Microstructure and mechanical properties of cryorolled AZ31 magnesium alloy sheets with different initial textures

AZ31 magnesium alloy sheets with different strong textures were cryorolled at the liquid-nitrogen temperature to the strain of 4% and 8%. The microstructure and texture of the rolled sheets were investigated via scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and X-ray diffraction (XRD). The mechanical properties of the sheets were tested through in-plane uniaxial tensile tests at ambient temperature. The tensile stress was exerted in the rolling direction (RD) and transverse directions (TD). The microstructural and textural evolutions of the alloy during cryorolling were investigated. Due to active twining during rolling, the initial texture significantly influenced the microstructural and textural evolutions of the rolled sheets. A {1012} extension twin was found as the dominated twin-type in the cryorolled samples. After cryogenic rolling, the ductility of the samples decreased while the strength increased. Twinning also played an important role in explaining the mechanical differences between the rolled samples with different initial textures. The samples were significantly strengthened by the high stored energy accumulated from cryorolling.     

铸态镁合金大压下轧制对组织和边裂的影响

主要研究了道次压下率和轧制道次数对AZ31B扁锭坯大压下轧制所制备板材边裂以及微观组织的影响.轧制工艺为350℃下两道次或四道次大压下轧制.金相观察、边裂统计和XRD织构分析表明:当总压下率达到37%时,轧板开始出现边裂;并且裂纹深度随着压下率的增大而增加.随着压下率的增加,孪晶明显增多.当总压下率达到54%时,大部分区域已完成再结晶;进一步增大压下率,组织中出现变形局域化现象;当总压下率为82%,轧制道次增多时,边裂出现一定程度减弱,同时基面织构分布由双峰变为单峰.     

Mechanical behavior and microstructure evolution for extruded AZ31 sheet under side direction strain

AZ31 magnesium alloy sheets were prepared by a conventional extrusion (CE) and a novel integrated extrusion with side direction strain (SE). The microstructure characterizations, crystallographic texture and mechanical property tests were carried out and compared between the extruded Mg alloy sheets processed by CE and SE. The results indicated that the SE sheets exhibited an excellent combination of strength and ductility. To reveal the side strain effect, the finite element model was employed to investigate the effective stress and strain behavior of the AZ31 magnesium alloy sheets during CE and SE processes. It was found that the SE process was effective in weakening the stress and strain concentration. This implied that it developed an additional side direction strain through the sheet thickness during the hot extrusion. Meanwhile, the side strain shear paths could promote the local accumulation of dynamically recrystallized grains and increase the random high-angle boundaries to achieve weak (0002) basal texture. Important factors including the side strain path and extrusion parameters need to be taken into account to understand the deformation mechanism and microstructure evolution.     

多道次等径角轧制对AZ31镁板组织性能的影响

对AZ31镁合金进行多道次等径角轧制,并分析其微观组织、宏观织构和室温力学性能.结果表明,随着轧制道次的增加,板材的晶粒组织出现交替细化与粗化的现象,并直接影响板材后续退火组织的大小和均匀性.由于累积剪切变形的作用,等径角轧制后板材的基面织构明显弱化.七道次等径角轧制后基面极轴出现沿轧向分离,板材屈服强度降低约54%,而伸长率提高约43%.基面织构弱化和晶粒细化是等径角轧制板材塑性提高的主要原因.     

不同初始态Mg-Zn-Gd加工过程中组织和性能的演变

主要研究了初始状态分别为轧态和退火态的Mg-2%Zn-1%Gd合金在360℃进行单道次66%大压下轧制和其后的退火加工过程中组织和性能的演变规律.通过金相观察、拉伸实验和杯突实验分析表明:不同初始状态Mg-Zn-Gd合金随着加工过程的进行其力学性能及演化规律也明显不同.这是由对应组织中的剪切带、孪生密度和晶粒尺寸共同决定的.初始退火态Mg-Zn-Gd合金经大压下轧制和热处理加工之后表现出了更优秀的机械性能和更小的各向异性,其最终伸长率可达289%.初始为退火态的Mg-Zn-Gd合金板材最终制得的薄板在室温下的成形性更好.     

热轧工艺对409L铁素体不锈钢深冲性的影响

对含有单一柱状晶的409L铁素体不锈钢连铸坯,采用不同终轧温度的热轧工艺,由常规热轧转变为温轧,再经过相同后续工艺;较低终轧温度的成品获得了较高rm值和较低△r值.终轧温度的降低使组织演变发生变化:热轧和冷轧组织中晶界和晶内剪切带增多,变形组织被细化、硬化,尤其是中心层附近的粗大带状晶粒;两者的增多又增加了退火过程中的...     

微观组织和织构对H65黄铜带材折弯性能的影响

电子产品关键部件小型化对黄铜合金带材折弯性能提出了更高的要求。研究了微观组织和织构对H65黄铜带材折弯性能的影响规律和影响机制。结果表明：带材平行于轧向折弯较垂直于轧向折弯更易于产生表面褶皱和裂纹,且随着折弯半径的减小,折弯性能降低。折弯变形过程中带材外表面易形成剪切带,所产生的剪切变形是造成表面褶皱和开裂的主要原因。微观组织不均匀、较强的Brass织构易导致带材折弯过程中产生剪切变形,造成带材折弯性能下降。通过调控热处理工艺来调整带材织构,减少或抑制剪切带的产生,能够提升带材的折弯性能。     

Effect of cold rolling process on microstructure and mechanical properties of high strength β titanium alloy thin sheets

The microstructure and mechanical properties of Ti-3.5Al-5Mo-6V-3Cr-2Sn-0.5Fe high strength titanium alloy sheets prepared by unidirectional cold rolling and two-step cross cold rolling were investigated. Results showed that the β phase grains were refined significantly by cold rolling followed by solution treatment for a short time.Compared to unidirectional cold rolling, the short time solution treatment after two-step cross rolling could significantly reduce the non-uniformity of the microstructure of the alloy sheets. After aging treatment at 550 ℃,the anisotropy of the mechanical properties still existed in the unidirectional rolled sheets, and the tensile strength was highest along the rolling direction. After solution and aging treatment, the anisotropy of the mechanical properties of the two-step cross rolling process sheet was not obvious than unidirectional cold rolling,and alloy had good strength and plasticity matching.     

预处理对高应变速率轧制镁合金板材组织均匀性和力学性能的影响

传统的镁合金板材加工技术存在生产效率低、成本偏高和成形性能不够理想等局限.本论文采用高应变速率轧制对AZ31镁合金进行轧制,对比研究了两种预处理方法对板材组织性能的影响.结果表明,高应变速率轧制是获得具有细小晶粒组织和良好综合力学性能的镁合金板材的有效手段.经过预变形+均匀化的预处理,高应变速率轧制板材的组织均匀性得到...     

异径轧制对AZ31镁合金薄带微观组织的影响

考虑到轧制镁合金薄带板形的控制精度要求,采用小辊径同径轧制和异径轧制工艺分别制备了0.5,1.0 mm的AZ31镁合金薄带,研究不同工艺过程中板材内部晶粒微观组织的变化规律以及同径轧制与异径轧制在轧制过程中的对称性问题.结果表明:0.5 mm异径轧制和同径轧制板带的晶粒尺寸分别为8.8和10.1μm,1.0 mm的分别为13.6和16.7μm.0.5 mm的异径轧制与同径轧制的单元等效塑性应变最大值分别为0.42和0.29,1.0 mm的分别为0.75和0.66,与实验结果相符.0.5 mm同径轧制的特征节点在板带上中下部的等效米塞斯应力和剪切应力分布对称,异径轧制的分布非对称.0.5 mm板带经过250,300,350℃退火1 h后,异径轧制的晶粒长大较缓慢,同径轧制的晶粒长大较快.350℃下,异径轧制的晶粒尺寸为9.8μm,同径轧制的为24.9μm.     

轧制Fe_(81)Ga_(19)合金薄带再结晶织构演变

对Fe_(81)Ga_(19)合金进行冷轧与再结晶退火,考察了压下率对再结晶织构及磁致伸缩性能的影响.再结晶织构主要由Goss({110}001)和γ(111//ND)织构组成,再结晶织构特征随压下率增加出现明显的改变,归因于变形微结构与冷轧织构的差异.冷轧压下率从60%增加到70%时,剪切带密度增加且{111}112形变织构增强,提高再结晶Goss织构强度与磁致伸缩性能.压下率为80%时,剪切带与形变基体取向变化使剪切带晶核取向漫散,且晶界储能提高为再结晶γ织构提供更多形核位置,导致再结晶Goss织构减弱而γ织构增强,降低薄带磁致伸缩性能.     

Characteristics of AZ31 Mg alloy joint using automatic TIG welding

The automatic tungsten-inert gas welding (ATIGW) of AZ31 Mg alloys was performed using a six-axis robot. The evolution of the microstructure and texture of the AZ31 auto-welded joints was studied by optical microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and electron backscatter diffraction. The ATIGW process resulted in coarse recrystallized grains in the heat affected zone (HAZ) and epitaxial growth of columnar grains in the fusion zone (FZ). Substantial changes of texture between the base material (BM) and the FZ were detected. The {0002} basal plane in the BM was largely parallel to the sheet rolling plane, whereas the c-axis of the crystal lattice in the FZ inclined approximately 25° with respect to the welding direction. The maximum pole density increased from 9.45 in the BM to 12.9 in the FZ. The microhardness distribution, tensile properties, and fracture features of the AZ31 auto-welded joints were also investigated.     

6111铝合金在冷轧过程中织构的变化

采用取向分布函数(ODF)分析并研究了6111铝合金在冷轧过程中织构的演变及轧制工艺对冷轧织构的影响.结果表明,6111铝合金冷轧后,主要轧制织构组分均为Copper织构组分、S织构组分和Brass织构组分;冷轧过程中,在一定条件下会产生较强的旋转立方织构,而且继续轧制时,随着轧板的减薄,旋转立方织构会迅速减弱而Copper,Brass,S等正常轧制织构组分迅速增强.此外,在总轧制形变量相同的条件下,随着道次压下率的提高,轧制织构减弱.     

难变形材料轧制实验机开发及实验研究

为满足难变形材料轧制实验研究,开发新型实验轧机.采用液压张力缸和液压夹头夹持短试样,实现直拉张力轧制.采用两台主电机对上下工作辊单独传动和速度调整,实现异步轧制时速度比连续调整.将夹持轧件两端的夹头作为正负极,通低电压大电流,对轧件进行电阻加热,实现温轧功能.利用该新型实验轧机进行验证实验.对3%Si无取向硅钢进行带张力异步轧制,异步比设定为1.12,总压下量增大28.4%.对AZ31镁合金进行带张力温轧实验,厚度由4 mm轧制到0.633 mm,顺利完成轧制并得到很好的表面质量.实验表明,该实验轧机可以作为难变形材料轧制实验研究的有力工具.     

热轧工艺中加热温度对IF钢组织性能的影响

选取Ti-Nb-IF钢热轧工艺中的加热温度为影响因素,采用显微观察、TEM二相粒子分析、织构分析等实验分析手段,研究了1 140℃和1 214℃两种热轧加热温度制备的Ti-Nb-IF钢样品在随后的冷轧、退火和平整过程中显微组织演变和织构演变特征的影响及最终产品的力学性能.结果表明,低温加热有利于IF钢屈强比的降低及深冲性能的提高,加热温度为1 140℃比1 214℃,其屈服强度可降低30 MPa,塑性应变比可提高0.16.其主要原因为低温加热工艺保障IF钢热轧后产生粗大的二相粒子和细小铁素体晶粒,在随后的冷轧和退火处理过程中产生分布均匀和强的γ再结晶织构.     

Effects of asymmetric rolling process on ridging resistance of ultra-purified 17%Cr ferritic stainless steel

In ferritic stainless steels, a significant non-uniform recrystallization orientation and a substantial texture gradient usually occur, which can degrade the ridging resistance of the final sheets. To improve the homogeneity of the recrystallization orientation and reduce the texture gradient in ultra-purified 17%Cr ferritic stainless steel, in this work, we performed conventional and asymmetric rolling processes and conducted macro and micro-texture analyses to investigate texture evolution under different cold-rolling conditions. In the conventional rolling specimens, we observed that the deformation was not uniform in the thickness direction, whereas there was homogeneous shear deformation in the asymmetric rolling specimens as well as the formation of uniform recrystallized grains and random orientation grains in the final annealing sheets. As such, the ridging resistance of the final sheets was significantly improved by employing the asymmetric rolling process. This result indicates with certainty that the texture gradient and orientation inhomogeneity can be attributed to non-uniform deformation, whereas the uniform orientation gradient in the thickness direction is explained by the increased number of shear bands obtained in the asymmetric rolling process.     

Effects of the types of overlap on the mechanical properties of FSSW welded AZ series magnesium alloy joints

The effects of the types of overlap on the mechanical properties of the friction stir spot welding (FSSW) welded AZ series magnesium alloy joints were investigated by microstructural observations, microhardness tests, and tensile tests. The results show that the microstructure of the stir zone adjacent to the periphery of the rotating pin is mainly composed of the upper sheet. The average distance D between the longitudinal segment of the curved interface and the keyhole periphery, the tensile shear force, and the microhardness of the stir zone of the FSSW welded AZ61 alloy joint are the highest in all samples. During FSSW of AZ31 and AZ61 dissimilar magnesium alloys, the irregular deformation of the longitudinal segment of the curved interface appears, while the microhardness of the stir zone is higher when AZ61 alloy is the upper sheet. Moreover, the microhardness of the stir zone increases initially and then decreases sharply in the longitudinal test position.     

Ti-IF和Ti+Nb-IF钢铁素体区热轧组织和织构特征

选择Ti-IF和Ti+Nb-IF钢铁素体区热轧板为实验材料,采用金相组织观察、二相粒子形貌分析、织构分析等实验手段对其组织和织构特征进行了分析.结果表明:Ti-IF钢比Ti+Nb-IF钢的晶粒尺寸大,二相粒子尺寸大且数量多;两种钢的表层板织构强弱正好相反且在二分之一层形成了具有冷轧特征的织构,而纤维织构表层为(1 1 0)∥ND,(1 1 2)∥ND,(1 0 2)∥ND,二分之一层为(0 0 1)∥ND,(1 1 1)∥ND,(1 1 2)∥ND;区别于Ti+Nb-IF钢,Ti-IF钢在表层出现了〈0 0 1〉∥RD,二分之一层出现了〈1 0 2〉∥RD织构组分.     

微碳钢铁素体区热轧试验研究

在连铸连轧生产线采用铁素体轧制技术制备微碳钢热轧薄板,并对所制备薄板的组织、性能及织构进行分析。结果表明:铁素体轧制微碳钢热轧薄板的组织为完全再结晶铁素体,平均晶粒尺寸50 m左右。相对于常规奥氏体轧制,铁素体轧制薄板的屈服强度和抗拉强度分别下降了21%和6%,延伸率略有下降。热轧薄板的塑性应变比值为0.4,明显低于常规奥氏体轧制。薄板中存在较强的{001}织构是导致值较低的主要原因。     

应力状态对AZ31镁合金最佳成形温度的影响

在20～250℃温度范围内,对AZ31镁合金薄板进行了单向拉伸、筒形件拉深以及胀形试验,并用金相显微镜观察了试验后试件的显微组织。分析了AZ31镁合金在不同工艺所对应的应力状态下塑性变形特点及其最佳成形温度。结果表明,变形过程中所受应力状态对AZ31镁合金最佳成形温度的影响很大,AZ31镁合金在成形过程中受单向拉应力时,其总延伸率随成形温度的升高而增加;应力状态主要为压应力时,最佳成形温度应在tr=1以下;而应力状态主要为双向拉应力时,其最佳成形温度应在tr=1以上。