循环扩挤变形AZ80镁合金的组织、织构与力学性能

采用循环扩挤(Cyclic expansion-extrusion,CEE)变形工艺对AZ80镁合金的块状材料进行热挤压加工,观察试样的微观组织与织构,并测试了力学性能。结果表明:AZ80镁合金经过CEE变形后,晶粒的尺寸明显细化,第4道次CEE变形之后,晶粒尺寸从150~230 μm细化至2 μm,整体分布均匀且呈等轴晶;2道次变形后,随着挤压道次的增加,晶粒的细化程度减慢;同时经过CEE变形的AZ80镁合金织构包括了(0001)基面平行于挤压方向与(1120)棱柱面垂直于挤压方向的两种不同纤维织构,随着挤压道次的增加,织构总体强度出现先减后增再减的变化;力学性能相对于均匀化态有着明显的变化,第1道次CEE变形之后,抗拉强度与屈服强度分别达到各自的最大值,为290 MPa和180 MPa,第2道次CEE变形之后,强度出现不随晶粒细化而增强的现象(反Hall-Petch理论),这是因为织构的软化作用强于晶粒的细化作用,而伸长率随着挤压道次的增加而提高。     

ECAP变形对20MnSi钢组织与性能的影响

采用C方式等径弯曲通道变形(Equal Channel Angular Pressing,简称ECAP)对20MnSi钢进行了4道次室温变形,研究了变形道次对显微组织和力学性能的影响.结果表明,铁素体组织随变形道次的增加逐渐演变为等轴状大角度晶界的亚微晶组织;试验用钢的硬度和强度随变形道次的增加而增加,4道次后强度有所降低;在本试验条件下,珠光体组织中的片状渗碳体表现出很强的塑性变形能力.     

ECAP变形对Mg2Si增强耐热镁合金组织及性能的影响

为了提高镁合金的耐热性能,在Mg-Zn合金中加入Si,形成Mg-Zn-Si镁合金.采用ECAP工艺在变形温度为573 K和挤压路径为Bc条件下对Mg-Zn-Si镁合金进行不同道次的变形.运用金相显微镜(OM)、X射线衍射仪(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)等手段对变形后的Mg-Zn-Si镁合金进行了组织表征,对变形后的合金进行了室温拉伸和高温蠕变等力学性能测试.结果表明:随着挤压道次增加,α-Mg基体、Mg Zn相及Mg2Si相均得到细化且分布趋于均匀.1道次挤压后部分基体α-Mg细化,4道次挤压后α-Mg的尺寸减小为5~10μm,且晶粒大小趋于均匀;2道次挤压后Mg2Si相枝晶在原位置破碎为颗粒状,6、8道次挤压后Mg_2Si相呈弥散分布.4道次挤压后合金的屈服强度和抗拉强度均提高120%,伸长率提高353%;8道次挤压后合金的抗拉强度和伸长率与4道次相比变化不大,但屈服强度进一步提高了19%.随着挤压道次增加,高温抗蠕变性能提高,8道次后高温稳态蠕变速率降低5倍.Mg2Si相细化机理为受剪切而机械碎断.     

铸态ZK60 镁合金往复挤压的组织与性能

目的探索工艺参数对微观组织和力学性能的影响。方法材料选用铸态ZK60合金,通过试验研究挤压比、往复挤压道次对镁合金微观组织演变的影响,分析挤压比对T6处理的材料力学性能的影响。结果在一定范围内增大挤压比和增加往复挤压道次均有助于组织细化。在350℃、挤压比为8时,经过8道次往复挤压变形可以细化晶粒到3μm左右。晶粒尺寸达到5μm以下,增加往复道次使晶粒细化的效果不明显,但有利于晶粒的均匀化。在往复挤压温度350℃,挤压比8,往复道次8的条件下,经过T6处理的试样具有良好的综合力学性能,伸长率达到22.1%,抗拉强度为308.6 MPa。结论 ZK60镁合金在往复挤压和动态再结晶过程中,晶粒的细化与往复挤压道次和挤压比有关。若挤压比较小,尽管往复道次较大,但是晶粒细化的效果不明显;合理的匹配挤压比与往复道次,能获得细小、均匀的组织。     

等径角挤扭工艺的研究

针对等径角挤压(ECAP)工艺和挤扭(TE)工艺中,材料变形不均匀,1道次变形获得的应变量不够大的缺点,将2种工艺有机结合,提出了等径角挤扭(ECAPT)工艺。利用UG和DEFORM-3D软件进行几何造型和有限元模拟,研究变形过程、应力应变分布和载荷变化,并用纯铝进行2道次ECAPT实验,测量试样显微组织和力学性能的变化。结果表明,ECAPT使组织产生更大的应变量,随着行程的增加,载荷增大,在TE通道平稳阶段达最大值,试样头部挤出TE通道后载荷降低;材料的宏观形貌同模拟结果一致,显微组织发生了明显细化,其中第1道次z面和第2道次y面细化效果明显;力学性能得以较大提高,屈服强度由43.31MPa提升至52.19MPa,抗拉强度由71.30MPa提升至130.38MPa。     

异步累积叠轧纯铜材的取向变化过程与力学性能

室温下对纯铜薄板进行一到六道次的异步累积叠轧变形加工。采用金相显微镜、扫描电镜附带背散射电子衍射、X射线衍射仪附带织构附件及拉伸试验机进行组织、取向观察及力学性能测试,获得铜材异步叠轧过程的显微组织、轧制织构变化过程和力学性能。结果表明:经过六道次的异步累积叠轧变形,由于压缩变形与剪切变形作用,使晶粒细化,铜材晶粒尺寸由30～50μm细化到5μm。异步叠轧过程中出现:{112}〈111〉,{123}〈634〉,{011}〈211〉和{011}〈100〉几种主要组分轧制织构。材料的屈服强度与抗拉强度明显提高,六道次后分别达到348MPa和452MPa。材料的伸长率在二道次后显著下降到2.3%,然后随等效应变的增加略微下降。     

异步累积叠轧纯铜材的取向变化过程与力学性能EI北大核心CSCD

室温下对纯铜薄板进行一到六道次的异步累积叠轧变形加工。采用金相显微镜、扫描电镜附带背散射电子衍射、X射线衍射仪附带织构附件及拉伸试验机进行组织、取向观察及力学性能测试,获得铜材异步叠轧过程的显微组织、轧制织构变化过程和力学性能。结果表明:经过六道次的异步累积叠轧变形,由于压缩变形与剪切变形作用,使晶粒细化,铜材晶粒尺寸由30～50μm细化到5μm。异步叠轧过程中出现:{112}〈111〉,{123}〈634〉,{011}〈211〉和{011}〈100〉几种主要组分轧制织构。材料的屈服强度与抗拉强度明显提高,六道次后分别达到348MPa和452MPa。材料的伸长率在二道次后显著下降到2.3%,然后随等效应变的增加略微下降。     

室温多向压缩道次变形量对AZ80镁合金力学性能影响

目的 探明室温塑性变形对AZ80塑性、硬度及最大应力等力学性能的影响规律,为其成形工艺参数制定提供依据。方法 对挤压态AZ80镁合金均匀化处理后,在室温下控制道次变形量(0.05、0.075、0.1)及累积应变进行多向多道次压缩变形;利用力学试验机和维氏硬度计分析道次变形量与累积应变对其力学性能的影响。结果 在室温下,当AZ80镁合金单向压缩的真应变达到0.124时会发生开裂,通过小应变多向多道次压缩可以将累积应变至少提高至3.6以上。在道次变形量为0.05、0.075和0.1时,累积应变分别可达到7.5、6和3.7;在累积应变为3.6时,随着道次变形量的增加试样硬度(HV)分别达到94、110和121,较未变形试样硬度(70HV)分别提升了33%、57%和73%。结论 AZ80镁合金通过室温多向多道次压缩有利于改善材料塑性,提高力学性能。其塑性随着道次变形量的减小而提高,硬度和最大应力随道次变形量和累积应变的增加而升高,且道次变形量比累积应变对硬度和最大应力的影响更大。     

等径角挤压过程中材料的流变行为研究

分析了等径角挤压过程中材料流变的原因和特征,认为每道次挤压材料内部发生的剪切变形量与时间的函数曲线呈近似正态分布,适当升高温度和增加背压能有效减小难变形区,降低通道与试样接触面之间的摩擦能减小材料内部的滞变区.通过实验证明,随着挤压道次的增加,材料内部的滞变区将减小,均匀化程度会逐步提高.     

往复挤压高韧Mg-Zn-Y合金

将铸态Mg92.5Zn6.4Y1.1镁合金往复挤压2,4,8,12不同道次,然后分别正挤压制成φ12mm的棒材.采用OM,XRD及DTA研究了往复挤压不同道次镁合金的组织和力学性能.研究表明,铸态Mg92.5Zn6.4Y1.1镁合金往复挤压后,组织得到显著细化,力学性能得到大幅度提高,获得了高强韧镁合金.2道次后,晶粒约5μm,拉伸强度超过300MPa,伸长率高达20%.继续增加往复挤压道次,晶粒细化和拉伸性能提高均不明显,当往复挤压12道次时,拉伸强度明显降低,而伸长率达到23%.Mg92.5Zn6.4Y1.1镁合金的伸长率大幅度提高归因于在往复挤压过程中,铸态组织中的缩松、缩孔等缺陷闭合和成分偏析非均匀相的分布均匀化,以及晶粒的破碎、回复和动态再结晶所引起的晶粒细化及材料的流动,最终获得完全致密、细小而均匀的等轴晶组织.     

Mechanical properties of a two-phase alloy Mg–8%Li–1%Al processed by equal channel angular pressing

The microstructural evolution and room temperature tensile properties of Mg–8%Li–1%Al alloy processed by equal channel angular pressing (ECAP) at 403 K were investigated. It was found that the strength could be improved pass by pass. The elongation-to-failure decreased dramatically after the first ECAP pass, but could be improved pass by pass during the subsequent ECAP procedure. The microstructure analysis gave the explanations for these phenomena.     

Coupling kinetic dislocation model and Monte Carlo algorithm for recrystallized microstructure modeling of severely deformed copper

By coupling a kinetic dislocation model and Monte Carlo algorithm, the recrystallized microstructure of severely deformed Oxygen Free High Conductivity Copper (OFHC) is predicted at different strains imposed by Equal-Channel-Angular-Pressing (ECAP) and annealing temperatures. From a flow field model, the strain rate distribution during the ECAP of the material in a curved die is calculated. Then using the kinetic dislocation model, the total dislocation density and correspondingly the stored energy after each ECAP pass is estimated. Utilizing the Monte Carlo algorithm and the stored energy, the recrystallized microstructure is predicted. The results show that the recrystallized grain size is decreased rapidly from the strain of first to fourth pass and then it is decreased slowly. Also, it is achieved that with increasing the annealing temperature, the grain size is increased. Moreover, a good agreement is observed between the predicted results and experimental data.     

Effect of initial microstructure on the processing of titanium using equal channel angular pressing

Equal channel angular pressing (ECAP) is a metal processing technique that is used to produce materials with ultrafine (<1 μm) grain sizes. In this work, the effect of the initial microstructure on ECAP of commercially pure titanium (CP Ti), a material used in many industrial applications, was investigated. To produce different initial microstructures, samples of CP Ti were exposed to different annealing conditions: no annealing (Material 1), annealed at 1033 K for 2 hr (Material 2), or annealed at 1173 K for 4 hr (Material 3). Each material was subjected to one pass of ECAP and the resulting microstructures were analyzed using XRD, SEM, and TEM, and compared to the microstructures before ECAP. It was found that each material developed a unique microstructure after one pass of ECAP, which was attributed to the varying microstructural characteristics before ECAP. Microhardness values before and after ECAP varied with each microstructure.     

Precipitation hardening and grain refinement in an Al–4.2wt%Mg–1.2wt%Cu processed by ECAP

The precipitation and the strength evolution during equal channel angular pressing performed at 180 °C in an Al–4.2wt% Mg–1.2wt%Cu alloy have been studied by room temperature compression tests and transmission electron microscopy. The age hardening behaviour of these AlMgCu alloys, in which the precipitation sequence involves the S-phase and its precursors, was investigated and revealed a yield strength peak after 8 days at 180 °C. The influence of the Severe Plastic Deformation on the microstructure and mechanical properties of under-aged and peak-aged samples are presented. Notably, in the under-aged sample, a gradual increase of the strength after each ECAP pass is obtained while, the peak-aged samples loose much of their strength during the first ECAP pass. TEM characterization of the microstructure before and after ECAP is presented and linked to the evolution of the mechanical properties.     

High Strength AA7050 Al alloy processed by ECAP: Microstructure and mechanical properties

Commercial AA7050 aluminium alloy in the solution heat-treated condition was processed by ECAP through routes A and B_C. Samples were processed in both room temperature and 150 °C, with 1, 3, and 6 passes. The resulting microstructure was evaluated by optical microscopy (OM) and transmission electron microscopy (TEM). Only one pass was possible at room temperature due to the low ductility of the alloy under this condition. In all cases, the microstructure was refined by the formation of deformation bands, with dislocation cells and subgrains inside these bands. The increase of the ECAP temperature led to the formation of more defined subgrain boundaries and intense precipitation of spherical-like particles, identified as η′ and η phases. After the first pass, an increase in the hardness was observed, when compared with the initial condition. After 3 passes the hardness reached a maximum value, higher than the values typically observed for this alloy in the overaged condition. The samples processed by route B_C evolved to a more refined microstructure. ECAP also resulted in significant strength improvement, compared to the alloy in the commercial overaged condition.     

等通道挤压AZ80镁合金的析出行为和性能

研究了AZ80镁合金经300℃等通道挤压(ECAP)后的组织、织构与力学性能的演变规律以及第二相析出行为的影响。结果表明:ECAP显著促进了粒状连续析出,可有效节省后续热处理时间。A路径多道次挤压最终获得基面织构;Bc路径挤压后形成基面近似平行于剪切面的织构;第二相析出对ECAP织构特征的形成没有显著影响。用该工艺可获得较高的延伸率(13%-19%),但是抗拉强度过低(300 MPa),综合机械性能不理想。可通过抑制挤压前的未溶粗大粒子的析出、减少挤压道次和降低挤压温度等措施优化AZ80的析出控制。     

Mechanical properties,microstructure and texture of single pass equal channel angular pressed 1050, 5083, 6082 and 7010 aluminum alloys with different dies

Four important commercial aluminum alloys, namely 1050, 5083, 6082 and 7010AA are processed through a single pass via two equal channel angular pressing (ECAP) dies with different geometries (die angles of 90° and 120°). Electron back scattered diffraction (EBSD) is applied on the flow plane of the processed samples. Large scans with a step size of 7 μm for grain size distribution and texture measurements, as well as small scans with a step size of 0.1 μm for determination of cell size distribution, were performed. Hardness and simple compression are employed to evaluate the mechanical properties of the ECAP processed samples. Shear bands in the ECAP processed 7010AA was a major feature that led to failure in all samples subjected to further simple compression. The hardness as well as the stress–strain behavior was similar in the ECAP processed 6082 and 5083AA. The die geometry and the strain involved in the single pass influenced the overall texture intensity developed in the wrought alloys (1050 and 5083AA) and had minimal influence on the texture intensity of the heat treatable alloys (6082 and 7010AA). Low angle grain boundaries dominated the microstructure of all alloys for all testing conditions.     

Effect of Creep and Aging on the Precipitation Kinetics of an Al–Cu Alloy after One Pass of ECAP

Recent work shows that severe plastic deformation processes such as ECAP or HPT considerably accelerate the precipitation kinetics of Al‐Cu alloys. In this study, the authors analyze how a combination of mechanical load, aging time (and increased plastic strain), and aging temperature affects the precipitation kinetics of an AA2017 alloy after ECAP. After solution annealing, the material is processed by one pass of ECAP (120°‐channel angle) at 140 °C. Compressive creep tests are performed on the initial condition and the ECAP‐deformed material. The resulting microstructures are studied in detail using electron microscopy. To investigate the influence of mechanical loading, interrupted compressive creep tests are performed and compared with aged samples (produced without any mechanical loading at the same temperature and after the same amount of time). By keeping time and load constant in another set of interrupted compressive creep tests, the influence of temperature is investigated. Our study shows that increasing mechanical loading further accelerates the precipitation kinetics. Temperature accelerates the precipitation kinetics as well, but results in coarser precipitates. The authors also find that different creep strains can lead to the formation of two different regions in the microstructure: regions with only a few coarsened θ‐phase precipitates, and regions with numerous, finely dispersed precipitates.