等通道转角挤压制备超细晶Mg15Al双相合金组织与性能

对高铝双相合金Mg15Al在553K以Bc路线进行了不同道次的等通道挤压(ECAP),获得了超细晶高铝镁合金。通过OM,SEM,TEM分析了ECAP前后合金的微观组织结构及断口形貌,并测试了不同挤压道次后合金的硬度和室温拉伸性能,分析了ECAP细化晶粒机理及其性能改善原因。结果表明,随挤压道次增加,累计形变增强,网状硬脆相β-Mg17Al12破碎,合金晶粒显著细化,但对单相区和两相混合区细化效果不同。在α、β两相共存区内,4道次ECAP后形成100nm～200nm的细晶粒;在α单相区,4道次ECAP后晶粒为1μm以下,且在初晶α-Mg内析出弥散细小的β相,起到细晶强化和弥散强化作用。8道次ECAP后,晶粒略有长大。ECAP使合金的硬度、抗拉强度和延伸率同时得到提高,尤其是4道次ECAP后,硬度提高了32.04%,抗拉强度σb从150MPa提高到269.3MPa,延伸率δ由0.05%提高到7.4%;8道次ECAP后,硬度、抗拉强度略有下降,延伸率略有上升。SEM断口观察显示ECAP使合金拉伸断口形貌由铸态的解理断裂特征转变为延性韧窝断裂特征。     

MB15合金等通道转角挤压组织模拟和实验分析

采用等通道转角挤压(ECAP)对MB15合金试样进行挤压,利用有限元软件DEFORM-3D进行ECAP晶粒组织模拟,探索采用有限元模拟与实验分析相结合的方法,研究镁合金ECAP成形过程的晶粒组织变化规律。模拟结果表明:数值模拟后试样从头部P1处、中部P2处到尾部P3处的晶粒组织细化程度明显减小,平均晶粒尺寸从初始的13.32μm减小到2.3~3.1μm;采用ECAP方法进行一道次挤压,试样的平均晶粒尺寸从13.32μm减小到2.2μm。对比数值模拟与实验分析结果表明:两者在晶粒细化程度上吻合良好。     

Effects of die angle on microstructures and mechanical properties of AZ31 magnesium alloy processed by equal channel angular pressing

1　INTRODUCTIONMagnesiumalloysarethelightestmetallicstruc turalmaterialsandhencetheyprovidegreatpotentialintheweightsavingofautomotiveandaerospacecomponents ,materialhandlingequipment ,portabletoolsandevensportinggoods[1,2 ] .Duetotheirhexago nalclose packed (HCP)crystalstructure ,magnesiumalloysperform poorformabilityandlimitedductilityatroomtemperature ,thustheirproductsaremainlyfabricatedbycasting ,inparticular ,die casting ,andtheapplicationsofwroughtmagnesiumalloysarelim ited .Nowit…     

Superplasticity of fine-grained AZ31 Mg alloy sheets

Superplastic mechanical properties of fine-grained AZ31 Mg alloy sheets in the temperature range of 250 - 450 ℃ and strain rate range of 0.7 × 10-3- 1.4 × 10-1 s-1 were investigated by uniaxial tensile tests. The microstructure evolution during the superplastic deformation of AZ31 Mg alloy was examined by means of metallurgical microscope and transmission electronic microscope (TEM). It is shown that, fine-grained AZ31 Mg alloy starts to exhibit superplasticity at 300 ℃ and the maximum elongation of 362.5% is obtained at 400 ℃ and 0.7× 10-3 s-1.The predominate superplastic mechanism of AZ31 Mg alloy in the temperature range of 300 -400 ℃ is grain boundary sliding (GBS). Twinning caused by pile-up of dislocations during the early stage of superplastic deformation is the hardening mechanism, and dynamic continuous recrystallization (DCRX) is the important softening mechanism and grain stability mechanism during the superplastic deformation of the alloy.     

Observation of macroscopic shear band in aluminum-based alloy during equal-channel angular pressing

1　INTRODUCTIONInrecentyears ,bulkultrafine grained (UFG )materialsprocessedbymethodsofsevereplasticdefor mation (SPD)suchassevereplastictorsionstraining(SPTS)andequalchannelangularpressing (ECAP)haveattractedthe growinginterestofspecialistsinmaterialsscience[1] .Thisinterestisconditionedbyu niquephysicalandmechanicalproperties .Itisageneralobservationinmanyoftheindus trialformingprocessesthatplasticinstabilitydevelopsathighstrainlevels (generally >1.0oftruestrain) ,andshearbands ,or…     

Microstructure and tensile properties of ultrafine grained copper processed by equal-channel angular pressing

1. Introduction There has been an interest in the research of spe- cific microstructure and unique mechanical proper- ties in ultrafine-grained (UFG) materials [1]. Equal-channel angular pressing (ECAP) process has been successfully applied to obtain UFG structure in numerous metals and alloys [2-6]. However, there are some deficiencies on copper deformed to large shear strains. Ferrasse et al. [6] argued that intense simple shear promotes dynamic rotation recrystalli- zation during ECAP…     

Tensile properties of 2024 Al alloy processed by enhanced solid-solution and equal-channel angular pressing

Equal-channel angular pressing（ECAP） of an enhanced solid-solution treated 2024 Al alloy was successfully performed at room temperature, with an imposed equivalent normal strain of about 0.5. A very high hardness about HV191 and yield strength about 610 MPa （30% higher than those of the unECAPed 2024 Al alloy） in terms of commercial aluminum alloys were observed for the ECAPed 2024 Al alloy. In addition to the strengthening, this process allows the ECAPed 2024 Al alloy have a moderate level of tensile ductility （about 12.7%） and a significant strain hardening capability up to tensile failure. After aged at 373 K for 48 h, the ECAPed alloy increases its hardness （about HV201） and tensile ductility （about 14 %） further. The TEM results show that the ECAPed 2024 AI alloy presents a plate structure （about 50-100 nm） with high density of dislocation and additional thin plate （approximately 〈10 nm= inside. The XRD results show that the ECAP processing decreases the texture and increases the dislocation density of the alloy considerably. The theoretical calculations show that the increase of dislocation density resulting from ECAP processing makes a considerable contribution about 55.2 % for the improvement of yield strength.     

等径角挤压处理后的Mg-Gd-Y-Zr合金的微观组织和力学性能

研究等径角挤压过程中材料的微观组织和织构演变以及对其力学性能的影响。结果表明：挤压4道次后的微观组织是不均匀的,即在此过程中形成了粗晶区和细晶区2个区域。颗粒诱发的再结晶机制导致晶粒细化,在4道次后形成了更加随机的织构。与挤压前的原始材料相比较,经等径角挤压处理的材料虽然强度没有增加,但是塑性有了显著的提高。用织构改变和第二相颗粒解释了合金塑性的变化。     

Factors influencing microstructural development in equal-channel angular pressing

Processing through the imposition of severe plastic deformation (SPD) provides an opportunity for achieving very significant grain refinement in bulk materials. Although different SPD procedures are available, the process of equal-channel angular pressing (ECAP) is especially attractive because it can be scaled easily to produce relatively large samples. This paper describes the principles of ECAP processing and demonstrates the potential for achieving unusual mechanical properties in the samples subjected to ECAP. Special emphasis is placed on the possibility of attaining a high strain rate superplastic forming capability in the as-pressed materials: examples are presented for an Al−Mg−Sc alloy prepared in the laboratory by casting and for a commercial Al-2024 alloy. This article is based on a presentation made in the 2002 Korea-US symposium on the “Phase Transformations of Nano-Materials,” organized as a special program of the 2002 Annual Meeting of the Korean Institute of Metals and Materials, held at Yonsei University, Seoul, Korea on October 25–26, 2002.     

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.     

Effects of microstructure evolution on discharge properties of AZ31 alloy as anode for seawater battery

In recent years, many researchers have been focusing on improving the discharge properties of AZ31 magnesium alloy for battery applications. In this paper, the equal-channel angular pressing (ECAP) is used as a preferred way of refining the microstructure to enhance the discharge characteristics of AZ31 alloy as the anode for seawater batteries. The electrochemical discharge behaviors of ECAP-processed AZ31 alloy are investigated along extrusion surfaces, normal cross-sections, and transverse cross-sections and compared with as-cast and homogenized samples. On the basis of the findings, the anode efficiency is improved effectively through the ECAP method, with approximate isotropy in the discharge behaviors of refined AZ31 alloy. The enhanced discharge performance can be attributed to the refined grains, uniform grain sizes, and dispersed β-Mg₁₇Al₁₂ after ECAP processing.     

等径弯曲通道变形制备高性能Cu-Cr合金的组织性能

用两种方式等径弯曲通道变形(equal-channel angular pressing,简称ECAP)制备了的具有等轴晶组织的超细晶Cu-0.4Cr合金,晶粒尺寸为500nm。研究了不同挤压方式、不同挤压道次合金的组织和性能的变化。探讨了不同退火温度对5～8道次材料导电率和硬度的影响。结果表明,经ECAP挤压后的Cu-0.4Cr合金具有很好的综合性能,拉伸强度可达565MPa;硬度和导电率分别为225 HV和66.4%IACS;723K退火1h后材料的导电率和硬度可达80.3%IACS和210.9HV;软化温度可达723K。     

Microstructure and mechanical properties ofAZ31 Mg alloy processed by high ratio extrusion

The microstructure and mechanical properties of AZ31 Mg alloy processed by high ratio extrusion （HRE） were investigated. General extrusion with extrusion ratio of 7 and high ratio extrusion with extrusion ratio 100 were contrastively conducted at 250, 300 and 350 ℃. The results show that HRE process may be applied successfully to AZ31 Mg alloy at temperatures of 250, 300 and 350 ℃ and this leads to obvious grain refinement during HRE process. The strength of HRE process is improved obviously compared with that of general extrusion. The grain refining mechanism of HRE process was also discussed. The current results imply that the simple high ratio extrusion method might be a feasible and effective processing means for refining the microstructure and improving the mechanical properties ofAZ31 Mg alloy.     

等通道转角挤压Mg-3.52Sn-3.32Al合金的组织与力学性能

采用等通道转角挤压（ECAP）Bc路径对固溶态Mg-3.52Sn-3.32Al合金分别挤压1、4和8道次。利用光学显微镜、扫描电子显微镜、透射电子显微镜和X射线衍射仪分析合金的组织和相组成,并测试了其室温拉伸力学性能。结果表明,经ECAP挤压后,固溶态合金组织中析出大量细小的Mg2Sn相和极少量的Mg17Al12相。随挤压道次增加,合金的综合力学性能先提高后降低。经4道次挤压后,合金的综合拉伸力学性能相对较佳,抗拉强度、伸长率和硬度分别达到250 MPa、20.5%和61.3 HV9.8,较未ECAP时分别提高43.7%、105%和26.9%。经ECAP挤压的合金室温拉伸断口均呈韧性断裂。等通道转角挤压Mg-3.52Sn-3.32Al合金的力学性能受晶粒尺寸、析出相以及组织织构的共同影响。     

Effect of equal-channel angular pressing on pitting corrosion resistance of anodized aluminum-copper alloy

The effect of equal-channel angular pressing(ECAP) on the pitting corrosion resistance of anodized Al-Cu alloy was investigated by electrochemical techniques in a solution containing 0.2 mol/L AlCl₃ and also by surface analysis. Anodizing was conducted for 20 min at 200 and 400 A/m² in a solution containing 1.53 mol/L H₂SO₄ and 0.018 5 mol/L Al₂(SO₄)₃·16H₂O at 20 °C. Anodized Al-Cu alloy was immediately dipped in boiling water for 20 min to seal the micro pores present in anodic oxide films. The time required before initiating pitting corrosion of anodized Al-Cu alloy is longer with ECAP than without, indicating that ECAP process improves the pitting corrosion resistance of anodized Al-Cu alloy. Second phase precipitates such as Si, Al-Cu-Mg and Al-Cu-Si-Fe-Mn intermetallic compounds are present in Al-Cu alloy and the size of these precipitates is greatly decreased by application of ECAP. Al-Cu-Mg intermetallic compounds are dissolved during anodization, whereas the precipitates composed of Si and Al-Cu-Si-Fe-Mn remain in anodic oxide films due to their more noble corrosion potential than Al. FE-SEM and EPMA observation reveal that the pitting corrosion of anodized Al-Cu alloy occurs preferentially around Al-Cu-Si-Fe-Mn intermetallic compounds, since the anodic oxide films are absent at the boundary between the normal oxide films and these impurity precipitates. The improvement of pitting corrosion resistance of anodized Al-Cu alloy processed by ECAP appears to be attributed to a decrease in the size of precipitates, which act as origins of pitting corrosion.     

侧向等径挤压过程中的材料组织演化规律

论述了采用侧向等径挤压简称(ECAE／ECAP)技术制备超细晶材料的基本原理和组织演化过程。试验采用紫铜棒作为试样，在室温下进行了多道次挤压，等径挤压后，原始晶粒中产生了大量位错缠结和位错胞，随着挤压道数的增加，由原来被拉长的显微组织逐渐变成等轴显微组织。挤压4道次后，变形织构消失，挤压6道次后，位错胞崩塌变成为亚晶或晶粒，之后，晶界会不断增厚以及晶粒旋转，使亚晶变成大角度均匀的等轴超细晶，其晶粒尺寸为500nm～1μn。     

等径角轧制AZ31镁合金板材的组织与性能

采用等径角轧制工艺制备了AZ31镁合金板材.结果表明:经等径角轧制后的板材,晶粒取向由等径角轧制前的(0002)基面取向演化为基面与非基面共存的取向.与等径角轧制前的板材相比,板材晶粒尺寸略有长大并有孪晶出现,但强度却明显提高,而断裂延伸率变化不大,尤其是1个道次轧制的板材其抗拉强度由等径角轧制前的240增大到275 MPa,屈服强度由193.8增大到239.2 MPa;随着等径角轧制道次的增加,板材的强度逐渐降低,至第4个道次其抗拉强度仅为250 MPa,屈服强度为207.3 MPa.     

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.     

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.