Microstructure evolution of AZ31 Mg alloy during change channel angular extrusion

Microstructure evolution of AZ31 Mg alloy during change-channel angular extrusion (CCAE) was investigated. The grains of AZ31 Mg alloy were refined significantly from 500 mm to 15 mm after CCAE deformed at 523 K. Dislocations were induced at the initial stage of extrusion and they rearranged themselves to form dislocation boundaries and sub-grain boundaries during deformation. When the specimen through the horizontal change channel with the strain increased, the sub-boundaries evolved to high angle grain boundaries (HAGB). The process of grain refinement can be described as continuous dynamic recovery and recrystallization (CDRR).     

Constitutive analysis of AZ31 magnesium alloy plate

The plastic deformation simulation of AZ31 magnesium alloy at different elevated temperatures (from 473 to 723 K) was performed on Gleeble-1500 thermal mechanical simulator at the strain rates of 0.01, 0.1, 1, 5 and 10 s-1 and the maximum deformation degree of 80%. The relationship between the flow stress and deformation temperature as well as strain rate was analyzed. The materials parameters and the apparent activation energy were calculated. The constitutive relationship was established with a Zener-Holl...     

大规格AZ31B变形镁合金坯料的高纯净化制备

为了实现高纯大规格AZ31B变形镁舍金坯料工业化生产,通过对原辅料的控制,采用双联气体保护熔炼、电磁泵转移和液压式半连续铸造,并严格控制熔炼温度、浇铸温度、浇铸水压和浇铸速度,生产出了质量较高的变形镁舍金坯料．经检测,化学成分符舍ASTM—B93标准,内部组织和纯净度符合Q／QC011—2006规定,     

间断变形工艺提高AZ31镁合金超塑性的研究

研究间断变形工艺对AZ31镁合金超塑性的影响。结果表明,当温度为400-440℃、应变速率小于5×10^-4s^-1时,间断变形工艺可以显著提高AZ31镁合金的超塑性。计算了空洞体积分数与空洞数量的关系。结果表明,空洞体积分数与空洞数量呈正比。对拉伸试样断口形貌的分析表明,间断变形减少了空洞数量,因而减小了空洞体积分数,提高了超塑性伸长率。     

Examination of dynamic recrystallization during compression of AZ31 magnesium

This study aimed to investigate dynamic recrystallization (DRX) behavior during compression of magnesium alloy AZ31. Cylinder samples were cut from the extruded rod and hot rolled sheet AZ31 for compression test. The samples were compressed using a Gleeble 1500D at a temperature of 300℃ and a strain rate of 0.01 s-1. Grain orientations and misorientation angles across grain boundaries for the tested samples were obtained by using electron backscatter diffraction (EBSD) technique. The results showed that strong basal texture was observed after 50% compression (ε = 0.69) on both the extruded and hot rolled samples, which have different initial textures. It was observed that with increased strain, DRX grains gradually rotated to basal orientation, and grain boundaries with misorientation angle of near 30° was formed in the samples. At the strain of 0.69, a high fraction of high-angle (> 60°) bounda-ries was present in the extruded sample, whereas almost no high angle boundaries were observed in the hot rolled sheet sample.     

As-extruded AZ31B magnesium alloy fatigue crack propagation behavior

The fatigue crack propagation rate of as-extruded AZ31B magnesium alloy was studied. Compact tension [C(T)] of the notch direction parallel (T-L), vertical (L-T), and inclined at 45o to the extrusion direction was investigated. The experimental results indicate that the crack propagation direction is parallel to the extrusion direction for T-L and L-T specimens, whereas the specimen inclined at 45o has an angular deflection of 9° to 11° toward the extrusion direction. The T-L specimen has the fastest fatigue crack propagation rate, and the L-T specimen has the slowest rate, the fatigue crack propagation rate of the specimen inclined at 45o is between the two directions. The crack tip propagates by both transgranular and intergranular fractures. Fatigue fractures consist of cleavage plane or quasi-cleavage and are brittle fractures. The fatigue striation occurs for specimens inclined at 45o and its size is 3-15 μm.     

AZ31B变形镁合金板材的TIG焊接

采用TIG焊对5 mm厚AZ31B挤压镁合金板材进行了焊接试验。采用万能拉伸试验机、金相显微镜、扫描电子显微镜和显微硬度仪等分析测试手段对焊接接头的组织、力学性能以及断口形貌等进行了分析。探讨了焊接电流对焊接接头的组织及力学性能的影响,揭示了不同焊接电流下焊接接头的断裂机制。结果表明,采用TIG焊焊接5 mm厚AZ31B镁合金板时,开X型坡口,采用双面焊接双面成型工艺,在130~145 A焊接电流及合适焊接速度条件下,能得到表面成型良好的焊接接头。当正反面焊接电流均为145 A时,AZ31B镁合金板焊接接头的抗拉强度达到最大值248.6 MPa,约为母材强度的84.0%。AZ31B镁合金板焊缝区显微硬度比母材区稍有所下降,热影响区显微硬度下降比较严重。当焊接电流为145 A时,AZ31B镁合金板焊接拉伸断口有大量韧窝,属韧性断裂。     

MgCO_3对AZ31镁合金晶粒的细化

研究了MgCO3对AZ31镁合金凝固组织的影响。结果表明:随着MgCO3的增加,合金中的β-Mg17Al12相由晶内分布变为晶间分布。在AZ31中添加0.6%的MgCO3,于760℃时保温10min,细化效果最佳。α-Mg晶粒的尺寸由基体合金的570μm降至100μm,降低幅度约为82.5%,抗拉强度提高了57.9%,延伸率约提高了11.1%。通过能谱分析,结合能计算及自由能计算证实,细化机理是MgCO3反应后生成的部分Al4C3质点作为异质核心细化晶粒。多余的Al4C3质点钉扎晶界阻碍晶粒长大。Al元素随固/液界面前沿被快速推至晶界,生成沿晶界生长的β-Mg17Al12相,起到进一步固定晶界的作用。合金元素的分布均有改变。     

AZ31B镁合金和6065铝合金动态压缩行为数值模拟

为了研究帽状试样AZ31B镁合金和6065铝合金在动态压缩变形过程中的温度、应力与应变演变规律,采用Johnson-Cook本构方程和累积塑性损伤方程进行了数值模拟,运用有限元软件ANSYS/LS-DYNA模拟了AZ31B镁合金和6065铝合金帽状试样的动态变形过程.结果表明,两种合金的裂纹萌生和扩展过程相似,局域化变形带内塑性应变由内向外对称分布.相比于AZ31B镁合金,6065铝合金的塑性应变影响区域更为狭小,其应变和应变率硬化效果更强.6065铝合金的变形温度能够达到其动态再结晶临界点,因而易于绝热剪切带的形成.     

粗晶粒铸轧AZ31镁合金的高温拉伸性能

研究了具有较大晶粒尺寸铸轧态AZ31镁合金的高温拉伸性能。通过热处理获得晶粒尺寸d=27．8μm的板材,对不同试样,在温度分别为300,350,400,450℃恒温条件下,以10^-3s^-1和10^-3s^-1恒定拉伸速率对试样进行拉伸至失效实验。结果表明,粗晶粒AZ31镁合金在450℃和10^-3s^-1条件下达到最大的延伸率106．7％。拉伸试样断口形貌的分析表明,450℃时出现丝状物质是合金出现液态zn的结果。少量的液相可以释放应力集中和协调此时的变形过程。与细晶粒铸轧态AZ31相比,在拉伸条件相同和晶粒尺寸不同的情况下,粗晶粒的塑形较低,其原因是晶界滑移在变形时所作贡献少。     

Superplastic Deformation Behavior of Hot-rolled AZ31 Magnesium Alloy Sheet at Elevated Temperatures

1IntroductionAs a typical wrought magnesiumalloy,AZ31alloyhas a wide prospect for applications inthe fields of auto-mobiles,electronic appliances and aeronautic facili-ties[1,2].However,due to the hexagonal close-packed(HCP)structure of magnesium,the ductility of AZ31al-loy at roomtemperature is rather poor,which greatly re-stricts its applications in structural fields[3-5].Owing tothe activation of non-basal slip system[6],the ductility ofMg alloycan be significantlyimproved at elevatedtem…     

晶粒大小对AZ31镁合金绝热剪切敏感性的影响

为了研究晶粒尺寸对镁合金绝热剪切敏感性的影响,采用等通道转角挤压(ECAP)技术对AZ31镁合金进行了不同程度的晶粒细化并采用分离式Hopkinson压杆对细化后的AZ31镁合金试样进行了动态剪切试验.采用光学显微镜、扫描电子显微镜、透射电子显微镜和维氏硬度计,分别对冲击压缩后的AZ31镁合金试样进行了组织观察和硬度测试.结果表明,晶粒越小,AZ31镁合金的绝热剪切敏感性越弱.在对绝热剪切带及其周围组织进行维氏硬度测量时发现,剪切带内细小晶粒区的硬度明显高于其周围组织的硬度.     

Modeling texture development during cold rolling of IF steel by crystal plasticity finite element method

With the consideration of slip deformation mechanism and various slip systems of body centered cubic (BCC) metals,Taylor-type and finite element polycrystai models were embedded into the commercial finite element code ABAQUS to realize crystal plasticity finte element modeling,based on the rate dependent crystal constitutive equations.Initial orientations measured by electron backscatter diffraction (EBSD) were directly input into the crystal plasticity finite element model to simulate the development of rolling texture of interstitial-flee steel (IF steel) at various reductions.The modeled results show a good agreement with the experimental results.With increasing reduction,the predicted and experimental rolling textures tend to sharper,and the results simulated by the Taylor-type model are stronger than those simulated by finite element model.Conclusions are obtained that rolling textures calculated with 48 {110}<111>+{ 112}<111>+{123}<111> slip systems are more approximate to EBSD results.     

磁场电流对AZ31镁合金组织与性能的影响

为了改善AZ31镁合金的综合性能并提高其利用价值,通过在AZ31镁合金整个凝固过程施加旋转磁场制备镁合金管坯.通过改变磁场电流对磁场与自然凝固条件下获得的AZ31镁合金铸锭的微观组织及力学性能进行了观察与测试,研究了磁场电流对AZ31镁合金显微组织和力学性能的影响.结果表明,随着磁场电流的增大,合金晶粒逐渐细化,晶粒内部出现较多的孪晶,且β-Mg17Al12相逐渐减少并细化.磁场电流越大,AZ31镁合金的力学性能越好.当磁场电流为150 A时,AZ31镁合金的抗拉强度为194 MPa,屈服强度为98 MPa,伸长率为14. 8%,与自然凝固状态相比分别提高了23. 6%、32. 4%和57. 4%.     

真空熔炼时AZ31中Mg,Zn挥发行为及组织与性能

在分析合金元素的挥发行为及机理的基础上,对金属粉尘进行了分析.观察了合金的铸态微观组织,并着重讨论了提高AZ31力学性能的途径.研究结果表明:真空熔炼过程中,合金熔体中元素的活度影响其挥发速率;真空条件下合金中存在的气体量降低,夹杂物分解,提高了合金的纯度,使合金显现出本身的特性;AZ31的铸态抗拉强度达210 MPa,比熔炼前提高了82.6%;延伸率为5%,提高了31.5%.     

退火处理对单道次轧制镁合金薄板组织的影响

变形镁合金因其优越的性能越来越受到国内外研究者的重视。采用单道次轧制的方法轧制出厚度为0.4 mm的AZ31镁合金薄板。对轧制后的薄板在不同温度、不同保温时间下进行退火处理,分析薄板在不同退火条件下的微观组织变化。结果表明:薄板经退火处理后组织变得更加细小均匀,平均晶粒尺寸为5μm。退火温度和保温时间共同影响着薄板的晶粒度,在320℃退火并保温80 min时平均晶粒度最小,仅有4.02μm。     

AZ31镁合金在不同挤压比和挤压温度下的织构演变

采用工业挤压机研究了挤压比和挤压温度对AZ31镁合金织构的影响.结果表明,在相同的挤压温度下,随挤压比增加,以{01(-1)0}面织构为代表的变形织构由强到弱;而以{06(-6)1}、{02(-2)1}面为代表的再结晶织构由弱到强.主要织构组分在挤压比为16处形成拐点,形变织构降至最低,随后再结晶织构逐渐增强,表明在拐点附近再结晶完成.挤压比相同时,低温度变形的织构组分以{01(-1)0}面形变纤维织构为主.当挤出温度增至258℃时,达到完全动态再结晶,温度再增高将形成高漫散度的{01(-1)0}再结晶织构.     

AZ31B镁合金应变诱发半固态组织观察

采用AZ31B镁合金挤出材,在573K进行28％-30％预变形加工,然后在863—893K经过不同保温时间进行等温球化处理,观察了试样不同区域的组织,考察了温度及保温时间对组织的影响,得到了具有圆整固相颗粒的半固态组织．实验结果表明：适当提高球化处理温度,有利于加速球化过程,以获得细小圆整半固态组织;延长保温时间固相分数降低,但幅度不大,并发生颗粒不规则化;在同一个试样上,由于部位不同,变形程度不同,所得半固态材料的固相率不同．讨论了半固态组织的形成机理,分析认为预变形后,半固态组织形成过程包括再结晶、晶粒长大阶段,受溶质、空位扩散控制的半固态组织形成阶段,受液-固界面张力作用的固相颗粒圆整化阶段．开始形成半固态组织阶段,扩散占主导地位,在进一步球化过程中,界面张力占主导地位．     

异步轧制对AZ31镁合金板材组织和性能的影响

主要研究了异步轧制对AZ31镁合金板材的金相组织和性能的影响,以探讨提高AZ31镁合金板材塑性变形能力的途径。结果表明,由于异步轧制时板材的变形量比常规轧制时的要大,其动态再结晶进行的比较完全,因此异步轧制有利于AZ31镁合金板材晶粒的细化与均匀化;并且改变异步轧制的工艺条件,能够在一定程度上改善镁合金板材中的金相显微组织和板材中的{0001}基面织构取向,使织构得到软化,显著提高AZ31镁合金板材的伸长率,轧向和横向都大约提高了33%,这说明异步轧制可以提高镁合金的塑性变形能力以及二次成形性能。     

异步SLSU对AZ31镁合金板材组织和性能的影响

主要研究了异步轧制对AZ31镁合金板材的金相组织和性能的影响，以探讨提高AZ31镁合金板材塑性变形能力的途径。结果表明，由于异步轧制时板材的变形量比常规轧制时的要大，其动态再结晶进行的比较完全，因此异步轧制有利于AZ31镁舍金板材晶粒的细化与均匀化；并且改变异步轧制的工艺条件，能够在一定程度上改善镁舍金板材中的金相显微组织和板材中的{0001}基面织构取向，使织构得到软化，显著提高AZ31镁合金板材的伸长率，轧向和横向都大约提高了33％，这说明异步轧制可以提高镁合金的塑性变形能力以及二次成形性能。