Microstructure and mechanical properties of Mg-Gd-Y-Zr alloy processed by equal channel angular pressing

Microstructure evolution and texture development and their effects on mechanical properties of a Mg-Gd-Y-Zr alloy during equal channel angular pressing（ECAP） were investigated.It is found that the microstructure is still inhomogeneous after four passes,and two zones,namely the fine grain zone（FGZ） and the coarse grain zone（CGZ） are formed.The grain refinement occurs mainly by particle-stimulated nucleation（PSN） mechanism,which led to a more random texture after four passes of ECAP.In the ECAP-processed alloy,the strength did not increase while the ductility was enhanced dramatically compared with the as-received condition.The change of ductility of this alloy was discussed in terms of texture and second phase particles.

AZ31镁合金和7050铝合金ECAP过程的数值模拟研究

利用Abaqus有限元软件分别对AZ31镁合金和7050铝合金进行等通道转角挤压(ECAP)数值模拟研究。利用有限元(FE)模拟得到应力场、应变场及载荷-位移曲线,分析了在不同挤压温度、挤压速度、摩擦条件和不同截面下等通道转角挤压的变形规律。结果表明,挤压温度升高可以降低挤压载荷,这有利于AZ31镁合金挤压,在摩擦较小情况下进行变形有利于降低挤压载荷,提高变形均匀性;在不考虑变形过程中温升效应的情况下,挤压速度对挤压载荷影响较小,当挤压速度提高时,最大等效应变值有所提高;圆形截面比方形截面更适合进行等通道转角挤压。

Microstructure, hardness evolution and thermal stability of binary Al-7Mg alloy processed by ECAP with intermediate annealing

A binary Al-7Mg alloy was processed by equal channel angular pressing （ECAP） at room temperature via route Bc, combined with intermediate annealing. After 6 passes, a high hardness of HV218 is achieved. Transmission electron microscopy （TEM） observations demonstrate that ECAP leads to a significant grain refinement and ultrafine grains down to 100-200 nm are developed after 5 or 6 passes. X-ray diffraction （XRD） analysis indicates that the major part of Mg atoms are in solid solution in the deformed material, and the possible strengthening effect of Mg solute atom clusters or precipitates is neglected. The high hardness of the 6 pass-treated materials comes mainly from grain boundary strengthening, which contributes about 41% to the total strength, while dislocations and Mg solid solution contribute about 24% and 35% to the remaining strength, respectively. Also, the thermal stability of this severely deformed material was investigated by hardness measurements. The material is relatively stable when annealed at a temperature lower than 250 ℃, while annealing at 300 ℃ leads to a rapid softening of the material.

The effect of Equal Channel Angular Pressing process on the microstructure of AZ31 Mg alloy strip shaped specimens

Equal Channel Angular Pressing(ECAP)is one of the most applicable Sever Plastic Deformation(SPD)processes which leads to strength and ductility improvement through the grain refining and development of a suitable texture.In this study,after designing and manufacturing a suitable die,4 pass ECAP process at route C is done on strip shaped specimens of AZ31 magnesium alloy in order to achieve desirable microstructural and mechanical properties.Microstructure then got studied through the optical microscopy.Results show that mean grain size is decreased and grain size distribution got close to normal distribution state by increasing the pass number.However,the grain size is reduced by increasing of ECAP temperature.

Effect of processing routes on microstructure and mechanical properties of 2014 Al alloy processed by equal channel angular pressing

Al-Cu alloy was deformed through equal channel angular pressing(ECAP) by routes A,Ba,Bc and C up to 5 passes.ECAP was done using a 90° die for three different conditions,namely 1) as received,2) solutionised at 768 K for 1 h and 3) solutionised at 768 K for 1 h + aged at 468 K for 5 h.The microstructure,microhardness and tensile strength were studied for all the three conditions and four routes.Significant improvement in hardness(HV 184 after five passes) and strength(602 MPa after three passes) was observed in solutionised and aged 2014 Al alloy deformed through route Bc.Microstructure evolution was reasonably equiaxed in route Bc with aspect ratio of 1.6.Solutionised and aged 2014 Al alloy deformed through route Bc was identified to have better microstructure and mechanical property than the other processing routes and conditions.

Microstructure evolution and mechanical behavior of AZ31 Mg alloy processed by equal-channel angular pressing

AZ31 Mg alloy bar was subjected to 8-pass equal-channel angular pressing(ECAP) at 623 K. Microstructure evolution was observed by optical microscopy(OM) on cross section and X-ray diffraction analysis. The room temperature mechanical properties of the ECAP processed specimens were also investigated. A fine-grained structure with an average sub-grain size of 9 μm is obtained after 7 ECAP passes. XRD analysis indicates that after ECAP,in placing of {1 010},planes {1 011} and {1 012} become the dominant directions that are favourable for grain refinement. ECAP processed AZ31 Mg alloy exhibits significant improvement in elongation but decrease in strength. The elongation of the specimen increases continuously up to 2 passes and then remains stable at further passes. This improvement can be related to the evolution of crystallographic texture and the scattered orientation of the basal plane(0001).

Microstructure and Properties of Mg-12Gd-3Y-0.5Zr Alloys Processed by ECAP and Extrusion

Equal channel angular pressing （ECAP） processing and conventional extrusion （Ex） were applied to the Mg-12Gd-3Y-0.5Zr （wt%） magnesium alloy in order to evaluate the potential improvement in the mechanical properties. The ECAP experiment was conducted at 380 ℃ in a die having an included angle of 90° between two channels by the Bc route with the billet rotated by 90° about its longitudinal axis. Subsequently, some billets were processed by conventional extrusion at 300 ℃. The microstructures were examined by X-ray diffraction （XRD）, optical microscopy and transmission electron microscopy （TEM）. The experimental results indicate that the grain size is refined effectively, but the basal planes are highly inclined （about 40o） from the extrusion axis introduced by ECAP, which impairs the grain boundary strengthening effect. The conventional extrusion, following the ECAP, can modify the grains in hard orientation. Based on grain boundary strengthening due to ECAP and texture strengthening due to Ex, the strength is improved effectively. The enhanced activity of the non-basal slips, due to the refined grains and the reduction in c/a ratio, is responsible for good ductility and high strain hardening rate in samples obtained by the two-step process.

DSC analysis of commercial Cu-Cr-Zr alloy processed by equal channel angular pressing

Samples of a commercial Cu-lCr-0.1Zr(mass fraction,%) alloy were subjected to equal channel angular pressing(ECAP) up to 16 passes at room temperature following route Bc.Differential scanning calorimetry(DSC) was used to highlight the precipitation sequence and to calculate the stored energy,recrystallization temperature and activation energy after each ECAP pass.On another hand,electrical properties were correlated with the dislocation density.Results show that the stored energy increases upon increasing ECAP pass numbers,while the recrystallization temperature decreases significantly.

Effect of hot isostatic pressing processing parameters on microstructure and properties of Ti60 high temperature titanium alloy

Hot isostatic pressing parameters are critical to Ti60 high temperature titanium alloy castings which have wide application perspective in aerospace.In order to obtain optimal processing parameters,the effects of hot isostatic pressing parameters on defects,composition uniformity,microstructure and mechanical properties of Ti60 cast high temperature titanium alloy were investigated in detail.Results show that increasing temperature and pressure of hot isostatic pressing can reduce defects,especially,the internal defects are substantially eliminated when the temperature exceeds 920℃or the pressure exceeds 125 MPa.The higher temperature and pressure can improve the microstructure uniformity.Besides,the higher pressure can promote the composition uniformity.With the temperature increases from 880℃to 960℃,α-laths are coarsened.But with increasing pressure,the grain size of prior-βphase,the widths ofα-laths andα-colony are reduced.The tensile strength of Ti60 alloy is 949 MPa,yield strength is 827 MPa,and the elongation is 11%when the hot isostatic pressing parameters are 960℃/125 MPa/2 h,which exhibits the best match between the strength and plasticity.

Deformation mechanism at impact test of Al-11% Si alloy processed by equal-channel angular pressing with rotary die

Al-11%Si(mass fraction)alloy was transformed into a ductile material by equal-channel angular pressing(ECAP)with a rotary die.Two mechanisms at impact test,slip deformation by dislocation motion and grain boundary sliding,were discussed.The ultrafine grains with modified grain boundaries and the high content of fine particles(<1μm)were necessary for attaining high absorbed energy.The results contradict the condition of slip deformation by dislocation motion and coincide with that of grain boundary sliding.Many fine zigzag lines like a mosaic were observed on the side surface of the tested specimens.These observed lines may show grain boundaries appeared by the sliding of grains.

Microstructural evolution of a recycled aluminum alloy deformed by equal channel angular pressing process

The microstructural evolution of a recycled aluminum alloy after equal channel angular pressing （ECAP） up to four passes was investigated using X-ray diffxaction （XRD） analysis and transmission electron microscopy （TEM）. Microhardness tests were performed to determine the associated changes in mechanical properties. An ultrafine-grained material has been obtained with a microstructure showing a mixture of highly strained crystallites. A high density of dislocations was achieved as a result of severe plastic deformation （SPD） through the die. Changes in mechanical behavior are also revealed after ECAP due to strain hardening. Thermal analysis and TEM micrographs ob- tained after annealing indicate the succession of the recovery, recrystallization, and grain growth phenomena. Moreover, the energy stored during ECAP may be related to the dislocation density introduced by SPD. We finally emphasize the role played by the precipitates in this alloy.

LPSO相调控对ECAP挤压Mg-Y-Zn-Al合金组织和力学性能的影响

针对含18R-LPSO相铸态Mg-Y-Zn系合金塑韧性差、变形后力学性能提高有限的问题,研究了固溶、铸态+ECAP挤压和固溶+ECAP对Mg-3.74Y-1Zn-0.5Al(at%)合金力学性能的影响。结果表明,固溶处理诱发18R→14H-LPSO相转变、Al(Y,Zn)相化合物颗粒破碎细化,改善了合金的塑性,但强度几乎不变。铸态+ECAP挤压导致18R-LPSO和Al(Y,Zn)相破碎,并诱发大量α-Mg晶粒发生再结晶。固溶+ECAP挤压使14H-LPSO相弯曲或扭折变形、细小Al(Y,Zn)颗粒均匀分散,仅少数α-Mg晶粒发生再结晶,其强度、塑韧性远高于铸态+ECAP挤压合金的。良好强度、塑韧性匹配的14H-LPSO相的大量形成、α-Mg基体再结晶被抑制及细小Al(Y,Zn)颗粒的均匀分散是其性能提高的主要原因。

Equal-Channel Angular Pressing as a New Processing to Control the Microstructure and Texture of Metallic Sheets

The extended band structures of as-cold-rolled high Cr steel sheets are recrystallisation-resistant, and tend to become aggregates of the so-called grain colonies as a partially recovered state after final annealing. Such band structures diminish formability and become origin of the so-called ridging. A novel processing will be shown here, which involves strain-path change by introducing one-pass ECAP prior to cold-rolling, and facilitates recrystallisation. Indeed, the recrystallisation temperature was reduced by 100℃, compared with cold-rolling alone imposing an equivalent strain. Grain- scale microshear bands introduced during one-pass ECAP perturbed the banded structures in post-ECAP cold-rolling and enhanced the recrystallisation at the final annealing.

Microstructural Development of Fe-20mass%Cr Alloys and Pure Copper Processed by Equal-Channel Angular Pressing

Microstructural development of ultra low C, N, Fe-Cr alloy and pure copper processed by equal-channel angular pressing (ECAP) have been examined focusing on the initial stage of the formation of ultrafine grain structure. Fe-Cr alloys were pressed at 423 K while pure copper at room temperature for 1 to 3 passes via the route Bc to compare at the equivalent homologous temperature. Microstructural evolutions were characterized by electron backscatter diffraction (EBSD) image and transmission electron microscopy (TEM). It was found that deformation structures were mostly deformation-induced subboundaries in both the materials after one pass, but the fraction of high-angle grain boundary became higher in the Fe-Cr alloys than in pure copper in subsequent passes by increasing misorientation of the boundaries. The more enhanced formation of high angle boundaries in Fe-Cr alloys was discussed in terms of the nature of crystal slip of FCC and BCC structures.

ECAP对预置孪晶AZ31镁合金组织和力学性能的影响

为了探究剪切变形对预置孪晶AZ31镁合金组织和力学性能的影响,对应变量为5%的预置孪晶试样在250℃进行了不同道次的等通道转角挤压(ECAP),随后对不同状态试样进行了显微组织观察和室温单轴拉伸测试。结果表明:预置孪晶试样经过ECAP变形后,试样组织与商用挤压态合金相比明显细化,延展性获得较大提高;且随着挤压道次的增加,合金晶粒更加细小均匀,延展性改善更加显著。其中,挤压四道次合金的室温断后伸长率较挤压态棒材提高了约163%,表明预置孪晶后引入剪切变形能有效提高镁合金棒材的室温塑性。

ECAP和时效对Mg-4Zn-1Mn-0.5Ca合金组织和性能的影响

将铸态Mg-4Zn-1Mn-0.5Ca合金在300℃热挤压成棒材,对棒材进行180℃时效处理和200℃等通道转角挤压(ECAP)。研究了热挤压合金、ECAP 8道次合金和时效后ECAP 8道次合金的组织和性能。随后对试样进行室温和150℃低温单轴拉伸。结果表明:8道次ECAP后合金比热挤压态合金具有更细、更均匀的晶粒组织,同时提高了合金的室温屈服强度。时效后ECAP 8道次合金的150℃断裂伸长率比未时效ECAP8道次合金提高17.4%,说明时效处理对合金性能起着重要作用。

Optimization of the Hot Pressing Process for Preparing Flax Fiber/PE Thermoplastic Composite

The hot pressing process parameters were optimized to prepare flax fiber reinforced polyethylene(PE)thermoplastic composite by the Taguchi method.The optimal hot pressing process parameters were determined to increase the tensile strength of the composite.The optimal parameters of the design include the following sections:hot pressing temperature,pressure,hot pressing time and coupling agent modification time.An L9(3*4)orthogonal matrix based on the Taguchi method was created.By means of analysis of signal-to-noise ratio and analysis of variance,the optimal hot pressing process parameters combination was found,compared to the average tensile strength in the nine design experiments,and the tensile strength was improved nearly 10%.

Effects of second phases on mechanical properties and martensitic transformations of ECAPed TiNi and Ti-Mo based shape memory alloys

TiNi and Ti-based shape memory alloys were processed by equal channel angular pressing （ECAP） at 673-773 K along Bc route to obtain ultrafine grains for increasing the strength of parent phase and improving the functional properties. The effects of both thermodynamically stable and metastable second phases on the mechanical properties and martensitic transformations of these alloys were investigated. It is found that thermodynamically stable Ti2Ni phase has no effect on martensitic transformation and superelasticity of Ti-rich TiNi alloy, thermodynamically stable α phase is harmful for ductility of Ti-Mo-Nb-V-Al alloy, but metastable Ti3Ni4 phase is effective for R phase transformation, martensitic transformation and superelasticity of Ni-rich TiNi alloy. The mechanisms of the second phases on the martensitic transformations and mechanical properties were discussed.

等通道转角挤压(ECAP)工艺的研究现状

等通道转角挤压(ECAP)是一种大塑形加工技术,可细化合金组织,改善性能,提高材料的成形性。本文概述ECAP法的基本原理、剪切模式与变形规律,分析摩擦因素对变形的影响,综述中国在ECAP合金组织、性能方面的一些研究成果。

ECAP法制备细晶ZK60镁合金的微观组织与力学性能

利用等通道转角挤压法（ECAP）制备出了细晶ZK60合金,通过金相组织观察,拉伸性能测试,EBSD和透射电镜（TEM）研究了不同挤压温度和挤压道次对合金组织与性能的影响。结果表明：ZK60镁合金在210~240℃温度范围内进行ECAP挤压能获得较好的晶粒细化效果;在240℃进行ECAP挤压时,随着挤压道次的增加,合金晶粒得到明显的细化,经过4道次挤压后,合金晶粒可细化到2.8μm;但是超过4道次后,合金的细化效果减慢;合金ECAP后的屈服强度与变形前相比降低,合金的伸长率经过多道次变形后得到明显提高。