D and smaller t, and the effect significance of t is larger than that of D even under rigid supports; （2） The wall thinning increases with the larger D and smaller t, and this tendency becomes much more obvious under rigid supports; （3） The cross-section deformation increases with the larger D and smaller t according to the analytical model obtained intrinsic relationship, while this tendency becomes opposite due to the nonlinear role of mandrel die; （4） The size factor D/t can be used as a nondimensional index to evaluate both the bending formability regarding the wall thinning and cross-section deformation.

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.

闭截面型材的拉弯成形性

拉弯是型材的基本成形方法.截面畸变是型材拉弯成形中的常见缺陷,并对型材的回弹和变薄有交叉影响,型材拉弯成形性的分析评估远比板材成形复杂.提出了型材拉弯成形性的概念,建立了矩形截面型材拉弯成形性分析模型,基于有限元数值模拟研究了截面结构、相对高度和壁厚分布等几何参数对拉弯成形性的影响规律,从提高拉弯成形性出发提出了型材截面优化设计的原则.

型材拉弯成形性评估专家系统

型材拉弯成形性与材料性能、截面形式和尺寸以及工艺参数有关,拉弯成形性图可定量表示型材拉弯成形性与截面尺寸及工艺参数之间的关系.基于型材拉弯成形性图的概念,建立了型材拉弯专家系统;分析了系统的功能、结构以及实现模块,对系统的关键技术和解决方法进行了研究.该系统以数据库为基础,基于数据的推理和图形显示,采用面向对象的编程技术和模块化设计思想予以实现;并通过实例表明了系统的可靠性.该系统可满足企业在并行工程下质量控制的需要,为型材拉弯成形性图在工业中的推广应用、型材拉弯成形水平的提高以及型材拉弯工艺的广泛应用奠定了基础.

2E12铝合金板材成形性能试验研究

针对航空用高强度2E12铝合金,通过试验对T3态和退火态两种状态下的2E12铝合金板材,在室温条件下的力学性能、杯突及弯曲成形进行了研究。试验结果表明:与T3态相比,2E12铝合金板材退火态的抗拉强度、屈服强度及屈强比明显降低,延伸率变化不大;杯突IE值提高了12%,最小弯曲半径值降低了10%,说明2E12铝合金板材退火态较T3态有更好的成形性能。