等通道转角挤压铝硅合金组织的研究

研究了铝硅合金等通道转角挤压后组织变化,铝硅合金在等通道转角挤压过程中由于剪切力的作用细化了硅晶粒,改善了材料的性能,实验证明：等通道转角挤压技术是细化晶粒的新方法。     

等通道转角挤压——提高材料性能的有效方法

等通道转角挤压法是能使块体材料得到超细晶粒的一种新的材料加工方法，目前受到材料研究者的广泛关注。简要介绍等通道转角挤压法(ECAE)的基本原理及通过该方法得到的有效应变量的主要影响因素。综述等通道转角挤压法研究和应用现状，同时展望该方法的应用前景。     

等通道转角挤压超细晶材料技术及其发展

通过金属的大塑性应变细化晶粒从而提高材料综合性能已在材料加工领域得到广泛应用。近年来为获得材料的亚晶组织已经出现了许多大变形技术。等通道转角挤压(ECAP)是块体材料得到超细晶粒的一种新的材料加工方法,因此受到材料研究者的广泛关注。介绍了等通道转角挤压的基本原理以及主要参数对变形的影响,分析了此加工方法对材料组织与性能的影响,讨论了其在材料加工研究中的应用。     

等通道转角挤压工艺对5083铝合金超声空蚀行为的影响

对5083铝合金进行等通道转角挤压(ECAP)加工,利用超声空蚀设备对ECAP加工前后的5083铝合金试样进行超声空蚀实验,研究了ECAP加工对5083铝合金空蚀行为的影响.结果表明：经ECAP加工后,5083铝合金的平均晶粒尺寸明显减小,硬度也有一定的提升;抗空蚀系数由1.651 h/mm增至2.087 h/mm,提升了约26%,空蚀累计最大质量损失由64.2 mg下降至50.8 mg.结合最大空蚀坑深度和平均空蚀坑深度变化可知,ECAP使5083铝合金发生了加工硬化和强化,以及晶粒细化和第二相弥散分布,从而提升了材料的抗空蚀能力.     

不同方式等通道转角挤压纯铝微结构分析

等通道转角挤压技术是制备超细晶粒金属块材的最新技术方法。文章介绍了通过实验对纯铝A、B、C三种方式挤压,A方式:每次挤压试样方位不变,在同一方向上承受累积剪切变形;B方式:不同道次挤压时,试样沿挤压轴线相同方向旋转90°,使主剪切平面保持垂直;C方式:在相邻挤压道次之间,试样沿挤压轴线相同方向旋转180°,使偶次挤压后,主剪切平面的累积剪切应力趋于零。经实验观察表明,A、B两种方式挤压后,微结构变化基本相同,晶粒沿剪切方向拉长,4次挤压后晶粒形状和分布有了差别。而C方式与A、B的不同在于偶道次挤压后晶粒形状为等轴晶粒。三种方式后的硬度与挤压道次的关系基本一致,即3～4次挤压后硬度趋于饱和。实验证明,经不同方式等通道转角挤压(ECAE)纯铝组织结构变化有所不同。     

镁及镁合金剧烈塑性变形研究及发展趋势

本文介绍了主要的剧烈塑性变形方法,对镁合金等通道转角挤压、高压扭转、搅拌摩擦加工和多向锻造等剧烈塑性变形的研究现状进行了综述,比较了几种剧烈塑性变形方法的特点,并提出了未来镁合金剧烈塑性变形技术的发展方向.     

镁及镁合金挤压模具的设计特点

论述了镁及镁合金挤压工模具的特点及与铝及铝合金挤压工模具的异同,分别介绍了镁及镁合金棒材模、无缝管材模、型材模及平面组合模的设计要点并举例说明,对指导生产实践有一定的价值。     

镁及镁合金晶粒细化的研究现状

叙述了镁及镁合金晶粒细化的几种方法，即合金化法、变质处理法、固态变形处理法、半固态成形法、快速凝固法及熔体搅拌法等。细化镁合金晶粒尺寸能显著提高其力学性能．这对推广镁合金的应用具有重要意义。     

镁及镁合金型材的挤压

在镁及镁合金加工材中，挤压材占着重要的地位，从普通的管材到核工业的燃料盒，品种与规格不下五千种。虽然全球2002年挤压材的产量还不到3000t，但用途却很重要。本文对挤压用镁合金及其挤压材的性能及生产工艺作了扼要的介绍。     

等通道转角挤压组织演变规律的研究进展

综述了金属结构材料和功能材料基体相晶体结构、层错能、Hollomon参数lnZ对等通道转角挤压ECAP变形组织演变规律影响的研究进展,试样基体相的晶体结构对变形组织的演变起重要的影响作用。随着应变量的增大,密排六方结构金属先形成形变孪晶、再启动优先存在的但被阻塞的滑移系统;面心立方结构金属的位错滑移主导着组织演变与晶粒细化过程,先形成亚晶界,再增大组织取向差,最终形成大角度晶界。在高层错能材料中,随着Hollomon参数lnZ增大,位错运动受到抑制,驱使变形机制从位错滑移逐渐转变成形变孪晶;当Z参数减小时,在ECAP高层错能材料中会形成微尺度的剪切带。在低层错能材料中形成丰富的孪晶,极低层错能的材料形成宏观剪切带。而中等层错能材料的变形机制则取决于Z值的高低。分析了ECAP过程动态再结晶的影响因素,认为γm·ln2Z30不宜作为ECAP过程是否发生动态再结晶的判据,ECAP过程动态再结晶的影响因素还有待进一步研究,如弄清ECAP过程温升规律、分析淬火保存ECAP变形组织将有助于研究ECAP动态再结晶。     

Microstructure evolution in Zr under equal channel angular pressing

Pure polycrystalline Zr was deformed by equal channel angular pressing (ECAP), and the microstructural characteristics were analyzed. By repeated alternating ECAP, it was possible to, refine the grain size from 200 to 0.2 μm. Subsequent annealing heat treatment at 550°C resulted in a grain growth of up to 6 μm. Mechanical twinning was an important deformation mechanism, particularly during the early stage of deformation. The most active twinning system was identified as 85.2 deg tensile twinning, followed by 57.1 deg compressive twinning. Crystal texture as well as grain-boundary misorientation distribution of deformed Zr were analyzed by X-ray diffraction (XRD) and electron backscattered diffraction (EBSD). The ECAP-deformed Zr showed a considerable difference in the crystallographic attributes from those of cold-rolled Zr or Ti, in that texture and boundary misorientation-angle distribution tend toward more even distribution with a slightly preferential distribution of boundaries of a 20 to 30 deg misorientation angle. Furthermore, unlike the case of cold rolling, the crystal texture was not greatly altered by subsequent annealing heat treatment. Overall, the present work suggests ECAP as a viable method to obtain significant grain refining in hexagonal close-packed (hcp) metals. This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals and Alloys” at the TMS Annual Meeting, February, 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee.     

Microstructure evolution in Zr under equal channel angular pressing

Pure polycrystalline Zr was deformed by equal channel angular pressing (ECAP), and the microstructural characteristics were analyzed. By repeated alternating ECAP, it was possible to refine the grain size from 200 to 0.2 μm. Subsequent annealing heat treatment at 550 °C resulted in a grain growth of up to 6 μm. Mechanical twinning was an important deformation mechanism, particularly during the early stage of deformation. The most active twinning system was identified as 85.2 deg {10 2}〈 011〉 tensile twinning, followed by 57.1 deg {10 1}〈 012〉 compressive twinning. Crystal texture as well as grain-boundary misorientation distribution of deformed Zr were analyzed by X-ray diffraction (XRD) and electron backscattered diffraction (EBSD). The ECAP-deformed Zr showed a considerable difference in the crystallographic attributes from those of cold-rolled Zr or Ti, in that texture and boundary misorientation-angle distribution tend toward more even distribution with a slightly preferential distribution of boundaries of a 20 to 30 deg misorientation angle. Furthermore, unlike the case of cold rolling, the crystal texture was not greatly altered by subsequent annealing heat treatment. Overall, the present work suggests ECAP as a viable method to obtain significant grain refining in hexagonal close-packed (hcp) metals. This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee.     

纯铝等径角挤压塑性流动的有限元模拟分析

本文采用DEFORM有限元软件模拟分析了ECAP过程中纯铝的塑性流动.通过模拟分析得出,可将ECAP过程中挤压力的变化分成四个阶段:A区:挤压起始阶段挤压力很低,随后挤压力接近线性增加;B区:挤压力先增加后减小,其中增加速率比A区缓慢;C区:挤压力基本趋于稳定;D区:随着挤压的进行挤压力开始回升.挤压过程中材料塑性流动的均匀部分大致可分为三个区域:内侧A区,变形体延伸方向与水平方向的夹角约为27.5(°);中间B区,变形体延伸方向与水平方向的夹角约为28.6(°);外侧C区,变形体延伸方向与水平方向的夹角约为56.6(°).同时,通过理论计算得到了变形体延伸方向与水平方向的夹角.结果表明:模拟结果与理论计算相符.     

等径角挤扭法制备SiC_p/Al复合材料的界面特性

以Al和SiC的混合粉末为原料,采用等径角挤扭工艺制备出含Si C颗粒(体积分数8.75%)的SiCp/Al复合材料,并对其界面情况进行研究。采用X射线光电子能谱(XPS)对制备出的复合材料界面结合处的Si和Al元素的价态进行测定,利用扫描电镜(SEM)和场发射扫描电镜(FE-SEM)观察结合界面。结果表明,SiC的氧化层与Al之间形成了冶金结合界面过渡层,材料界面处的显微硬度从1.73 GPa过渡到0.64 GPa,冶金结合界面使材料表现出优良的耐蚀性,材料的压缩断口界面层为塑性断裂。     

超细晶材料制备新工艺——等径角挤压

综述了等径角挤压制备超细晶材料领域的最新研究进展,包括等径角挤压的工艺原理、显微组织演化规律、等径角挤压材料微观组织特征和力学性能等.     

等径角挤压工艺路径对铝粉烧结体微观组织的影响

采用金相电子显微镜、透射电镜观察及有限元模拟等分析手段,研究了等径角挤压工艺路径(A、BC和C路径)对铝粉烧结体微观组织和晶粒细化效果的影响。结果表明:BC路径变形后试样组织均匀性好,晶粒细化效果明显。其组织内部位错滑移的产生,除了受材料晶体结构特征的影响,多道次累积变形过程中剪切外力与晶粒间的取向关系也是关键所在。在等径角挤压强烈的剪切作用下,初始无序分布的晶粒会呈现单一的取向性,当多道次累积变形相邻道次剪切面夹角接近金属滑移系易于开动的软取向时,组织内部的位错滑移增加。     

The microstructural evolution during the equal channel angular pressing process and its relationship with the tensile behavior of oxygen-free copper

In the present study, the tensile behavior of nanograin-sized, pure copper produced by the equal channel angular pressing (ECAP) process, which is at present one of the most popular methods for producing nanograined bulk material, was examined as related to the microstructural evolution. It was found that the yield and tensile strength values of 99.99 pct pure, oxygen-free copper increased with the increasing number of ECAP cycles due to the strain hardening in the initial stage. Further ECAP process promoted the formation of equiaxed grains accompanied with the gradual decrease in dislocation density. Once the equiaxed grain formed, the decrease in dislocation density would be further accelerated due to the extremely high rate of dynamic recovery with the grain boundary area acting as a dislocation sink. The strain hardening mechanism would then stop to operate and the fine grain boundary hardening mechanism would begin to dominate after the forth cycle of the ECAP process, resulting in an increase in the tensile ductility without sacrificing the strength. This research was supported by Grant No. 03K1501-00310 from the Center for Nanostructured Materials Technology under the 21st Century Frontier R&D Programs of the Ministry of Science and Technology, Korea.     

退火温度对20MnSi钢ECAP变形组织的影响

采用C方式等径弯曲通道变形（ECAP）法制备了平均晶粒尺寸-0.20 μm的亚微晶20MnSi钢,研究了退火温度对ECAP变形组织的影响.结果表明,随退火温度升高,ECAP变形获得的亚微晶铁素体变形组织在原位逐渐演变为再结晶组织,300～500℃退火1 h后,亚微晶铁素体组织稳定,晶粒无明显长大.退火温度高于500℃后,铁素体晶粒开始明显长大,650℃退火后的铁素体平均晶粒尺寸-8μm.经ECAP变形的珠光体组织在较低温度退火时,渗碳体具有较强的球化能力.     

纯钛粉末室温单道次等径角挤压变形行为

应用Deform-3D V6.1软件,对室温下纯钛的等径角挤压(ECAP)过程进行有限元模拟,研究试样的等效应变分布情况;并采用两通道夹角φ=90°、外圆角ψ=60°的模具,在室温下实现粉末烧结纯钛单道次ECAP变形,研究挤压后试样不同部位的显微组织和性能,以及等径角挤压对粉末烧结纯钛致密化的影响.模拟结果表明:变形主...