EBSP study of the annealing behavior of aluminum deformed by equal channel angular processing

Commercial purity aluminum (99.5%) was fabricated by equal channel angular pressing (ECAP) up to total accumulated strains of approx. 10. The annealing behavior of material deformed to total strains of approx. 1 and 10 was investigated, using heat treatments of 2 h at various temperatures from 100 to 500 °C. The microstructure of the annealed materials was characterized using the electron back-scatter pattern technique. A number of parameters were determined including the distribution and average values of both the boundary spacings and misorientations. For samples deformed to a total strain of 1, annealing resulted in discontinuous recrystallization. For samples deformed to a total strain of 10, annealing resulted in microstructures exhibiting characteristics of both uniform coarsening and, in a number of places, of discontinuous recrystallization. An attempt was made, based on the boundary spacing distributions, to separate these two components. The grain size after annealing was still however small, being just 6.4 μm after 2 h at 300 °C.     

Analytical modeling of material flow in equal channel angular extrusion (ECAE)

We provide analytical forms for the plastic deformation and velocity gradients associated with a single pass of equal channel angular extrusion (ECAE). Three cases of plastic deformation are considered: ideal simple shear, a plastic deformation zone (PDZ) in the shape of a central fan of angle β_m, and a two-part PDZ consisting of a central fan in the ‘upper’ region and a low intensity shear deformation in the ‘lower’ region. The analysis for simple shear considers a general die angle Φ, whereas the other two cases only consider Φ=90°. The tensors for deformation and velocity gradients completely describe the deformation, such as the directions and magnitudes of material stretching and rotations. From this analysis, one can calculate deformation and texture evolution. Texture evolution during flow through the central fan zone involves continuous rotation of the texture components causing the texture developed at the end of the extrusion to be rotated relative to the ideal simple shear case. The analysis of the two-part zone suggests inhomogeneity in texture evolution, in which features of the initial texture are retained and rotated in the lower region, while they are nearly erased in the upper region. These analytical flow patterns for a single pass can be repeatedly applied for any number of passes of any ECAE route.     

Microstructure and Properties of Al-6061 Alloy by Equal Channel Angular Extrusion for 16 Passes

The experimental researches on Equal Channel Angular Extrusion (ECAE) process of commercial available Al-6061 alloy were conducted and the grain refinement after ECAE processing was investigated. Sixteen passes of ECAE processing at room temperature were conducted and the relationship of grain refinement with extrusion pass was established. The property enhancements after ECAE processing including ultimate tensile strength and Vickers microhardness were investigated to determine the effects of the number of ECAE passes on the mechanical properties of the extruded samples. The research presents a whole picture of ECAE processing of the alloy for up to 16 passes.     

Determining dislocation cell sizes for high-strain deformation microstructures using the EBSP technique

The effect of several data collection and processing choices has been examined for high‐resolution electron back‐scatter pattern (EBSP) investigation of a highly deformed sample. The results were compared with a transmission electron microscope (TEM) investigation of the same sample. The estimated dislocation cell size was examined as a function of data cleaning strategy, line intercept vs. reconstruction method, critical misorientation angle definition and step‐size. The best agreement with the TEM results was obtained using a modified relative reconstruction algorithm on fine step‐size maps allowing some of the noise in the data to be overcome. Step sizes of up to one‐quarter the average cell size yielded similar values for the estimated average cell size. As a result of the mixture of both high‐ and low‐angle boundaries, single diffraction condition TEM images may give larger cell size estimates than the EBSP data. Orientation noise in the EBSP data, however, still limits the extent to which quantitative information can be extracted.     

等径角挤压对AZ31镁合金组织及力学性能的影响

研究了电磁连铸AZ31镁合金沿A路径经常规等径角挤压(ECAE)和两步ECAE变形后的微观组织与力学性能.结果表明:与预挤压态相比,常规ECAE态合金随着挤压道次的增加,晶粒不断细化,伸长率不断提高,但屈服强度与抗拉强度逐渐降低;两步ECAE可以使晶粒进一步细化,伸长率、屈服强度与抗拉强度均提高.伸长率、屈服强度与抗拉...     

Evolution of damage in AA-5083 processed by equal channel angular extrusion using different die geometries

In this study, the influence of the die geometry on the introduced damage of the processed parts by ECAE is studied. It will be shown experimentally and by FEM simulations that the die geometry greatly influences the imparted damage, if the die geometry is not selected adequately. This could lead to obtain processed materials which could be useless for posterior mechanical applications because of cracks nucleated inside of them, which will decrease the mechanical properties such as fatigue resistance and formability among others.Several FEM models have been solved in order to obtain a mathematical model to predict the influence of the die geometry.Moreover, several parts have been processed using different die geometries in order to determine the damage within the processed material experimentally and also to validate FEM simulations. A 5083 aluminium alloy in (O) state, which means that has been fully annealed, has been selected and different die geometries have been manufactured for processing this aluminium alloy.     

Reheating and thixoforging of ZK60+RE alloy deformed by ECAE

The two-pass equal channel angular extrusion (ECAE) process was introduced into strain-induced melt activation (SIMA) to predeform a ZK60 alloy with rare earth (RE) addition. Microstructure evolution of ECAE-formed ZK60+RE alloy during reheating was investigated. Furthermore, tensile properties of thixoforged components were determined. The results show that the SIMA process can produce ideal microstructures, and spheroidized solid particles with little entrapped liquid can be obtained. With prolonging hold...     

铜单晶ECAE过程的剪切特征

以铜单晶为模型材料,采用扫描电镜电子通道衬度术（ＳＥＭ－ＥＣＣ）和透射电子显微技术,在不同民度上研究了单次和两次等通道转角挤压过程珠剪切形变特征结果表明：（１）一次ＥＣＡＴ挤压产生的剪切形变取向与理论预测和相接近,但剪切形变表现出局部化特征,出现了微观尺度上的剪切带;（２）两次ＥＣＡＥ产生的两套剪切带间存在着交互作用,导致剪切带出现分叉现象,方向也与理论预测结果与偏差,但仍能保持其各道 剪切特征     

等通道转角挤压对Mg-1Gd、Mg-2Zn二元合金的组织及力学性能的影响

本文使用金相、EBSD等手段研究了等通道挤压对Mg-1Gd、Mg-2Zn两种二元合金组织和力学性能的影响。结果表明,在相同挤压条件下,Mg-2Zn合金发生完全再结晶,晶粒长大粗化,且强度塑性不随着挤压道次变化;Mg-1Gd合金则只发生了部分动态再结晶,组织为细小的动态再结晶晶粒和变形晶粒,伴随挤压道次的增加,再结晶程度提升,合金的抗拉强度与塑性增加了一倍。这与溶质原子Gd比Zn更能抑制再结晶和晶粒长大有关。Mg-1Gd合金的再结晶晶粒的取向分散,而未再结晶的晶粒c轴取向由ED向TD偏转45°,这与宏观织构的检测相互印证,晶粒内部产生大量的小角度晶界,小角度晶界两侧发生围绕c轴的转动,并逐渐演化为大角度晶界。     

等通道角挤压AZ91D镁合金热压缩变形行为

在应变速率为0.005~1 s~(-1)、温度200~275℃条件下,利用Instron-5500热模拟机,对经过等通道角挤压(Equal Channel Angular Extrusion,ECAE)后的AZ91D镁合金的高温压缩特性进行了研究,得到了ECAE-ed态AZ91D镁合金真实应力-应变曲线,分析了挤压温度、应变速率等对其的影响,得出本构方程的一系列常量,建立了ECAE-ed态AZ91D镁合金在高温压缩中的本构方程关系式,并与铸态AZ91D镁合金进行了对比。结果表明:热压缩过程中,ECAE-ed态AZ91D镁合金与铸态一样,流动应力随温度的升高而降低,随应变速率的升高而升高;流动应力也可以用双曲正弦函数来描述,且双曲正弦值随Zener-Hollomon参数的自然对数的升高呈线性升高;两者同为正应变速率敏感材料,但ECAE-ed态AZ91D镁合金要比铸态应变速率敏感性小,其指数从铸态的m=0.14下降为0.096,变形激活能从182.65 kJ/mol上升为227.14 kJ/mol。研究结果对AZ91D镁合金进一步塑性成形和应用具有指导意义。