低浓度Cu-Al2O3弥散强化铜合金拉伸断裂特性的研究

通过力学性能测量、金相以及SEM观察对不同状态低浓度Cu-0.23vol%Al2O3弥散强化铜合金的断裂行为进行了研究.结果表明:合金经过单向冷轧变形后,无论是冷轧态还是退火态纵向强度、伸长率均高于横向.纵向工程应力-应变曲线仅发生一次断裂,但是横向工程应力-应变曲线却出现"二次断裂"现象.出现"二次断裂"现象的原因可能是,经冷轧变形后的弥散强化铜合金组织呈纤维状,而纤维界面为弱结合面,裂纹易于在界面上形成和扩展,在横向拉应力作用下极易导致几层纤维组织优先被"劈开",出现"一次断裂";在继续拉伸过程中其他部位不断"劈开",合金的工程应力-应变曲线出现"二次断裂"现象,并给出了纵横向拉伸断裂模型图.     

横轧3 104铝合金变形织构的研究

应用极图分析及织构定量计算的方法，研究了横轧对3104铝合金变形织构的影响，结果表明：在与常规轧制相同压下量的横向轧制下，3104铝合金中的｛112｝，｛213｝丝织构体积百分数均低于常规轧制时各组分的体积百分数，而横向轧制则使得｛102｝丝织构增加较多，在横向轧制过程中出现强旋转立方织构和新｛110｝＜557＞取向的织构。     

冷轧对新型Ni-W-Co-Ta高密度合金组织与性能的

在室温环境中对新型Ni-W-Co-Ta高密度合金进行冷轧变形，借助金相显微镜、扫描电镜、透射电镜、X射线衍射仪、背散射电子衍射、电子万能试验机及显微硬度计对新型Ni-W-Co-Ta高密度合金变形过程中的微观组织及力学性能演变规律进行表征。结果表明：随着变形量的增加，新型Ni-W-Co-Ta高密度合金等轴晶粒沿轧制方向不断被拉长，同时产生大量的滑移带协调剧烈的塑性变形，并最终形成纤维组织。变形量的增大导致位错密度急剧增加，位错交互作用显著加强，进而将晶粒尺寸细化至25.5 nm。经过90%的严重塑性变形后，抗拉强度提高到1953 MPa；屈服强度提升至1806 MPa，硬度增加至534 HV，伸长率则急剧下降至9.1%。断口形貌则由韧性断裂向韧性-准解理混合型断裂转变。     

不同拉伸温度下SiC颗粒增强Al-Fe-V-Si复合材料的断裂行为

采用喷射沉积工艺制备SiCP/Al-11.7Fe-1.15V-2.4Si复合材料,并通过热压工艺对复合材料进行致密化,再通过热轧加工成板材。对复合材料的显微组织以及不同温度下复合材料的断裂性能和断口形貌进行研究。结果表明:采用热压致密后再热轧工艺能使SiC颗粒分布均匀,长轴方向平行于轧制方向,有利于增强复合材料的力学性能,复合材料的断裂性能和断面形貌与拉伸温度以及SiC的分布和取向相关,随着拉伸温度升高,SiC/Al界面强度减弱,拔断的SiC颗粒逐渐减少,SiC颗粒的拔出成为主要的裂纹源;与基体金属不同的是,复合材料的塑性随着温度升高而降低。     

Effect of thermomechanical processing on microstructure and mechanical properties of CoCrFeNiMn high entropy alloy

The CoCrFeNiMn high entropy alloy was produced by homogenization, cold rolling and recrystallization. The effects of thermomechanical processing on microstructures and tensile properties at different temperatures were investigated using X-ray diffractometry (XRD), optical microscopy (OM), scanning electron microscopy (SEM) and multi-functional testing machine. The results show that dendritic structures in cast alloy evolve into equiaxed grains after being recrystallized, with single face-centered cubic (FCC) phase detected. The most refined alloys, stemming from the highest rolling ratio (40%), exhibit the highest strength due to the grain boundary strengthening, while the variation of elongation with temperature shows a concave feature. For the coarse-grained alloys, both the ductility and work hardening ability decrease monotonically with increasing temperature. Serrated flow observed at intermediate temperatures is attributed to the effective pinning of dislocations, which manifests the occurrence of dynamic strain hardening and results in the deterioration in ductility. Besides, dimples on the fracture surfaces indicate the typical ductile rupture mode.     

AZ31B镁合金轧制板材室温动态拉伸的SEM观察

利用动态拉伸台和扫描电镜(SEM)对AZ31B镁合金轧制板材进行了动态拉伸的微观形貌观察。试验证明,材料宏观织构和显微组织都会对镁合金轧制板材的室温拉伸性能产生影响;在轧制镁合金拉伸变形时滑移和孪生同时存在;裂纹的产生和扩展具有明显的方向性。轧制组织中大量的变形孪晶与应力方向的位向关系,是轧向和横向上裂纹产生及扩展机制产生较大差异的主要原因。     

预变形及时效处理对7055铝合金组织和性能的影响

通过拉伸试验、金相观察、X射线衍射以及TEM观察，研究了7055铝合金固溶处理后，经不同程度冷变形和时效后的力学性能和电导率的变化以及相应的微观组织变化特点。实验结果表明，对于冷变形再T6时效的7055铝合金，随变形量的提高，强度先略有上升，而后缓慢下降。RRA态合金强度随变形量增加而持续下降。随变形量的增加，冷轧态7055铝合金的电导率逐渐下降，而T6和RRA态合金的电导率却逐渐上升。在同样变形量条件下，RRA态合金具有最高的电导率。这些变化与变形引入的位错所产生的晶格畸变以及位错促进粗大平衡相析出有关。     

Al-6Mg-0.8Zn-0.5Mn-0.2Zr-0.2Er合金高强耐损伤工艺与微观组织研究

以Al-6Mg-0.8Zn-0.5Mn-0.2Zr-0.2Er合金为基础,对该材料的冷轧态,温轧态,完全退火态进行拉伸测试和疲劳裂纹扩展速率测试。运用电子背散射衍射(EBSD),透射电镜(TEM),扫描电镜(SEM)对合金的原始组织、疲劳断口、裂纹扩展路径进行观察,研究微观组织对材料拉伸性能及疲劳裂纹扩展速率的影响。结果表明:温轧态屈服强度高,裂纹扩展抗力大,实现了高强高耐损伤性能的匹配。这主要是由于温轧态轧制过程中发生动态回复,位错缠结规整化,具有较多的亚晶界,该种组织模式对材料的屈服强度和疲劳裂纹扩展抗力均有提高。     

冷轧带钢倾斜浪缺陷产生机理分析及控制研究

冷轧带钢倾斜浪缺陷即带钢表面斜纹是冷连轧产品普遍存在的一种板形缺陷,其产生机理及调控手段尚不清楚。介绍了倾斜浪缺陷的特征;进行了轧制规程调整、轧机设备精度调整等轧制试验。结果表明,双边浪轧制和调节五机架前后张力对倾斜浪缺陷有较为明显的影响。综合理论分析和试验结果,认为轧机出口带钢横断面张力不均,造成张力大的部分条元延伸率大,即造成带钢横断面的金属纵向延伸率不同,不能均匀纵向流动,且产生横向流动,各条元之间产生相互作用的内应力,当内应力足够大就会引起带钢翘曲;此条元的带钢翘曲后,张力变小,相邻条元的张力变大,带钢翘曲沿着带钢纵向斜的方向移动,便产生了倾斜浪缺陷。为此,提出了采用双边浪轧制和调整五机架前后轧制张力共同抑制倾斜浪缺陷的方法,试验结果表明倾斜浪缺陷改善明显。     

Effects of Pack Rolling Temperature on Microstructure and Mechanical Properties of Powder Metallurgical Ti-45Al-7Nb-0.3W Alloy

Powder metallurgical Ti-45Al-7Nb-0.3W (at.%) alloys were pack rolled at temperatures of 1240°C, 1255°C, 1270°C, and 1285°C. The microstructures were investigated by scanning electron microscopy (SEM) and transmission electron microscopy. The tensile properties were tested at room temperature and 800°C. After rolling, the sheets exhibited duplex microstructures with refined grains. The tensile test results showed the sheet rolled at 1270°C displayed excellent room temperature tensile properties with an ultimate tensile strength (UTS) of 782 MPa and an elongation of 1.95%. When tested at 800°C, all sheets showed UTS of over 600 MPa and elongations of around 50%. The dislocation movements and mechanical twinning played important roles at the initial stage of rolling deformation. However, during the subsequent deformation process, the deformation mechanism should mainly be the result of dynamic recrystallization.     

Ti70合金板的组织与力学性能的各向异性

通过拉伸及低温冲击试验、光学显微镜、扫描电镜及X射线衍射仪,对Ti70合金板的组织与力学性能的各向异性进行了研究。结果表明,Ti70合金板热轧及退火后组织未出现明显差异,退火过程中主要以回复为主,但在高密度位错的剪切带上出现了一定数量的再结晶晶粒。退火态Ti70合金板横向屈服强度及低温冲击吸收能量都高于纵向,但抗拉强度低于纵向,表现出了明显的各向异性。退火后Ti70合金板形成了较强的{0002}基面织构,其晶面法向向RD方向(纵向)偏转±30°,向TD(横向)方向偏转±41°。由于基面织构更向RD方向集中,因此造成了Ti70合金板力学性能的各向异性。     

Effect of grain shape on the texture evolution during cold rolling of Al-Mg alloys

The hot bands of continuous cast AA 5754 and high-Fe AA 5754 aluminum alloys exhibited elongated grains in the rolling direction after recrystallization annealing. The annealed hot bands were cold rolled to different reductions along the original rolling direction and transverse direction, respectively. The effect of grain shape on texture evolution was investigated by X-ray diffraction. It was found that straight-rolling resulted in a higher rate of disappearance of the r-cube + cube component and a slightly higher rate of formation of the β fiber component than cross-rolling. The elongated grains in the rolling direction were easier to rotate from initial orientations to the β fiber in straight-rolling than in cross-rolling.     

Effect of rolling process on microstructures and mechanical properties of AZ31B alloy sheets

AZ31B magnesium extruded slabs prepared from LFEC were rolled at fairly lower temperature at 3, 6 and 16 m/min rolling speeds into 1 mm thickness. The results indicate that the microstructures achieved by rolling at low temperature or at low rolling speed are composed of many prismatic regions divided by shear strips due to pile-up of twin crystals; the prismatic regions increase at elevated rolling temperature or at high rolling speed, and finally all are composed of equiaxed crystals without twin crystals due to dynamic recrystallization. After optimizing control of rolling process, excellent mechanical properties would be acquired. The mechanical properties ofAZ31B sheet are ab=350 MPa, cr0.2=300 MPa, and 3=12.0% when rolled at 6 m/min. At the same time, the difference of mechanical properties between transverse and longitudinal direction reduced markedly.     

Texture development and hardening characteristics of steel sheets under plane-strain compression

Crystallographic texture development and hardening characteristics of a hot-rolled, low-carbon steel sheet due to cold rolling were investigated by idealizing the cold rolling process as plane-strain compression. The starting anisotropy of the test material was characterized by examination of the grain structure by optical microscopy and the preferred crystal orientation distribution by x-ray diffraction. Various heat treatments were used in an effort to remove the initial deformation texture resulting from hot rolling. The plastic anisotropy of the starting material was investigated with tensile tests on samples with the tensile axis parallel, 45°, and perpendicular to the rolling direction. The grain structure after plane-strain compression was studied by optical microscopy, and the new deformation texture was characterized by x-ray diffraction pole figures. These figures are compared with the theoretical pole figures produced from a Taylor-like polycrystal model based on a pencil-glide slip system. The uniaxial tensile stress-strain curve and the plane-strain, compressive stress-strain curve of the sheet were used to calibrate the material parameters in the model. The experimental pole figures were consistent with the findings in the theoretical study. The experimental and theoretical results suggest that the initial texture due to hot rolling was insignificant as compared with the texture induced by large strains under plane-strain compression.     

轧制方向对Fe-3％Si合金织构演变规律的影响

形成锋锐的Goss织构是取向硅钢获得优异磁性能的关键, 初始样品表层中较强的Goss织构对最终的强Goss织构起重要作用. 本文通过改变硅钢冷轧方向获得不同的初始织构及初始组织, 考察热轧板表层及中心层不同的组织及织构的进一步变化对一次冷轧、中间退火、二次冷轧及脱碳退火、二次再结晶退火后的织构及组织变化规律的影响. 探讨了这些特殊方式制备的样品中Goss织构的形成条件. 结果表明, 强烈的初始组织及织构的差异随轧制及退火次数的增多逐渐消失; 最终二次再结晶都可顺利进行, Goss织构及磁性能差异并不大. 虽然初始样品中Goss织构的强弱差异很大, 但因各阶段都可以形成较强的 {111}<112>织构, 弥补了初始样品中Goss织构过弱的不足, 因此轧制方向及初始组织都对最终的织构影响不大. 研究还证实了立方织构的遗传性; 横向轧制是消除稳定的{112}<110>轧制织构的有效方法.     

冷轧对M50钢马氏体/贝氏体复相组织与力学性能的影响

利用X射线衍射仪(XRD) 、扫描电镜(SEM) 、透射电镜(TEM)、室温拉伸和冲击性能测试研究了冷轧对M50钢马氏体/贝氏体(M/B)复相组织和性能的影响。结果表明:20%冷轧变形量的试样经等温淬火后具有最佳的抗拉强度(2535.7 MPa)和冲击性能(96.93 J),相比变形量为0%的试样,冲击吸收能量提高了约21%,抗拉强度提高了约5%。当变形量小于20%时,随着变形量的增加,M/B复相组织逐渐细化且在20%的冷轧变形量下组织最细;当变形量大于20%时,随着变形量的增加,贝氏体束减少,其对马氏体板条的分割作用减弱,导致组织呈现一定的粗化。     

超细晶钢微观组织与力学性能的各向异性研究

通过温轧技术,成功制备了平均晶粒尺寸约1 μm的超细晶钢。利用扫描电镜、电子背散射衍射和室温拉伸等检测手段,研究了超细晶钢板的微观组织与力学性能的各向异性。结果表明:制备的超细晶钢板不同方向的微观组织和力学性能具有明显的各向异性;纵截面表层和心部的晶粒大多呈现拉长的形态,同时表层的晶粒拟合椭圆长/短轴比相较于心部更小,形状更加接近于圆形,横截面的晶粒拉长状特征相较于纵截面减弱,更接近等轴态,晶粒在三维空间呈细长的扁梭形态;各向强度由高到低依次为轧向、横向、与轧向成45°方向;长梭形晶粒组成的微观组织形态和织构是导致超细晶钢板力学性能各向异性明显的主要原因。     

热加工对冷喷涂铝合金块材性能的影响

为了提高冷喷涂增材制造铝基块材性能，对低压冷喷涂法沉积的7075铝合金块材进行了后续退火和热轧加工。采用光学显微镜和扫描电镜观察试样的组织结构特征，并通过拉伸试验和电化学测试表征了块材的应力-应变曲线和耐蚀性。结果表明，低压冷喷涂法沉积的铝合金块材结构上存在大量的颗粒界面和少量微孔等缺陷，拉伸时发生脆性断裂，塑性很差，耐点蚀性能差；经过400℃退火4 h后，结构缺陷显著减少；再经过30%压下量的热轧加工后，结构更加致密，强度和韧性均提高，耐蚀性也随着结构缺陷的减少而提高。     

Influence of rolling route on microstructure and mechanical properties of AZ31 magnesium alloy during asymmetric reduction rolling

Four different routes of asymmetric reduction rolling were conducted on AZ31 magnesium alloy to investigate their effect on the microstructure evolution and mechanical properties. Route A is the forward rolling; while during routes B and C the sheets are rotated 180° in rolling direction and normal direction, respectively; route D is the unidirectional rolling. The strain states of rolled sheets were analyzed by the finite element method, while the microstructure and texture were observed using optical microscopy, X-ray diffraction and electron back-scattered diffraction techniques, and the mechanical properties were measured by tensile test. The results show that route D produced the largest effective strain. Compared with other samples, sample D exhibited a homogeneous microstructure with fine grains as well as a weak and tilted texture, in corresponding, it performed excellent tensile properties, which suggested that route D was an effective way to enhance the strength and plasticity of AZ31 sheet.     

低镍奥氏体不锈钢冷轧边裂原因分析

针对低镍Cr-Mn-Ni-N奥氏体不锈钢冷连轧过程中的边裂问题,采用金相显微镜、扫描电子显微镜分析了断口、边裂位置附近、正常位置显微形貌;分析了冷轧带钢横向应力、轧制力分布规律。结果表明,钢中镍元素偏析、存在Al₂O₃夹杂物、形变马氏体组织含量增加,以及带钢边部应力、轧制力较大,是导致低镍奥氏体不锈钢冷连轧过程出现边裂,甚至导致断带的主要原因。为此,提出了连铸冷却模式采用弱冷;在热连轧铸坯加热及后工序带钢固溶退火工艺中对材料合金元素进行均质化处理;优化冷连轧工艺,保证第1道次压下率为30%~35%,总压下率为50%~68%,使马氏体形变组织得到有效控制;保证原料楔形、板凸度等在合理范围内,并通过调整弯辊力来改善轧制力的横向分布等措施,使带钢轧后边裂断带率由0.98%降至0.25%。