累积叠轧工艺对AZ31镁合金板材组织和性能的影响

采用累积叠轧工艺对AZ31 镁合金薄板进行剧塑性变形,研究了累积叠轧变形过程中镁合金板材的组织及性能演变.实验结果表明,累积叠轧可以有效细化AZ31镁合金板材的晶粒组织,显著改善室温延伸率,是制备大尺寸、高性能细晶镁合金板材的一种有效、经济而且可以实现工业化生产的技术.累积叠轧5道次后AZ31镁合金板材组织均匀,晶粒尺寸为1～2μm左右,晶粒细化源于大的累积变形及表面剪切变形;室温抗拉强度和延伸率可达到349MPa和22.46%,可归因于晶粒细化对镁合金强度和塑性的改善.累积叠轧板材的道次间的加热使ARB组织粗化,减小了累积叠轧过程中晶粒持续细化的效果.     

累积叠轧焊温度对AZ31镁合金板材组织与性能的影响

目的研究叠轧温度对AZ31镁合金板材组织与性能的影响。方法在450℃和550℃下,对AZ31镁合金板材进行2道次叠轧,研究不同温度下板材界面裂纹的金相组织、RD-ND面晶体取向、力学性能以及断面形貌的异同。结果 450℃累积叠轧制备的ARB2镁合金板材室温断裂伸长率为2.3%,550℃累积叠轧制备的ARB2镁合金板材室温断裂伸长率为8%;450℃叠轧板材中动态再结晶晶粒大多数尺寸约为1～3μm左右,550℃叠轧板材中动态再结晶晶粒大多数尺寸约为600 nm～2μm。结论通过提高温度,可改善界面结合性能,促进基面晶粒往非基面取向偏转,提升了叠轧板材的力学性能,使叠轧板材由较低温度下的脆性断裂向韧性断裂转变。     

AZ31镁合金在累积叠轧焊过程中的界面焊合研究

采用扫描电境观察了AZ31镁合金在累积叠轧焊(ARB)过程中的界面焊合现象。结果表明:轧前预热温度为300℃和道次压下量为50%的累积叠轧焊工艺可以使AZ31板材获得良好的界面焊合,后续的累积叠轧焊变形可以有效改善界面焊合质量。ARB板材的拉伸断口呈现典型的延性断裂形貌,界面未形成良好焊合的部分呈现裂口焊合形貌。累积叠轧焊变形中的界面焊合过程包括:表面硬化脆性层减薄、断裂,氧化膜破碎,暴露出来的新鲜金属在轧制压力的作用下沿裂纹流动、相互接触,形成冶金结合。后续退火可以改善界面焊合质量。     

热轧工艺对AZ31镁合金组织和性能的影响

目的研究大变形量热轧、累积叠轧和普通热轧3种不同加工工艺及后续热处理对AZ31镁合金的组织及室温力学性能的影响。方法将均匀化处理后的AZ31原始样品采用大变形热轧、累积叠轧和普通热轧3种不同加工工艺制备成板材,并进行了后续热处理。利用EBSD技术和力学性能测试,解释了其组织和性能的关系。结果剧烈塑性变形工艺及适宜的热处理工艺,可使AZ31镁合金保持高强度的同时还可兼顾优良的室温延伸率。大变形量热轧工艺制备的AZ31镁合金板材的细晶组织及室温拉伸性能,可与累积叠轧等传统剧烈塑性变形工艺相媲美,屈服强度达到289 MPa,延伸率为7%。结论与普通热轧工艺制得的AZ31镁合金板材相比,大变形量热轧工艺及累积叠轧工艺制得的板材具有更高的强度和塑性。剧烈塑性变形镁合金在低温退火后获得的混晶组织,具有优良的综合力学性能,强度比形变态样品略低,而塑性与完全退火样品相同甚至更好。     

累积叠轧技术研究进展

大塑性变形工艺是制备超细晶材料的主要成形技术.其中,累积叠轧(ARB)因工序简单、成本低,对模具要求低,可连续生产大尺寸的细晶板材,而获得广泛应用.从累积叠轧后材料的组织特性、力学性能以及强化机制和界面结合机制方面梳理国内外累积叠轧工艺的研究现状.提高累积叠轧材料的塑性极其重要.制备高强度、高塑性ARB复合材料将成为后续研究热点.     

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。     

AZ31镁合金等通道转角挤压应变累积均匀性分析及组织性能研究

等通道转角挤压工艺(Equal Channel Angular Pressing,ECAP)是通过剧烈塑性变形改变微观组织结构生产超细晶粒材料的材料加工方法,工件变形的均匀性一直是ECAP 工艺过程中影响材料性能的主要原因之一.采用空间转换法实现了AZ31镁合金多道次ECAP挤压过程中有限元分析相关场量的准确传递,完成了四种不同挤压路径ECAP多道次挤压工艺的有限元模拟,获得了相应挤压件累积等效应变的分布规律.研究确定了经过四道次ECAP挤压以后等效应变累积最为均匀的挤压路径.通过微观组织观察和室温拉伸力学性能实验探讨了不同路径多道次ECAP挤压AZ31镁合金的组织性能变化规律.分析结果表明通过合适的变形路径可以获得细小而均匀的微观组织,当材料的应变累积均匀时,其力学性能也较好.     

累积叠轧制备超细晶纯铜多层板的组织和性能

本工作在室温下采用累积叠轧工艺对纯铜薄板进行1~9道次的大塑性变形加工。采用金相显微镜、双束系统FIB/SEM、TEM及拉伸试验机进行组织观察及力学性能测试,获得纯铜板累积叠轧过程显微组织演变和力学性能演变规律。结果表明:累积叠轧形成的初始界面存在微缝隙和纳米层等缺陷,其中微缝隙随着叠轧的进行而逐渐消失,最终形成冶金界面结合;纳米层由片层厚度为20~60nm的片层晶组成,并包含变形孪晶。在轧辊压缩力与剪切力的共同作用下,原始粗晶晶粒由等轴晶变成片层晶,且发生明显细化,6道次后晶粒片层厚度由退火态的~50μm细化到0.2μm左右;晶粒细化主要以位错滑移分割为主,并伴随少量的孪生;材料的硬度和屈服强度明显提高,9道次后达到最大值,硬度为137HV,约为母材的3倍;屈服强度达450MPa,约为母材的5倍;断裂延伸率在首道次剧烈下降,并在随后道次保持在5%左右。     

循环道次对高温叠轧AZ31镁合金板材组织与性能的影响

目的通过高温累积叠轧工艺制备出高强度的镁合金,并研究该过程中循环道次对AZ31镁合金板材的微观组织与性能的具体影响。方法对累积叠轧1～5次板材进行微观组织观察,并进行显微硬度的测试,得到不同板材的硬度值,通过X射线衍射分析得到不同板材的取向结果,最终进行力学性能实验,并对比分析。结果随着循环道次的增加,板材抗拉强度有明显改变。从260 MPa先增加至310 MPa,最后稳定在350 MPa左右;非基面织构比重增加;断裂伸长率先降低后升高并稳定在10%左右。结论累积叠轧工艺使得AZ31镁合金板材产生了加工硬化,并显著细化了晶粒。循环道次的增加、孪晶产生和晶界数量显著增多导致强度进一步提高。     

Microstructure and mechanical properties of Mg–Al–Zn alloy sheets severely deformed by accumulative roll-bonding

The as-rolled AZ31 Mg alloy sheets were subjected to accumulative roll-bonding (ARB) at 300 °C up to three cycles. The microstructure and macro- texture are investigated by means of optical microscopy and X-ray analysis. The mechanical properties are evaluated by micro-hardness and tensile tests. Very fine grain size of 2.4 μm could be achieved after three passes of 50% thickness reduction. The recrystallized structure was already formed after one cycle of ARB. ARB processing resulted in a significant increase of ductility and slight decrease of tensile strength of the AZ31 alloy sheet. Basal texture was notably weakened after ARB processing.     

Effect of Deformation Temperature on Microstructure and Mechanical Properties of AZ31 Mg Alloy Processed by Differential-Speed Rolling

A differential-speed rolling(DSR) was applied to AZ31 magnesium alloy sample at different rolling temperatures of 473,523,573,and 623 K with 1-pass and 2-pass operations.The microstructural evolution and mechanical properties of the deformed samples were investigated.The rolling temperature was found to be an important parameter affecting the microstructural development.After DSR at 473 K,the microstructure was more homogeneous than that obtained after deformation by equal-speed rolling(ESR).The fully recrystallized microstructures were generated after DSR at 573 and 623 K.As to mechanical properties,the yield strength(YS) and ultimate tensile strength(UTS) decreased monotonously with increasing rolling temperature.In contrast,the elongation of the DSR-deformed samples was improved as the rolling temperature increased.The strain hardening exponent(n) calculated by Hollomon equation increased with increasing the rolling temperature,which would explain an increase in the uniform elongation.     

热处理对AZ31B镁合金轧板组织和性能的影响

研究了AZ31B镁合金轧板经不同温度、时间退火后的组织和性能及其再结晶行为。结果表明,热轧板材在退火过程中主要发生再结晶;退火后,强度略有下降,但伸长率明显提高;在523K下退火,保温60min,可获得平均晶粒直径为10μm的细晶组织,其抗拉强度为258MPa,断裂伸长率为22.3%,综合性能较好。热轧态板材呈脆性准解理断裂,退火后转变为韧性断裂。     

Microstructure and mechanical properties of commercial purity titanium severely deformed by ARB process

Commercial purity titanium was deformed by accumulative roll-bonding (ARB) process up to 8 cycles (equivalent strain of 6.4) at ambient temperature. This is the first study on ultra-high straining of h.c.p. metals by the ARB process. The microstructure of the ARB-processed specimens showed two kinds of characteristic ultrafine microstructures. One was the lamellar boundary structure elongated along RD, which has been also reported in the ARB-processed cubic metals. The lamellar boundary spacing decreased with increasing ARB strain and reached about 80 nm after 5 ARB cycles. The other microstructure was the equiaxed grains having mean grain size of 80–100 nm. Such a fine and equiaxed grain structure has not yet been reported in the as-ARB-processed materials before. The fraction of the equiaxed grains increased as the ARB process proceeded, and 90% of the specimen was filled with the equiaxed grains after 8 ARB cycles. As the number of the ARB process increased, the tensile strength increased and the total elongation decreased gradually. After 6 ARB cycles, the specimen exhibited almost the same mechanical properties as that of commercial Ti-6Al-4V alloy.     

累积叠轧纯Mg/ZK60镁合金层状金属复合材料的组织与性能

采用累积叠轧技术在300℃下制备了纯Mg/ZK60 Mg合金多层复合板材。经过初始复合后,Mg层和ZK60层晶粒明显细化,随着循环次数的增加,Mg/ZK60复合板材两组元晶粒细化并不明显。两种组元的层厚随着循环次数的上升而逐渐降低,两次循环后Mg/ZK60复合板材出现波浪状组织。累积叠轧后,Mg/ZK60复合板材中Mg层和ZK60层呈现典型的轧制织构类型,{0001}基面均向轧制方向发生轻微偏转。Mg/ZK60复合板材的强度及延伸率均介于轧制态的ZK60板与Mg板之间,并随着循环次数的增加逐渐提高。Mg/ZK60复合板材室温阻尼性能和高温阻尼性能均介于纯Mg与ZK60之间,而高温下Mg/ZK60复合板材的高温阻尼则与ZK60板材变化趋势相类似。      

An investigation into the mechanical behavior and microstructural evolution of the accumulative roll bonded AZ31 Mg alloy upon annealing

The effect of annealing treatments on the room temperature mechanical properties (in the range of 23–27 °C) of an AZ31 magnesium alloy processed by accumulative roll bonding (ARB) have been investigated. The evaluation of mechanical properties was carried out using shear punch testing (SPT) method. The reliability of the method was verified through application of a well calibrated uniaxial tensile testing machine and the related correlation factors were adapted. The texture evolution was also studied upon annealing. The results showed that the room temperature strength of the ARB processed AZ31 alloy is increased by increasing the annealing temperature up to 350 °C. At temperatures above 350 °C, the deterioration of mechanical properties was taken place as a result of rapid grain growth.     

Microstructure development and texture evolution of ME20 sheets processed by accumulative roll bonding

Magnesium alloy ME20 sheets were produced by accumulative roll bonding (ARB) up to 8 cycles. The rolling microstructure was significantly refined during the first 2 cycles and remained homogeneous up to 6 cycles. After 8 cycles (ε ~ 6.4) the homogeneous equiaxed microstructure was replaced by a very fine shear band microstructure. With increasing ARB cycles, the texture intensity of basal poles decreased leading to a higher sheet tensile strength but with decreasing ductility.     

初始晶粒尺寸对高温交叉轧制镁合金板材组织和力学性能的影响

目的 揭示晶粒尺寸对多道次高温交叉轧制AZ31镁合金板材组织和力学性能的影响规律及机制.方法 通过对不同初始晶粒尺寸的镁合金板材进行高温交叉轧制变形及热处理,获得不同状态的镁合金板材,采用金相显微分析、X射线衍射(XRD)分析及室温拉伸实验等手段研究镁合金板材的晶粒组织(形态、尺寸、取向)及力学性能.结果 经过多道次交叉轧制后,不同初始晶粒尺寸的板材均发生了孪生现象,但粗晶板材的晶粒尺寸仍明显大于细晶板材.退火处理后,细晶退火态板材组织均匀性较好,而粗晶退火态板材的组织虽有细化,但并不均匀.随着交叉轧制次数的增加,两种板材内非基面取向晶粒都有所增加.退火后粗晶板材中非基面取向晶粒更多.结论 晶粒细化和晶粒取向强化导致退火后的交叉轧制细晶镁合金板材具有更高的强度.粗晶板材伸长率较高主要与其具有更多的非基面取向晶粒有关.     

Effect of 1.5 wt% tin addition on the properties of AZ31 magnesium alloy

In this paper, 1.5 wt%Sn was added to the AZ31 magnesium alloy aiming at improving the mechanical properties by using a low cost alloying element. Both alloys were prepared in the cast/heat treated (HT), rolled at 350 °C, rolled/heat treated at 400 °C and extruded at 350 °C. The results indicate that with addition of tin an improvement was obtained in both tensile strength and ductility of the AZ31 alloy in the cast/heat treated and in the extruded conditions. The yield and ultimate tensile strengths reached 98 MPa and 224 MPa respectively with 14 % elongation in the cast/heat treated condition while in the extruded condition these values were 212 MPa and 286 MPa with 20 % elongation. The tensile strength was even higher after rolling reaching 315 MPa for AZ31 with tin addition; however, as the material temperature during the last passes has decreased to relatively low values, the % elongation decreased to 1 %. After heat treatment at 400 °C for 2 hours the % elongation was restored and reached 12 %; this was accompanied by a decrease in tensile strength which reached 276 MPa. The results are discussed in relation to the microstructure evolution including grain size, phase identification, and volume fraction of phases.     

Effects of annealing treatment on the ratcheting behavior of extruded AZ31B magnesium alloy under asymmetrical uniaxial cyclic loading

The objective of this investigation is to study the effects of annealing treatment on the ratcheting behavior of extruded AZ31B magnesium alloy. First, the microstructures and monotonic tensile properties of the extruded and annealed alloys were assessed. The results showed that the grain size increased slightly with increasing annealing time until an annealing time of 6 h after which abnormal grain growth happened. Accordingly, the ultimate tensile strength of the Mg alloy decreased with increasing annealing time, while the tensile yield strength and elongation percentage of the Mg alloy increased with annealing time until the annealing time reached 2 h. The cyclic softening/hardening behavior of the annealed AZ31B Mg alloy was similar to that of the extruded alloy: first an apparent cyclic softening was observed, then a cyclic hardening occurred, and finally a stable state was reached. The annealing treatment delayed the occurrence of the cyclic hardening. It was also shown that the effects of the annealing time on the ratcheting strain of the Mg alloy depended of the loading path.