基于FEM的战地车用AZ31镁合金板材ICAE工艺研究

细化晶粒、提高金属综合性能是当前战地车用AZ31镁合金板材塑性成形工艺迫切需要研究的内容。提出了AZ31镁合金板材的减径通道转角(Ironing channel angular extrusion,ICAE)挤压成形工艺。采用数值模拟结合理论分析的方法,对ICAE工艺下200 mm×2 mm的AZ31镁合金板材微观组织演化规律进行了研究。结果表明:ICAE通过晶粒破碎和动态再结晶可以显著细化AZ31镁合金晶粒,板材平均晶粒尺寸可达15μm。     

AZ31镁合金超塑性及其变形机制图

在温度为400～440 ℃、应变速率为10-2～10-4 s-1范围内,研究挤压态AZ31镁合金的超塑性.结果表明,当应变速率较高时,颈缩是超塑性断裂的主要原因.温度越高,应变速率敏感指数m值越大, AZ31镁合金的超塑性伸长率越高.当应变速率较低时,空洞扩张是影响超塑性断裂的主要原因,温度越高,超塑性伸长率越低.研究了超塑性变形机理,建立了超塑性变形机制图,结果表明,温度为400 ℃或420 ℃、应变速率较低时,AZ31镁合金的超塑性变形属于溶质拖曳的位错蠕变机制;当应变速率较大时,属于攀移控制的位错蠕变机制.温度为440 ℃时,AZ31镁合金的变形机制符合晶格扩散控制的位错蠕变.     

AZ31镁合金铸轧板材的热变形空洞演化行为

通过疲劳试验机/扫描电镜的原位观察、以及扫描电镜/图像分析软件的定量分析,研究AZ31镁合金铸轧板材热变形过程中的空洞演化行为.结果表明:镁合金板材热变形过程中,空洞首先在晶界尤其是在三叉交界处形核,随后不断长大和聚合,导致材料断裂;空洞的长大具有方向选择性,与拉伸轴方向垂直的空洞容易长大.空洞长大机制的理论模型计算与试验结果对照表明:孔径小于2 μm小空洞的圆度系数接近1,其主要长大机制为晶界扩散;孔径大于2 μm大空洞的圆度系数和取向角均比较分散,其主要长大机制是塑性变形.     

AZ31B镁合金板材超塑性变形与断裂机理研究

研究了工业态热轧AZ31B镁合金板材的超塑性及其变形机制,在应变温度为723K,应变速率为1×10-3s-1的试验条件下,其最大断裂伸长率达到216%,应变速率敏感性指数达0.36。研究结果表明:晶界滑动(GBS)是工业态热轧AZ31B镁合金超塑性的主要变形机制,变形初期有动态再结晶发生,断裂是由晶界处形成的空洞不断长大、连接而引起的。     

搅拌摩擦加工AZ31细晶镁合金超塑性行为研究

借助搅拌摩擦加工工艺制备了AZ31细晶镁合金,研究对比了原始母材和各种晶粒尺寸细晶镁合金的超塑性行为。结果表明：AZ31板材平均晶粒尺寸由7.67μm细化到0.94μm~3.21μm。在450℃,应变速率5×10-4/s-1时原始母材最大延伸率为630%,搅拌摩擦加工后的材料最大延伸率为405%,说明晶粒尺寸与超塑性性能没有线性关系。超塑性变形机制主要是晶界滑移,孪生对变形也有一定影响。断裂机制是晶间微小空洞的形成、长大和连接。     

镁合金超塑性与损伤研究的现状

本文介绍了镁合金材料的超塑性研究现状和发展方向 ,以及连续损伤力学基于含内变量热力学势函数建立的金属超塑性变形损伤演变方程 ,并从微损伤演化物理规律及统计细观损伤力学出发 ,建立超塑性材料空洞损伤的演化方程 ,预测材料超塑性变形失稳和成形极限     

搅拌摩擦加工AZ31细晶镁合金超塑性行为

借助搅拌摩擦加工工艺制备了AZ31细晶镁合金,研究对比了原始母材和各种晶粒尺寸细晶镁合金的超塑性行为。结果表明:AZ31板材平均晶粒尺寸由7.67μm细化到0.94~3.21μm。在450℃,应变速率5×10~(-4) s~(-1)时原始母材最大延伸率为630%,搅拌摩擦加工后的材料最大延伸率为405%,说明晶粒尺寸与超塑性性能没有线性关系。超塑性变形机制主要是晶界滑移,孪生对变形也有一定影响。断裂机制是晶间微小空洞的形成、长大和连接。     

镁合金AZ31常温下的塑性变形行为

通过挤压制取镁合金A231镁合金板坯,常温下进行轧制,研究其塑性变形行为。考察了镁合金AZ31组织和轧制工艺参数对其常温下塑性变形能力的影响。结果表明,晶粒度和道次加工率是影响镁合金AZ31常温塑性变形能力的重要因素。当挤压板坯晶粒度为10μm时,板材轧制变形由脆性转变为塑性。总加工率越大,晶粒越细,塑性越好。合理分配道次加工率可使总加工率增大。     

不同加工路径对汽车用AZ31B镁合金薄板冷冲性能的影响

对AZ31镁合金1.5 mm厚板材进行了不同路径等通道角挤压变形,研究了其对AZ31B镁合金板材冷冲性能的影响。结果表明,改变等通道角挤压路径不仅能够细化晶粒,更能够通过弱化其基面织构提高镁合金冷冲成形性能。与单向ECAP(路径A)相比,180°翻转挤压(路径C)后的板材冷冲性能最高。而对于每道次90°翻转(路径D),板材各个方向上的冷冲高度基本一致,说明变换等通道角挤压路径有利于降低镁合金板材的各向异性。     

织构化AZ31B镁合金在不同温度下的成形极限(英文)

通过单向多道次弯曲(RUB)来改善商业AZ31B镁合金的织构,所有的试样都沿轧制方向制备。在室温、100、200和300°C下,通过延展成形实验研究AZ31B镁合金的成形极限图(FLDs)。与原始板材相比,在室温和100°C下,FLD中具有倾斜织构的AZ31B镁合金的最低极限应变分别提高了79%和104%。织构也影响FLD中成形极限曲线(FLC)的范围。当温度高于200°C时,两种板材的FLCs几乎重合。(0002)基面织构强度的削弱不仅有助于室温成形性能的提高,而且有助于中低温度成形性能的提高。随着温度的升高,织构对FLDs的影响减弱。     

SuperplaSticity and superplastic instability of AZ31B magnesium alloy sheet

1 Introduction Due to its light mass, high specific strength, good damping characteristics, strong thermo-conductivity and electromagnetic shielding, magnesium alloys have been regarded as “the green material” with the greatest application potential in …     

Superplastic Response of Continuously Cast AZ31B Magnesium Sheet Alloys

Magnesium sheet is typically produced for commercial applications with the traditional DC-ingot casting method. As a result of the hexagonal close-packed crystallographic structure in magnesium, multiple rolling passes and annealing steps are required to reduce the thickness of the ingots. Thus, high fabrication costs characterize the creation of magnesium sheet suitable for common forming operations. Recently, continuous casting (CC) technology, where molten metal is solidified directly into sheet form, has been applied to magnesium alloys; this method has shown the potential to significantly reduce the cost of fabricating magnesium sheet alloys. In order to understand the viability of the CC process, a study was conducted to investigate the superplastic potential of alloys produced by this method. This study focused on AZ31B Mg that was continuously-cast on twin-roll casters from three different suppliers. These three materials were compared with a production DC-cast AZ31B alloy in terms of microstructure, elevated-temperature tensile properties, and superplastic forming response. The data from this study found that microstructural features such as grain size and segregation can significantly affect the forming response. Additionally, the CC alloys can have equivalent or superior SPF response compared to DC-cast alloys, as demonstrated in both elevated temperature tensile tests and superplastic forming trials using a rectangular pan die.     

Promotion mechanism of the pulse current on the superplastic deformation of AZ31 magnesium alloy

The effects of pulse current on the superplastic deformation of AZ31 magnesium alloy with different microstructures were examined. The results of TEM analysis showed that the dislocation movement was mainly glide, and the dislocation lines were approximate parallel with few dislocation tangles observed, which indicated that the dislocation movement was promoted during the deformation, and therefore the formability of the coarse-grained AZ31 magnesium alloy was enhanced by the pulse current. This effect was also indicated by the asymmetrical contour of the free bulging sample, which was observed in the unidirectional pulses auxiliary equi-biaxial tensile test of coarse-grained alloy. In addition, the phenomenon of the restrained cavity growth caused by the thermoelectrical effect of the pulse current was discovered and studied.     

Using X-ray microtomography to evaluate cavity formation in a superplastic magnesium alloy processed by equal-channel angular pressing

The magnesium AZ31 alloy exhibits excellent superplastic properties after processing by equal-channel angular pressing (ECAP) and testing in tension at a temperature of 623 K. Experiments show that there is an increase in the elongations to failure with increasing numbers of passes in ECAP. X-ray microtomography was used to obtain detailed information on the morphologies of cavities developed during superplastic flow and the results were analyzed in terms of the different possible cavity growth mechanisms. The results show that superplastic elongations are attained in this alloy because the finer grain structure introduced by ECAP is associated with lower flow stresses in tensile testing at elevated temperatures and this leads to a reduction in the rate of growth of internal cavities.     

背压对AZ31镁合金板材快速气压胀形的影响

利用快速气压胀形实验,研究背压对AZ31镁合金轧制板材胀形时空洞体积分数、胀形高度和壁厚分布的影响。研究结果表明,在胀形温度为350℃的工艺条件下,胀形件顶部在无背压和加载背压时,空洞的比率分别达到了21%和16%。在相同的应变下,加载背压时获得的胀形件中的空洞比率小于无背压时的空洞比率。背压的加载,能有效降低板材中空洞的分布比率,提高板材的胀形高度,进而提高成形极限。     

退火温度对大变形热轧AZ31镁合金板材力学性能的影响

采用热挤压态AZ31变形镁合金板坯,研究了退火温度对大变形热轧AZ31变形镁合金板材力学性能的影响.结果表明:随着退火温度的升高,变形镁合金板材的抗拉强度和屈服强度减小,伸长率呈线性增加趋势,硬度和杯突值均降低.变形镁合金板材的力学性能与其晶粒尺寸和组织均匀性密切相关.     

LZ91镁锂合金板材的超塑性气胀成形研究

本文利用热拉伸实验、气胀成形实验、金相分析和扫描电镜观察,研究LZ91镁锂合金板材的超塑性、气胀成形性能及其组织结构。结果表明:在热拉伸变形温度为573 K、应变速率为0.001 s-1时,其伸长率可达343.7 %,应变速率敏感指数为0.697,轧制态的LZ91合金板材表现出优良的超塑性;在胀形温度573 K,胀形气压0.06 MPa条件下,板材成形高度为51.14 mm,高径比达1.279,说明该镁锂合金板材具有良好的超塑性成形潜力;在热拉伸变形和超塑性气胀成形过程中,均有动态再结晶现象产生,可有效提高该合金的塑性成形能力;在拉伸断口和胀形件破裂处断口均存在典型的超塑性空洞形貌特征,说明两者的主要变形机制均为晶界滑移,且合金超塑性失效的主要原因是空洞的长大和连接。     

AZ31B镁合金薄板的单向拉伸行为实验研究

在Gleeble-3500热模拟试验机上对AZ31B镁合金薄板(0.6 mm)拉伸试样在100～350℃的温度范围和1×10-1～1×10-3s-1的应变速率范围内进行了的单向拉伸实验,根据实验结果对AZ31B镁合金薄板的力学性能进行了分析.结果表明:AZ31B镁合金薄板在较低变形温度100～150℃时,应变速率对流动应力的影响不大;相比之下应变速率对AZ31B镁合金的断裂伸长率却有一定的影响,提高应变速率会降低材料的伸长率;在较高变形温度(200℃以上)时,应变速率对流动应力的影响比较明显,表现出显著的应变速率敏感性.     

AZ31镁合金的等温挤压及其力学性能分析

等温挤压是镁合金材料的重要加工方法,它能改善制品的质量,提高制品的力学性能。研究了等温挤压AZ31镁合金材料的力学性能。结果表明：等温挤压显著地提高AZ31镁合金的强度、硬度,但当变形程度达到82％以上时,其强度不再增加,反而下降。材料的硬度有方向性。     

AZ31镁合金铸轧和常规轧制板的变形组织及形变特征

在变形温度为150～400 ℃、应变速率为0.3～0.000 3 s~(-1)条件下,在Gleeble1500热模拟机上采用等温拉伸试验对AZ31镁合金铸轧和常规轧制板的高温塑性及组织演变进行研究.结果表明:两种AZ31镁合金板的峰值应力和峰值应变均随着变形温度的降低和应变速率的增加而逐渐增大.铸轧板的应变硬化指数和应变速率敏感系数均大于常规轧制板的.在高温低应变速率变形条件下,铸轧板的晶界滑移引起的空洞尺寸、体积分数和密度均大于常规轧制板的.低应变速率下拉伸变形后的动态再结晶晶粒尺寸随温度的升高逐渐增加;不同变形条件下铸轧板的晶粒尺寸均小于常规轧制板的;再结晶晶粒尺寸和Z参数呈幂律关系.