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.     

驱动辊转速对环件轧制工艺影响规律研究

针对环件轧制成形规律,以数值仿真和数学解析相结合的方法,以有限元分析软件ABAQUS为平台,建立弹塑性动态显式有限元模型,研究驱动辊转速对环件成形工艺的影响。研究表明,在环件轧制过程中,随着驱动辊转速的增加,每转进给量减小,外径部分金属轴向流动增加,环件自由端面形状系数FT增加,最大宽展系数增加,环件自由端面质量下降;在驱动辊转速增加过程中,轧制力和轧制力矩减小,对轧环机的力学性能要求降低。同时平均等效应变PEEQa增加,环件塑性变形程度增大,有利于提高环件力学性能,但同时变形不均匀程度也加大,内部质量缺陷的可能性增加。     

Microstructure and mechanical properties of AM31 magnesium alloys processed by differential speed rolling

Ingot casted AM31 alloys were rolled at a warm temperature of 350 °C and subsequently rolled at 300 °C using equal speed rolling (ESR) and differential speed rolling (DSR) with speed ratios of top roll to bottom roll, 1.2 and 1.5, respectively. Microstructures, textures and mechanical properties of the as-rolled AM31 sheets were examined. Ductility was improved by DSR due to inclination of basal poles and weakened texture. The sheets produced by DSR with a speed ratio of 1.2 showed highest strength and ductility at room temperature, which can be attributed to homogeneous fine grain distribution and tilted basal texture.     

椭圆孔型宽高比对线材表面变形状态的影响

针对高速线材在不同宽高比的椭圆孔型中轧制时的表面变形问题,采用非线性有限元方法,从等效塑性应变及塑性应变能密度的角度说明椭圆孔型宽高比对线材表面变形状态的影响.研究表明,线材在不同宽高比的椭圆孔型中具有相同的变形规律,轧件与轧辊接触临界点附近线材表面变形差异最大,塑性应变及应变能密度在此处出现峰值,易形成褶皱缺陷.减小...     

无缝钢管斜轧工艺理论中的有关问题

在论述无缝钢管斜轧工艺理论中有关辊形与变形区的关系、速度分析以及金属塑性变形特征理论概念的基础上,提出了辊形与变形区解析、速度分析计算以及轧管变形工具的合理设计等方法。     

Texture of AZ31B magnesium alloy sheets produced by differential speed rolling technologies

The effects of differential speed rolling (DSR) on the texture of AZ31B magnesium alloy sheets were investigated,which were achieved by tailoring deformation temperature,reduction,and speed ratio.The results show that the intensity of basal texture weakens with DSR.With the increase of the rolling temperature,the intensity of basal texture decreased first and then increased,which had a relation with the change of the orientation of the new grains of dynamic recrystallization during rolling.The effect of the reduction on the basal texture was made with the changing degree of sharp point of texture.With increasing the deformation at the same rolling temperature,the intensity of basal texture decreased,and the extending of contour lines decreased in the transverse direction,which was close to the circular distribution.Differential speed ratio has a greater impact on the intensity of the basal texture and has a less effect on the basal deflection.     

Microstructure and mechanical properties of AZ31 magnesium alloy sheets produced by differential speed rolling

The as-extruded AZ31 alloy sheets of 10 mm in thickness were subjected to differential speed rolling (DSR) process performed on a mill, of which the rotation speed ratio of the lower roll and upper one is kept at constant 1.05 by using the different upper and lower roller diameters. The influence of the billet temperature, pass and total thickness reduction ratio on the microstructures, mechanical properties and crystal orientation of the specimens were examined by optical microscopy, tensile test and X-ray diffraction. The present process was found to be effective to refine the grain size and restrain the twinning. Grain refinement became more marked and uniform when the pass and total thickness reduction ratio increased, and the sheets processed by DSR exhibited higher elongation and lower strength than those of the conventional rolled sheets under the same testing conditions. Especially, the AZ31 sheet with elongation of 32% at room temperature was prepared. Moreover, anisotropy was diminished by further annealing at 573 K for 30 min. The DSR does not alter the basal texture but leads to the incline of the basal plane from the sheet surface plane to some extent.     

Effect of differential speed rolling on microstructure and mechanical properties of an AZ91 magnesium alloy

Severe deformation by differential speed rolling (DSR) with a high-speed ratio could be successfully imposed on the AZ91 plate to produce thin sheets with submicron grain size and good planar isotropy. The sheets exhibited a good combination of high strength and high ductility, showing yield stresses of 327 MPa and tensile elongations of 9–11%. Comparison with other severe deformation processes indicates that DSR process is advantageous over ECAP process in obtaining higher strength and over ARB process in obtaining higher ductility. Moreover, the current DSR is a continuous process as well as a convenient method of imposing severe deformation on thin Mg sheets.     

The effect of retained austenite stability on high speed deformation behavior of TRIP steels

The safety of passengers is important during an automobile collision. Because a collision event involves high speed deformation, it is necessary to develop property data and understand the applicable deformation mechanisms to aid in the selection of proper materials for crash-related automotive components. Therefore, dynamic mechanical properties of low carbon TRIP steels with varying retained austenite stabilities were evaluated over a wide range of strain rates using a high-velocity hydraulic tensile testing machine. Tensile tests were performed at strain rates ranging from 10² to 6×10² s¹ using standard ASTM E-8 specimens with an elastic strain gage attached to the sample grip end to measure load, and a plastic strain gage mounted onto the gage section to measure strain. Ultimate tensile strengths (UTS), strain rate sensitivities, and strain hardening behaviors are reported. TRIP steel with high stability retained austenite exhibited higher yield stress, lower UTS and lower strain hardening than TRIP steel with low stability retained austenite.     

铝钢复合带材异径轧制变形规律的研究

以4A60铝合金和08Al低碳钢为研究对象,利用异径轧机进行异径同速轧制,从厚度变化、硬度分布及金相组织等几个方面对薄铝复层的铝/钢轧制复合变形区的金属流动规律进行了研究分析。结果表明：铝钢轧制复合过程中铝先于钢达到稳定塑性变形,轧制复合过程中变形区可分为铝钢变形未复合区、铝钢变形复合区和钢变形区。当变形量增加到55%时,钢的硬度从约110 HV升高到210 HV,而铝层的硬度变化不大,基本保持在（40±5） HV。4A60铝和08Al钢的临界复合压下量为15%左右,当压下量超过45%时,仅发生钢的变形,而铝的厚度基本保持不变。铝层厚度与总厚度的比值（复合比）由轧前的0.054降低到轧后的0.052,说明轧制复合过程中铝的变形更大。     

W6高速钢/16Mn钢电子束焊接接头组织及性能分析

高速钢作为一种高硬度、高耐磨性和高耐热性特殊工具钢,应用于刀具、模具及特殊结构件上时,往往需要结合异种钢使用. 但高速钢焊接工艺研究仍不成熟,焊接中产生的裂纹与碳化物缺陷是制约高速钢应用的主要因素. 文中通过对W6Mo5Cr4V2高速钢与16Mn钢预置镍填充层后进行电子束焊接. 结果表明,镍中间层的引入有效的抑制了高速钢侧热影响区的开裂,接头呈不对称“漏斗形”. 焊缝组织主要由镍基固溶体与少量M₂C碳化物构成,焊缝中无马氏体组织,其焊缝平均硬度为185 HV;接头抗拉强度达到378 MPa,为16Mn侧母材抗拉强度的75%. 拉伸断口断裂于距W6侧熔合线0.8 mm处的热影响区,为准解理断裂.     

辊式校平过程对船用大尺寸10Ni5CrMoV钢板材初始残余应力的影响

用实验和数值模拟相结合的方法,研究了辊式校平过程对10Ni5CrMoV钢大尺寸船用板材残余应力的影响规律。实验结果和有限元结果的对比表明,大尺寸板材的辊式校平的有限元分析过程可以用平面应变问题来处理,并能保持相当的精度;校平过程对于板材上表面的长度方向应力影响很大。有限元分析的结果表明,校平过程中板材承受反复的拉压,从而在板材表面形成一层关于中性层对称的塑性变形。     

The impact of corrosion on the mechanical behavior of steel undergoing plastic deformation

In the present study the influence of the degree of plastic strain, due to various levels of plastic deformation during bending, on the mechanical properties of class BSt 500_s tempcore steel was investigated, under various levels of salt spray corrosion. The resulted mass loss was of realistic levels and comparable to the one created by natural environmental causes. The results showed that even though an increase in plastic deformation resulted in an expected marginal increase in strength properties, it had a negative effect in ductility. The international community has not reached a consensus yet concerning the minimum required bending roll diameter, for stirrup production, which ranges between 4–10 times the diameter of the steel bar to be bent. It was also shown that this combination is crucial since strain fractures were recorded under the minimum required values set by the most current design guide‐lines and design oriented research. The results of this investigation are intended to offer an in depth understanding of the impact of the underestimated factor of corrosion on the mechanical properties of steel undergoing plastic deformation in corrosive environments and to show the need of re‐examination of existing codes.     

Effect of SiC Nanoparticles on Bond Strength of Cold Roll Bonded IF Steel

In this study, cold roll bonding process characteristics of IF steel strips, such as bond strength, threshold deformation, undulation of peeling force, and peeled surface, in the presence of SiC nanoparticles were examined and compared to those of an IF steel strip without nanoparticles. The bond strength was evaluated by the peeling test and scanning electron microscopy. It was found that when the thickness reduction was increased, the peeling force of IF steel strips improved. The results also indicated that the presence of silicon carbide nanoparticles decreased the bond strength of IF steel strips when compared to the strips without nanoparticles for the same thickness reduction. When the thickness reduction was increased, the undulation of average peeling force values increased at a constant nanoparticle content. Also, the strips without nanoparticles had a lower undulation value as compared to the strips with SiC nanoparticles. In addition, in the presence of silicon carbide, when the nanoparticles’ content was increased, the undulation of average peeling force values decreased at a constant thickness reduction. Finally, it was found that the bond strength of IF steel strips was less than that of aluminum and copper strips. This was attributed to their crystal structure.     

Microstructure and superplasticity of AZ31 sheet fabricated by differential speed rolling

Microstructure evolution and superplasticity in AZ31 alloy by differential speed rolling (DSR) with a high-speed ratio (=3) between the upper and lower rolls was examined. With increase in thickness reduction by DSR at 473 K, degree of grain refinement and microstructure homogeneity increased. The microstructure obtained by a single rolling pass for a 70% reduction in thickness consisted of recrystallized grains with a mean size of 2 μm, and fraction of HAGBs and average misorientation angle determined by the EBSD analysis were 0.47 and 23.21°, respectively. The DSR AZ31 alloy exhibited enhanced superplasticity as compared with the conventionally processed AZ31. A maximum elongation of 830% was obtained at 2 × 10⁻⁴ s⁻¹ and 673 K. The strain hardening exponent measured at 2 × 10⁻⁴ s⁻¹ and 673 K was as high as 0.71, which could be related to accelerated grain growth in the highly refined microstructure during superplastic flow.     

加磷高强IF钢的最优冷轧压下率确定

为了确定加磷高强IF钢的最优冷轧压下率,以工业生产的加磷高强IF钢热轧钢板为试验材料,在实验室进行了冷轧试验和盐浴退火试验,研究了冷轧压下率对试验钢显微组织和力学性能的影响。结果表明：在试验条件下,试验钢冷轧压下率为50%～80%,退火温度为820～850℃时,再结晶完成;随着冷轧压下率的增加,晶粒变得细小均匀;冷轧压下率为50%～80%,退火温度为850℃时,屈服强度为160 MPa左右,抗拉强度为345 MPa左右,延伸率为35.0%左右,塑性应变比r值和应变硬化指数n值都较高,r值为1.5左右,n值为0.30左右。最终确定工业生产中最优冷轧压下率为60%～70%。     

S390粉末高速钢高温变形流动应力行为与预测

在变形温度为950～1200℃、应变速率为0.002～1 s^-1和变形程度为50%的条件下,采用Gleeble-1500D热模拟机进行S390粉末高速钢等温压缩实验,研究其热变形行为。S390粉末高速钢的流动应力随着变形温度的降低和应变速率的升高而显著增大,可通过Zener-Hollomon参数综合反映。通过实验测定的数据,建立了基于双曲正弦Arrhenius方程的综合性本构模型。考虑变形程度对S390粉末高速钢变形行为的影响,材料常数如α、n、ln A、Q等均为应变的函数。所建立本构方程的流动应力预测值与实验值吻合较好,平均相对误差为5.055%,表明该本构方程用于分析S390粉末高速钢的热变形行为是可靠的。     

半高速钢轧辊材料性能的研究

通过正交试验设计了半高速钢轧辊的化学成分，性能测试结果表明，半高速钢材料的耐磨性约为贝氏体球墨铸铁材料的2倍，并研究分析了钒、钼、钨、碳对半高速钢轧辊组织和性能的影响。     

异步轧制AZ31镁合金板材室温冲压性能研究

文章主要对异步轧制AZ31镁合金板材室温冲压性能进行了研究,以探讨提高镁合金板材冲压性能的途径。结果表明,异步轧制有利于板材的晶粒细化,其晶粒尺寸约为7.6μm,明显小于普通轧制板材的12.5μm;而由于异步轧制过程中剪切变形的作用,异步轧制使板材的(0002)基面晶粒取向减弱;与普通轧制相比,异步轧制板材的应变硬化能力增加,屈服强度降低,制耳参数减小,但塑性应变比也降低,这可归因于异步轧制所导致的晶粒细化和晶粒取向的改变。     

热轧不锈钢板带粗轧机架高速钢轧辊的研制

由于不锈钢热轧板带产线粗轧温度高、压下量大、轧辊咬入角大、辊面受挤压力和摩擦力更大等工况特点,原轧辊材质的应用受到了限制。介绍了热轧不锈钢板带粗轧新型高速钢轧辊的研制情况,主要介绍了其化学成分、热处理工艺、内层材质的设计及其组织性能。该新型高速钢轧辊在国内某1 780 mm不锈钢热轧产线粗轧机组的应用取得了较好效果,毫米轧制量为7 000 t/mm,下机辊表面光洁,表面粗糙度为1.3～1.6 μm。