Simple shear extrusion versus equal channel angular pressing:A comparative study on the microstructure and mechanical properties of an Mg alloy

Two severe plastic deformation(SPD)techniques of simple shear extrusion(SSE)and equal channel angular pressing(ECAP)were employed to process an extruded Mg-6Gd-3Y-1.5Ag(wt%)alloy at 553 K for 1,2,4 and 6 passes.The microstructural evolutions were studied by electron back scattered diffraction(EBSD)analysis and transmission electron microscopy(TEM).The initial grain size of 7.5μm in the extruded alloy was reduced to about 1.3μm after 6 SPD passes.Discontinuous dynamic recrystallization was suggested to be operative in both SSE and ECAP,with also a potential contribution of continuous dynamic recrystallization at the early stages of deformation.The difference in the shear strain paths of the two SPD techniques caused different progression rate of dynamic recrystallization(DRX),so that the alloys processed by ECAP exhibited higher fractions of recrystallization and high angle grain boundaries(HAGBs).It was revealed that crystallographic texture was also significantly influenced by the difference in the strain paths of the two SPD methods,where dissimilar basal plane texture components were obtained.The compression tests,performed along extrusion direction(ED),indicated that the compressive yield stress(CYS)and ultimate compressive strength(UCS)of the alloys after both SEE and ECAP augmented continuously by increasing the number of passes.ECAP-processed alloys had lower values of CYS and UCS compared to their counterparts processed by SSE.This difference in the mechanical responses was attributed to the different configurations of basal planes with respect to the loading direction(ED)of each SPD technique.

Large-scale manufacturing of aluminum alloy plate extruded from subsize billet by new porthole-equal channel angular processing technique

To manufacture plate by the combination of equal channel angular processing （ECAP） and porthole die extrusion techniques, a novel technique, namely portholes-equal channel angular processing （P-ECAP）, was studied. Extrusion of AL6005A plate used for the bullet train plate was investigated by finite element method. The relevant porthole dies involving ECAP technique in channels were designed. Dimensional changes in the scrap part of the extrudate obtained after extrusion from the P-ECAP die, with different channel angles, were predicted. Effects of the channel angle and extrusion speed on the maximum temperature of the workpiece and other field variables were evaluated. At the channel angle of 160° of P-ECAP dies, the extrudate exhibited the optimal performance and the least amount of extrudate scrap was obtained. The optimal extrusion speed was 3-5 mm/s. Moreover, with the increase in ram speed from 1 to 9 mm/s, the peak extrusion load increased by about 49% and the maximum temperature was increased by about 70 ℃. The effective strain exhibited ascending trend in the comer of the ECAP deformation zone. In the solder seam and the side of die bearing of extrudate, the maximum principal stresses were tensile stress.

A new method of characterizing equivalent strain for equal channel angular processing

In order to establish the quantitative relationship between equivalent strain and the performance index of the deformed material within the range of certain passes for equal channel angular processing （ECAP）, a new approach to characterize the equivalent strain was proposed. The results show that there exists better accordance between mechanical property （such as hardness or strength） and equivalent strain after rolling and ECAP in a certain range of deformation amount, and Gauss equation can be satisfied among the equivalent strain and the mechanical properties for ECAP. Through regression analysis on the data of hardness and strength after the deformation, a more generalized expression of equivalent strain for ECAP is proposed as：ε=k0exp[-（k1M-k2）^2], where M is the strength or hardness of the material, k1 is the modified coefficient （k1∈ （0, 1））, ko and k2 are two parameters dependent on the critical strain and mechanical property that reaches saturation state for the material, respectively. In this expression the equivalent strain for ECAP is characterized novelly through the mechanical parameter relating to material property rather than the classical geometry equation.

Microstructure evolution of processed Mg-Al-Zn alloy by equal channel angular extrusion in semi-solid isothermal treatment

Microstructure evolution of processed Mg-Al-Zn alloy by equal channel angularextrusion(ECAE) in semi-solid isothermal treatment was investigated. The results show that withincreasing semi-solid isothermal treatment temperature, the a phase solid grain size of processedMg-Al-Zn alloy by ECAE increases firstly due to coarsening of a phase solid grains, then decreasesdue to melting of a phase solid grains. With the increase of extrusion passes during ECAE, the aphase solid grain size in the following semi-solid isothermal treatment decreases. The a phase solidgrain size of processed Mg-Al-Zn alloy by ECAE under route B_C is the smallest, while the a phasesolid grain size of processed material by ECAE under route A is the largest. The primary mechanismof spheroid formation depends on the melting of recrystallizing boundaries and diffusion of soluteatoms in the semi-solid state.

Mechanical responses, texture and microstructural evolution of high purity aluminum deformed by equal channel angular pressing

Ultrafine-grained(UFG) high purity aluminum exhibits a variety of attractive mechanical properties and special deformation behavior. Equal channel angular pressing(ECAP) process can be used to easily and effectively refine metals. The microstructure and microtexture evolutions and grain boundary characteristics of the high purity aluminum(99.998%) processed by ECAP at room temperature are investigated by means of TEM and EBSD. The results indicate that the shear deformation resistance increases with repeated EACP passes, and equiaxed grains with an average size of 0.9 μm in diameter are formed after five passes. Although the orientations distribution of grains tends to evolve toward random orientations, and microtextures(80°, 35°, 0°),(40°, 75°, 45°) and(0°, 85°, 45°) peak in the sample after five passes. The grain boundaries in UFG aluminum are high-angle geometrically necessary boundaries. It is suggested that the continuous dynamic recrystallization is responsible for the formation of ultrafine grains in high purity aluminum. Microstructure evolution in the high purity aluminum during ECAP is proposed.

不同路径等通道转角挤压镁合金的结构与力学性能

为了研究等通道转角挤压时不同工艺路径对镁合金微观结构及性能的影响 ,采用模角φ =12 0°的模具 ,以A ,BA,BC,C四种工艺路径对AZ31镁合金进行了等通道转角挤压 ,分析测试了室温下挤压试样的微观结构及性能 .结果表明 ,相比于A ,BA,C路径挤压 ,BC 路径挤压容易实现较多的挤压道次和变形量 ;多道次挤压后 ,镁合金的晶粒得到显著细化 ,力学性能也显著改善 ,但不同路径的影响不同 .当挤压 12道次时 ,BC,BA 路径挤压试样的屈服强度显著下降 ,延伸率大幅度提高 ;A ,C路径挤压试样的屈服强度变化较小 ,延伸率的提高幅度也小 .

两步等通道角挤压AZ31镁合金的微观组织和力学性能

对AZ31镁合金经等通道角挤压(ECAE)变形后的微观组织和力学性能进行了研究.结果表明:在498～523 K温度范围内变形后,合金晶粒随着变形程度增加明显细化,延伸率提高,但屈服强度降低;随着变形温度降低,变形后合金的延伸率下降,而屈服强度有所提高.基于以上两点规律提出了两步ECAE工艺,在两步ECAE变形过程中,AZ31合金的变形温度可以降低至453 K,经两步ECAE变形后,获得亚微米级的亚结构AZ31镁合金的强韧性随之得到明显的改善.

Bc路径等径角挤压7090/SiC_p的显微组织及性能

采用Bc路径对超高强铝合金基复合材料7090/SiCp进行等径角挤压加工。采用金相显微镜、力学性能测试及扫描电镜,分析该复合材料的显微组织和力学性能。结果表明:经过4个道次的等径角挤压加工,该复合材料的晶粒逐渐被细化,第三道次后晶粒尺寸达到1μm以下;继续进行等径角挤压时,晶粒未发生明显变化。室温拉伸结果显示:晶粒的抗拉强度逐渐增大,在第三道次下道次间抗拉强度的增加幅度最大,达到14.3%,此时其抗拉强度及伸长率分别为338.57 MPa及15%;SiC颗粒在大的剪切力作用下被破碎细化,在基体中的分布也更加均匀。

等通道转角挤压对L2工业纯铝力学性能的影响

利用等通道转角挤压(ECAP)技术挤压工业纯铝L2,探讨了挤压次数对其力学性能的影响。结果表明,随挤压次数的增加,L2的抗拉强度和硬度得到显著提高,抗拉强度可提高95%,硬度提高70%。挤压1次后,其伸长率由40%下降至15%,此后伸长率基本保持稳定。

铝粉烧结材料等通道转角挤压组织性能演变

对不同路径和不同道次下铝粉烧结材料的等通道转角挤压工艺进行了试验研究,用光学显微镜、扫描电子显微镜和透射电镜分析了粉末烧结材料在不同工艺条件下的晶粒细化规律和致密行为,并测量了挤压后试样的密度和硬度等性能.结果表明,等通道转角挤压工艺对粉末烧结材料具有很强的致密效果和细化效果,可显著提高其力学性能.在单道次变形中,大剪切塑性变形和高静水压力状态是粉末烧结材料获得良好的致密效果的关键;在多道次变形中,变形量的累积和不同的剪切特征不断地改变内部的孔隙形状,使内部基体材料进一步致密.而晶粒的细化效果则取决于变形中的静水压力、变形量和剪切特征等关键因素.

等径道角挤压在AZ91D镁合金半固态加工中的应用

将等径道角挤压工艺(ECAE)应用为应变诱导-熔化激活(SIMA)中的应变诱导工序,并且利用半固态等温处理对ECAE挤压的材料实现熔化激活,提出新SIMA制备AZ91D镁合金半固态坯方法。研究结果表明,新SIMA法制备的AZ91D半固态坯的微观组织均匀、晶粒球化程度好、晶粒细小,平均晶粒尺寸在20μm左右。新SIMA法所制备的半固态坯料半固态触变模锻成形的托弹板的力学性能高,其抗拉强度达到293.5MPa,延伸率达到14.28%。

改进型ECAP路径对Al-Mg_2Si原位复合材料组织与力学性能的影响

采用一种结合BC、BA路径特点的改进型路径BC-UD2、在250℃对铸造Al-10.9%Mg2Si原位复合材料进行等通道转角挤压(ECAP)来细化组织、改善Mg2Si增强相形态及分布状态,考察其对力学性能的影响。结果表明:经BC-UD2路径8道次ECAP挤压后,复合材料基体由约100μm发达的树枝晶组织细化为约1.5μm的细晶粒组织;原先粗大的汉字状共晶Mg2Si相被细化为约0.85μm的多边形状颗粒,趋于均匀分布状态,较常规BC路径中Mg2Si颗粒沿基体晶界聚集分布状态有很大改善;经BC-UD2路径挤压后复合材料的抗拉强度由铸态的166.9 MPa增大到331.8 MPa,伸长率由铸态的0.43%增加到23.6%,分别提高了99%和5 400%;同时也比BC路径挤压材料的抗拉强度(297.3 MPa)提高了12%,伸长率(15.15%)提高了56%,综合力学性能显著提高。

挤压速度对等通道转角挤压6061铝合金力学性能的影响

用自行设计的内角90°,外角30°的等通道转角挤压模具对6061铝合金进行了室温挤压,分析了不同挤压速度对其力学性能的影响。利用金相显微镜和扫描电镜（SEM）观察了金相组织和拉伸断口的形貌特征。结果表明：6061铝合金的断裂特征是韧性断裂,在3道次ECAP变形过程中,随着变形道次增加,6061铝合金的显微硬度和抗拉强度增大。当挤压速度达到35 mm/min时,合金的强度和硬度是最好的。

等通道转角挤压工艺参数对铝镁合金组织和性能的影响

等通道转角挤压技术(ECAP)是一种新型获得超细晶粒的重要制备方法之一,同时也是提高材料力学性能的根本途径之一。影响ECAP对铝、镁合金晶粒细化的因素有多方面,综述了ECAP各工艺参数对铝镁合金组织和性能的影响,其主要工艺参数包括模具结构、挤压道次、挤压温度、挤压速度以及挤压路径。

等通道转角挤压加工对聚丙烯性能的影响

研究了模压成型聚丙烯(PP)经等通道转角挤压(ECAE)加工后的性能。研究表明,一次和二次ECAE加工对PP结晶度和密度的影响较小。PP经一次和二次ECAE加工后其缺口冲击强度均有所提高,且经二次A路径的ECAE加工后试样的缺口冲击强度显著提高,约为PP的18倍;经C路径的二次ECAE加工后试样为各向同性材料,其缺口冲击强度较PP有所提高,拉伸强度下降,断裂伸长率提高,表现出很好的延伸性。

等径道角挤压对Mg-6Al合金性能的影响

为了优化铸态Mg-6Al合金等径道角挤压的工艺参数,通过等径道角挤压实验研究了工艺参数对其性能的影响.研究表明:等径道角挤压可大幅度提高Mg-6Al合金坯料的力学性能.当Mg-6Al合金挤压1道次至4道次后,其力学性能提高较大,微观组织明显细化.随挤压温度从260℃升高至300℃,被挤压坯料的力学性能先提高后降低.当挤压路径为路径B,挤压道次为4道次,挤压温度为300℃时,Mg-6Al合金的力学性能最高,其抗拉强度为308.2 MPa,延伸率达到30.6%.

6061铝合金等通道转角挤压时的流变性能

分别对退火态和固溶时效态6061铝合金进行8道次及4道次等通道转角挤压,用有限元软件Deform-3D模拟变形过程,研究连续大变形对组织性能的影响规律。结果表明:等通道挤压使晶粒破碎细化,金属流线走向与剖面对角线方向基本一致;退火态合金的表面硬度随变形道次增加而升高,各道次挤压载荷峰值没有随着变形道次增加而单调增加,而是经历一个升高、降低、再升高的过程。固溶时效态合金的表面硬度在2道次变形后达到了峰值,其载荷峰值也在第2道次变形时最高。硬度值的变化规律与强化因素及位错的运动有关,而载荷的变化规律与摩擦力的变化及其对载荷的贡献大小有关。模拟结果发现,挤压载荷峰值随着变形道次的增加而增大,与实测值不相符。由于剧烈变形使合金组织性能变化较大,因此需要适当修正材料本构关系,才能正确反映其流变行为。

挤压温度及路径对Mg-Gd-Y-Zn-Zr合金等通道角挤压组织及性能影响

以Mg-13Gd-4Y-2Zn-0. 6Zr镁合金为研究对象进行等通道转角挤压实验,研究了挤压温度以及挤压路径对Mg-Gd-YZn-Zr镁合金的微观组织和力学性能的影响。结果表明,350℃挤压温度下晶粒未发生明显的细化; 400和450℃挤压温度时形变晶粒晶界处发生动态再结晶,晶粒发生细化; 500℃挤压温度时晶界已部分熔化,导致晶界弱化。450℃挤压温度下,铸态和均匀态试样经过1p-ECAP挤压后,在粗大形变晶粒晶界先发生动态再结晶,粗大晶粒和动态再结晶晶粒共存形成双峰组织。均匀态试样1p-ECAP挤压后屈服强度和抗拉强度均提高,屈服强度由145. 0 MPa提高到175. 6 MPa,抗拉强度由254. 3 MPa提高到294. 7 MPa。由于存在双峰组织,细小的动态再结晶晶粒和粗大形变晶粒之间在拉伸过程中变形不协调,容易引起应力集中,导致断裂伸长率降低。A路径4p-ECAP挤压后晶粒细化不均匀,挤压试样不同部位的材料性能存在一定差异; BC路径挤压时由于在下一道次挤压时都转动角度,滑移面出现交叉,晶粒细化比较均匀,挤压试样的屈服强度、抗拉强度和伸长率较高。

等通道转角挤压道次和温度对Cu-Al-Be-B合金组织及力学性能的影响

对Cu-A1-Be-B形状记忆合金进行了等通道转角挤压（ECAP）实验，分析了挤压温度和挤压道次对其组织结构的影响。进行了硬度测试和拉伸试验，研究了挤压道次对合金力学性能的影响。结果表明，在500℃进行ECAP8道次挤压，可将合金硬度从92HI也提高到113HRB，晶粒直径由100-300μm细化至约5μm。但其塑性变差，断裂强度也由465MPa降至340MPa。

具有应变硬化行为的弹塑性材料多道次等通道转角挤压有限元模拟

用有限元模拟方法研究了具有应变硬化行为的弹塑性材料的多道次(至多4道次)等通道转角挤压变形行为。结果表明,随着挤压道次增加,塑性变形区尺寸和对称性增加,拐角缝隙越来越小;按A路径挤压时,应变均匀性越来越差,最大塑性应变区随挤压道次增加向试样前上端移动;按C路径挤压时,应变均匀性越来越好,最大塑性应变区位于试样中心部位;挤压道次相同时,C路径累积最大塑性应变值比A路径要小。