5052铝合金表面晶粒超细化后腐蚀性能研究

对表面晶粒超细化和未经表面超细化处理的5052铝合金的样品分别进行仿海水腐蚀对比实验,在3.5%NaCl+0.05%MgCl2(原子分数)水溶液中分别测出不同表面晶粒尺寸的腐蚀速率。结果表明,5052铝合金表面晶粒超细化后抗蚀性能提高,其平均腐蚀速率与表面晶粒尺寸呈线性关系。     

AZ31镁合金晶粒细化方法及机制研究现状

系统介绍了AZ31镁合金晶粒细化方法及机制,综述了6种制备细晶镁合金大塑性变形方法的工艺特点和应用,展示了大塑性变形方法在AZ31镁合金加工中的应用前景。     

铝合金晶粒细化方法的研究现状及最新动向

综述了铝合金晶粒细化的各种方法与应用现状，分析了各种细化方法的细化机理。并对新型中间合金细化剂如Al-Ti-B-RE、Al-Ti-C-RE等的细化效果进行讨论，最后阐述了一种新的晶粒细化方法一细晶铝锭及其对铝合金的细化效果、细化机理及应用。     

塑性变形中晶粒变形与细化机制的影响因素

讨论了层错能、应变速率和变形温度等因素在塑性变形制备超细晶/纳米晶材料的变形过程中,对变形机制与晶粒细化机制的影响.研究表明,随着层错能的降低,晶粒的变形机制会由位错滑移向机械孪生转变,有利于晶粒的细化.应变速率的增加与变形温度的降低有利于抑制位错动态回复、增加流变应力,促使晶粒进一步细化.     

7475铝合金ECAP的晶粒细化极限

将等径弯曲通道变形应用于7475铝合金,等效真应变达12.对7475铝合金在不同温度下ECAP变形后显微组织特征和晶粒细化极限进行了研究.结果表明:变形温度从273 K到773 K,7475铝合金的晶粒细化极限为0.29～1.90 pm,且极限晶粒尺寸的倒数与变形温度的倒数成正比关系.在较高温度下,组织中产生大量的沉淀相粒子能有效钉扎晶界,阻碍晶粒长大,使合金具有较好的组织热稳定性.     

铝合金晶粒细化剂的发展趋势

综述近些年来铝合金晶粒细化剂的研究与应用状况。对Al-Ti、Al-Ti-B、Al-Ti-C、Al-Ti-C-B、Al-Ti-B-RE等晶粒细化剂进行了比较,并对具有代表性的细化理论如包晶反应、碳化物一硼化物及组织遗传性进行丁分析和讨论。认为添加了具有特殊性质稀土的Al-Ti-C-RE和Al-Ti-C-B-RE的多元合金晶粒细化剂是今后发展的方向。     

铝晶粒细化机制的研究进展

系统论述了铝工业中常用的Al-Ti、Al-B、Al-Ti-B(Ti/B＞2.22)、Al-Ti-B(Ti/B＜2.22)、Al-Ti-C等5大系列细化剂的细化机制,包括包晶理论、共晶理论、三元包晶理论、三元共晶理论、"碳化物-硼化物粒子"理论、"TiC粒子团"理论、包晶"残骸"(hulk)理论、超形核(Hypernucleation)理论、双重形核机制("duplex" nucleation mechanism)和复杂共晶机制等,分析了各种机制的科学性和局限性.     

7050铝合金晶粒细化的研究

在普通连铸以及电磁连铸下制备了加入和不加细化剂Al-Ti-B的7050铝合金,研究了Al-Ti-B以及电磁场对合金晶粒细化的影响,结果显示加入0.2%的Al-Ti-B与磁场的引入均可有效的细化晶粒.此外,细化剂在磁场作用下依然可以发挥效用,在磁场与细化剂的共同作用下的晶粒细化效果比二者单独作用下的都要好,铸锭边部与中心晶粒尺寸分别达到70 μm和53 μm.     

压铸铝合金表层晶粒细化的方法研究

传统压铸法生产的高硅铝合金铸件,容易产生表面疏松、微气孔、"铸巢"等缺陷,降低了压铸件的品质,并会对烤漆、电镀等后续加工产生诸如脱漆、起泡等严重影响,限制了高硅铝合金压铸件在高标准外观要求产品领域中的应用.本文通过对大量压铸件中"铸巢"这一缺陷的研究并详细分析压铸工艺过程,发现使用向脱模剂中添加形核剂的方法可以消除"铸巢",同时细化晶粒、减少微气孔、增加铸件细晶层厚度,从而提高铝合金压铸件表层组织的致密度,并起到了提升铸件气密性的作用.     

ECAP法对H62黄铜的晶粒细化研究

通过ECAP（equal channel angular pressing）法对H62黄铜进行了研究.黄铜试样经过ECAP挤压后,在模具通道的转角处发生了剧烈塑性变形,使晶粒不断细化.对挤压后的试样进行显微组织观察、硬度测试、力学性能测试,结果表明ECAP法对H62黄铜的晶粒细化,硬度,强度的提高有显著的作用.     

剧烈塑性变形条件下工业纯钛晶粒细化机理研究

通过对工业纯钛表面机械研磨(SMAT)这种变形方式的结果和微观组织变化的研究,分析了工业纯钛的品粒细化机制,讨论了其他剧烈塑性变形技术无法制备出晶粒尺寸更小的纳米晶的原因.结果表明:对于工业纯钛,SMAT这种具有高的应变速率和多方向载荷的变形方式,有利于形成细小的纳米晶;同时高应变速率增加了位错滑移的临界分切应力.     

Consolidation of AA 7075-2 wt% ZrO_2 Composite Powders by Severe Plastic Deformation via ECAP

The powders of the AA 7075-ZrO_2 were mixed by mechanical milling, but it was found that the system presents a few disadvantages when processed by conventional sintering and hot extrusion, since intermetallic phases between ZrO_2 particles and alloying elements were formed. Equal channel angular pressing(ECAP) processing was proposed as an alternative method to consolidate the composite where there is no intermetallic formation. The analysis of the ECAP process showed that the intermediate temperature(220 ℃) produced a higher consolidation level than conventional sintering and hot extrusion(400 and 500 ℃, respectively). This fact was supported by relative density analysis. In the case of the sintered and hot-extruded sample, the relative density exhibited a value of 0.95, while ECAP sample showed a value of 0.98. Hardness values show that microstructural refinement obtained during mechanical milling was preserved during ECAP processing even when it was carried out at 220 ℃.     

大塑性变形法制备块体纳米材料

综述了大塑性变形法制备块体纳米材料的条件和原理，以及用该法制备的纳米材料的微观结构和力学性能，并分析了其中存在的问题，估计了该技术的实际应用潜力。     

超细晶材料制备新工艺——挤扭

近年对块体超细晶材料的研究已成为材料科学领域一大热点。挤扭工艺作为一种新兴的大塑性变形细晶材料制备技术,在细化材料显微组织、改善材料力学性能、提高材料成形性等方面发挥了重要作用,具有广阔的工业应用前景。文章重点介绍了挤扭工艺的基本原理及其变形特点,综述了国内外挤扭工艺的研究现状和研究进展,指出了该工艺目前存在的问题,并对其应用前景进行了展望,具有较好的实用参考价值。     

基于材料改性的等径角挤压的塑性后处理工艺

简要介绍了等径角挤压成形工艺的特点及目前仍存在的诸多问题,综述了等径角挤压的塑性后处理工艺及其研究进展。传统等径角挤压后再进行其他塑性工艺的后处理,可以有效克服等径角挤压工艺的不足;进一步细化晶粒、增强材料的强度和硬度、改善材料综合性能,是提高等径角挤压制备效率的有效途径。     

室温强塑性变形中铝合金时效析出相的演变

采用硬度测量、透射电镜和X射线衍射等试验方法,探讨了在室温不同强塑性变形下Al-Zn-Mg-Cu、Al-Cu、Al-Mg-Si三种铝合金时效析出相的演变.结果表明,强烈塑性变形能引起绝大部分析出相产生室温回溶,形成过饱和固溶体;每种析出相再溶解的次序不同,先驱相（如GP区、亚稳相）回溶所属的变形程度小于稳定相.     

大塑性变形材料及变形机制研究进展

大塑性变形技术（SPD）具有将铸态粗晶金属的晶粒细化到纳米量级的巨大潜力。综述了SPD技术的分类、优势及其存在问题;介绍了材料在SPD加工过程中的组织转变特点,指出如果超塑性成形能够在镁合金等中得到成功的应用,则可大大拓宽其实际应用领域;描述了SPD细化铝、镁、钛等合金后的微观组织、塑性变形机制与力学性能,最后对大塑性变形技术的应用前景进行了展望。     

Microstructure and mechanical properties of fine grained uranium prepared by ECAP and subsequent intermediate heat treatment

The microstructure and mechanical properties of fine grained uranium prepared by equal channel angular pressing (ECAP) and subsequent intermediate heat treatment were investigated systematically by the confocal laser scanning microscope (CLSM), electron backscatter diffraction (EBSD) and split Hopkinson pressure bar (SHPB). The results show that the initial coarse grained uranium was refined from about 1000 to 6.5 μm prepared by ECAP at 3 passes and subsequent heat treatment, and the corresponding dynamic yield strength increased from 135 to 390 MPa. For the ECAPed uranium samples, the relationship between grain size and yield strength could be described by classical Hall–Petch relationship, and the fitting Hall–Petch relationship for the fine grained uranium samples prepared by ECAP was drawn.     

Using equal-channel angular pressing for the production of superplastic aluminum and magnesium alloys

Equal-channel angular pressing (ECAP) is a useful tool for achieving exceptional grain refinement in bulk metallic alloys. Typically, the grain sizes produced through ECAP are in the submicrometer range, and thus they are smaller by up to an order of magnitude than the grain sizes attained through typical thermomechanical treatments. As a consequence of these ultrafine grains, the as-pressed alloys may exhibit superplastic ductilities at faster strain rates than in conventional superplastic alloys. This work initially describes the application of ECAP to two different alloys. First, results are presented for a commercial Al-2024 alloy where this alloy was selected because it contains no minor additions of either zirconium or scandium to assist in restricting grain growth. The results show that superplasticity is achieved through the use of ECAP. Second, results are described for a Mg-0.6%Zr alloy where this alloy was selected because it is the optimum composition for achieving a high damping capacity. Again, processing by ECAP produces superplastic ductilities not attained in the cast alloy. The second part of this work demonstrates that processing by ECAP may be extended from conventional rod or bar samples to samples in the form of plates. This is a very attractive feature for industrial superplastic forming applications. This paper was presented at the International Symposium on Superplasticity and Superplastic Forming, sponsored by the Manufacturing Critical Sector at the ASM International AeroMat 2004 Conference and Exposition, June 8–9, 2004, in Seattle, WA. The symposium was organized by Daniel G. Sanders, The Boeing Company.     

等通道球形转角挤压过程中工业纯铝的微观组织演变与力学性能

突破传统ECAP变形全过程通道等截面思路,提出一种耦合剪切应变和正应变于一体的新型等通道球形转角挤压(equal channel angular extrusion with spherical cavity,ECAE-SC)工艺。在自行研制的模具上对工业纯铝进行室温单道次ECAE-SC挤压实验,采用OM、EBSD和TEM等技术手段,研究了ECAE-SC变形过程中工业纯铝微观组织的演变规律,并测试了变形后试样的显微硬度。结果表明,在ECAE-SC工艺剧烈简单剪切变形诱导下,工业纯铝仅需1道次挤压变形即可获得等轴、细小、均匀的超细晶组织,平均晶粒尺寸约为400 nm;工业纯铝室温ECAE-SC变形以位错滑移为主并伴有不完全连续动态再结晶,其微观组织经历了剪切带→位错胞→小角度亚晶→大角度等轴晶粒等动态演化过程。1道次ECAE-SC变形后,工业纯铝组织以{110}001高斯织构为主,同时存在部分{111}112铜型织构;材料显微硬度值大幅提升,由初始289.4 MPa提高到565.3 MPa,增幅高达95.33%,且分布均匀性良好。