材料成型及控制工程外文文献翻译--AZ31镁合金在高温下的吹塑成型.docx

毕业设计（论文）的外文文献翻译原始资料的题目/来源： Blow forming of AZ31 magnesium alloys at elevated temperatures/ORIGINAL RESEARCH 翻译后的中文题目： AZ31镁合金在高温下的吹塑成型 院 （系） 材料科学与工程学院 专 业 材料成型及控制工程 中文翻译AZ31镁合金在高温下的吹塑成型1.摘要：本文研究和报道了关于AZ31B镁合金商业片在高温下的成形行为。实验分两个阶段进行。第一阶段是分析自由胀形实验，第二阶段是分析板材填充封闭模具的能力。施加不同的压力和温度，用标本圆拱高度表征参数，在相同时实验中，使用分析的方法来计算应变速率敏感指数。因此适当的成形参数如温度和压力，对于随后的成形实验是有用处的。第二阶段中，在带有棱形空腔的密闭模具中进行成形实验。同时分析了相关的过程参数对成形结果中壁厚填充、最终样品上圆角半径及分布的影响。闭模成形实验证明：如果工艺参数选择适当，所研究的商业镁板可成形复杂的几何形状。2.关键词：吹塑成形、材料特性、AZ31镁合金3.简介在众多结构材料中，镁合金以其低比重得到了行业厂家越来越多个兴趣，镁合金在具有最低的密度，在轻量化上也有很高的潜力，尤其是在移动正在使用运动部件的领域。在这些应用中，越来越多地为轻质合金材料，尤其是传统的成形方法无法快速有效的成形镁合金等合金，使得超塑性成形（SPF）成为一种有吸引力的成形方法。事实上，具有极其复杂形状的轻量化部件可以由具有超塑性的单层板通过超塑性成形制造。轻金属合金如铝、钛和镁，有些难以在传统的成形条件下成形，吹塑成形（BF）的应用随之越来越多。吹塑过程主要是将坯料放入模具型腔中，并在其上施加成形气体（如空气、氩气）。相比基于成形操作的流体，在高温成形的区域，气体的耐热性为实现更高的温度提供了可能1。该气体可完全替代传统冲压工序中的驱动冲头，并且允许具有高细节层次的不同种类材料的变形。在过去，吹塑成型的理念主要应用在传统的玻璃吹制上，它的主要原理是在材料温度高于其软化点后成形。目前，BF的原理已被广泛应用到塑料的制造上。这个过程进行的金属板料成形相比传统的成形方法潜力是显著的。它有如下优点：（i）在具有高细节层次的单一操作中成形大而形状复杂的组件；（ii）他们用近似网状的制造方法大大减少了后续的成本和在装配操作上花费的时间；（iii）无需人力损耗；（iv）成品有更高的尺寸精度；（v）回弹对成形部分影响小。然而，金属的超塑性吹塑成形并没有在工业上得到广泛的应用，因为其原材料和生产过程成本较高，这使得它的竞争力要比其他的传统技术弱。为了克服这些缺点，高应变速率超塑性和其他技术比如快速塑料成形应用而生，并且为实现大批量生产一直在改进。成功实施QPF技术需要一个远离小批量假设的转换，这种假设与之前应用在航空航天和利基汽车产品的BF技术是相关联的。另一方面，原材料的准备更加苛刻：控制极小平均晶粒尺寸的显微结构也是有要求的2,3。在这项工作中，分析了在高温下通过BF技术的装置一块商业镁板的成形行为。所使用的刚发包括两个方面：（i）通过胀形测试得出的第一相表征；（ii）第二阶段在封闭模具中成形过程的分析。该工作主要目标是结合BF技术分析镁合金在工业生产过程中的应用潜力。这些合金已经显示出在高温下具有超塑性4,7。最终目标是看这种成形技术对商业开发的影响，一旦工艺参数的优化有了显著的成果，首先可是实现循环时间的减少。4.实验装置：在实验室规模的设备上已经进行了材料特性和封闭模具成形测试，这个设备嵌在INSTRON万能材料试验机的圆筒形裂解炉中。设备包括：（i）一个压边器，（ii）具有多个不同型腔的凹模，来满足不同的成形条件，（iii）连通氩气缸的供应气体的气动回路，在靠近成形腔室应有成比例电磁阀和钢管，在低温地方有灵活的聚氨酯管，（iv）具有电子控制器的电炉，为补偿热扩散，需在上部、中部、下部设置三种不同的温度，（v）监测板材和工具热条件的热电偶，（vi）一个传感器用于测量在胀形试验期试样的圆顶高度（vii）采集I/O设备上温度，压力，压边力数据的PC机，可以用来监控和管理。对于材料特性，胀形试验在一个直径为45mm的圆筒形模腔中进行，板材在其中可以自由扩散。在整个实验过程中通过数字采集的位置传感器信号检测试样的圆拱高度。设备上的更多详情可见参考文献8。在闭模成形试验中，使用的是具有14mm深棱柱空腔的模具。该空腔截面为方形，边长为40mm，两侧之间的圆角半径为5mm。设备示意图如图1。图1 封闭模具成形试验的试验装置5.材料特性商业AZ31B镁合金板材在收获状态中已经得到测试。该材料未经机械和热处理；板材在退火条件下已被压紧，平均晶粒尺寸为153m，厚度0.75mm。 关于材料的超塑性特性，拉伸试验通常是在不同的温度和应变速率条件下进行，目的是为了得到材料具有最高断裂伸长率的最佳条件。这个可以通过拉伸试验测量断裂伸长率和跳应变速率实验测量应变速率敏感性指数得到9。一些学者证明：当晶界滑移（GBS）为主要变形机制时，应力和应变条件对材料特性影响不大10。其他学者也证明了单轴拉伸应力和应变条件不能有效地获得材料的参数，因为成型过程中板材存在这样一个现象，与模具相互作用，然后再经过一定的应力应变条件，结果完全不同。此外，镁合金具有晶粒粗大的趋势，并且一些例子证明GBS不能作为主要的变形机制11。同时，在超塑性条件下进行单轴拉伸试验必须合理设计实验装置和试样几何形状。一些标准的存在，如ISO20032和ASTM E2448给试验步骤和设备以很好的指示。在超塑性条件下，拉伸试验的显著优势是在试验过程中，有可能可以是更加精确的控制应变速率，但是另一方面，可以说：试样的切割精度必须非常高，因为切割技术也会影响试验结果；机械切割流程必须优先热切割，因为后者会改变靠近切割边缘材料的显微结构；试样尺寸和形状（标准长度和宽度，平行和夹紧部分的圆角半径）会影响实验结果；炉子必须足够大来容纳变形过程中的大应变 为了克服这些困难和在应力条件下更接近真实过程的测试板材，取代单轴拉伸的一些试验已经有了提议和报道；这些中有一个是基于BF技术来进行胀形试验12-14。在这项工作中，材料通过吹塑成型试验表征：使用上述实验设备，在不同的温度和压力条件下进行恒压胀形试验。根据材料特性和设备能力，试验中，压力从0.2MPa到0.8MPa（分七步），温度从360到520（分四步）。在整个过程中，压力保持恒定直到破裂。试验中，如果与预期时间有3000s的出入则被排除在计划之外。整个试验期间，每个阶段的圆拱高度使用之前的位置传感器来测定。试样的最终高度也在试验结束后进行了测量。图2显示了试验试样，破裂前的高度也绘制在内。 图2 四种温度条件下 破裂时圆拱高度和成形压力的函数 具有研究意义的最高温度和压力为520和0.2MPa。尽管使用了惰性气体来成形，但成形试样在经过2825s后还是出现了明显氧化。较好的实验结果，就破裂圆拱高度而言，在460也有出现，尤其是在低压条件下，相比之前的条件无明显氧化。另一个试验明显说明：降低温度，成形压力对试样破裂的圆拱高度影响很小。 根据15，试验中的等效应变速率值可通过下面的公式进行计算： （1）其中，h为圆拱高度，为h相对时间的导数（潮高比），R是模腔的半径。例如，在图3中，显示了460和0.3MPa下的H-T曲线和应变速率的变化。图3 0.3MPa的恒压下，460胀形试验中顶点处圆拱高度和应变率与成形时间的关系图 该图的初始部分的特征是圆拱高度快速增加相对于应变速率的增加（高于3x103S1）;该图的第二部分显示当保持一个恒定的应变速率（约2x104S3）时，高度时间关系曲线斜率基本不变；结束部分，高度和应变速率再次增长直到破裂。这个现象也存在与其他不同温度，压力，应变速率的试验中。在试验的第二阶段，从0.3MPa到0.8MPa改变压力，保持恒定的温度，发现应变速率保持在一个几乎恒定的值上，从2x104S3升到4x104S3。 图4显示了460，从0.3MPa到0.8MPa6个不同压力水平下圆拱高度的变化情况。可以看出，当需要相同的圆拱高度时，成形时间会随压力水平的提高呈线性减少。类似的现象在其他温度也出现过。考虑恒压水平和分析温度对成形行为的影响，应考虑的因素是，在自由膨胀试验中的高度速率相比温度更加线性的增加，如图4b。通过分析H-T曲线接近线性的那部分，可以根据斜率计算出圆拱高度速率。由图4b可知，温度由360升到410会使高度速率由0.006mm/s增加到0.03mm/s，当温度由460升到520时会使高度速率由0.11mm/s升到0.57mm/s。试验中，每个计算出的高度速率被认为与应变速率是成比例的，得出如下结论，应变速率的增加随温度呈线性关系。图4 a 圆拱高度在460和六个不同压力下与成形时间的关系图 b 圆拱高度在0.8MPa和四个不同温度下与成形时间的关系图 在热成形过程中一个最重要的参数就是应变速率敏感性指数，m，它可以通过不同应变速率下的拉伸试验很容易计算出来。在气胀成形领域，Jovane和其他学者如Enikeev和Kruglov16,17提出了评估胀形试验本构参数的分析方法。例如，测量两个不同压力条件下胀形试验后的高度，应变敏感性指数可通过如下公式得到：m=lnp2p1lnt1t2 （2）其中，下标1、2分别表示第一组、第二组压力水平，p为压力值，t为需要得到与凹模圆角半径相等的圆拱高度所需的成形时间。如之前提到的，镁合金在高温下的吹塑成型受到微观结构的变化也会影响m值。因此，通过（2）式计算出的m值是一个平均值，但它可以被认为是分析压力如何影响成形性能的良好的开端参数。 m的最高值出现在最高温度（460和520），最低压力（0.2MPa-0.3MPa），最高压力（0.7MPa-0.8MPa）。确认指数的重要性，破裂的最高圆拱高度对应最大的m值，通过计算不同试验温度和相同压力条件下的m的平均值，可以看到在460，该合金表现出更大的m的平均值，如图5所示。采用高的成形温度会导致晶粒变粗变大；此外板材的氧化，成形过程中温度的降低，会带来更好的最终制件18。因此，根据试验结果和这些因素，在那些被检测的结果中，这种镁合金的最佳成形温度为460，在这个温度可以实现等效断裂伸长率和后成形材料的良好折中。图5 应变速率敏感性指数与成形温度的函数曲线6.封闭模具成形为了分析封闭模腔的填充，2k多因子实验方案应用而生。这两个因素分两个层面，压力为0.4MPa和0.8MPa，成形时间为500S和1000S。另外，为了得出在模腔填充（正比于填充在封闭模腔中板材的体积）和检测的因素中是否存在非线性，补充了一个中心点。实验方案如图6a，各自具有成形压力和时间。增加了两点是在单一的压力条件下（0.8MPa），成形时间为50S和2000S的两点也被加入。在吹塑成型之后，用数字图像相关系统采集变形的轮廓来得到板材的形状，并且很容易测量该组件的主要几何参数，来量化填充模具的板材。图6 闭模成形试验 a有一个中心点，两组成形压力水平和两组成形时间 b 在已检验的压力水平下，成形后沿方形板材方向的圆角半径和成形时间的函数曲线 为了定量填充，进行了3个几何参数的测量：（i）板材和闭模底部的接触面积，（ii）沿着中间轴线所成形的的板材的圆角半径，（iii）沿对角线的平方部分所成形的板材的圆角半径。 比较二者可以看出，后者的值要大于前者。这两个参数之间的差异随着成形时间的减少而减小：0.8MPa50S后差异为11%，2000S后掉到4%。 尽管该材料达不到超塑性成形的目的，闭模试验已经证实了其在高温条件下具有很高的延展性：在0.8MPa的恒压条件下，经过2000S，板材在不破裂的情况下达到了最小的圆角半径约为1.2mm（沿中轴方向）。尽管成形时间对于传统工业应用来说并无太高成本效益，但对获得形状复杂的材料和成形过程来说是很有启发的。所有已分析的几何参数证明，充模和温度、压力这两个因素之间为非线性关系：观测试验可以看出，0.8MPa条件下，50S到500S过程中形成的圆角半径要比500S到2000S过程的大很多（如图6b所示）。中心点的结果表示充模和成形压力之间为非线性关系：相比0.6MPa条件下获得的结果，比0.4MPa条件下的，它更接近于0.8MPa条件下所获得的结果。类似的结果也在自由胀形试验中获得，证明板材的应变速率比成形压力会更加线性的增加。 众所周知，在恒压条件下，当板材接触模腔底部时，坯料的平均应变率会突然下降。常见的SPF应用中，当在最佳压力周期时，板材模腔底部接触后压力会越来越大，来保持接近目标值的应变率19。在恒压测试中，板材迅速接触模腔底部，而0.8MPa条件下经过50S后，板材已经接触了模腔底部，但需要更多的时间来校准和接触模壁（如图6b）。在这些情况下，使用高压条件，板材的应变率在接触后还是会变得很低。7.结论 高温条件下商用AZ31镁合金的成形行为在胀形和闭模试验中得到了分析。这些试验的结果得出： 为了具有超塑性行为，即使对材料不进行前处理，它也会和原来一样在断裂钱表现出大的等效伸长率； 最大伸长率出现在最高的温度和最低的压力下：在已进行试验的众多温度水平下，460可以实现断裂伸长率、应变速率敏感性指数和材料后成形条件的良好折衷； 降低成形温度，压力对断裂圆拱高度的影响也会减小；在恒温条件下，把应变率作为压力的函数或者在恒压条件下，把应变率作为温度的函数都可以得出很明显的线性关系； 在闭模成形中，材料在高温下可以达到非常小的圆角半径，表现出很高的延展性； 在检验温度和压力时，充模和成形压力有很好的线性关系，与成形时间几乎不存在线性关系。为了更好的了解镁合金在高温下吹塑成型的影响因素，还需进一步的试验研究。由于微观结构的变化和气蚀现象，后成形的特点也许更深入的分析。在加快成形周期和优化板材厚度分布的过程中，压力是可以调节的，吹塑成形被认为在生产形状复杂的薄壁镁合金组件中有很高的竞争力。8.鸣谢 作者感谢意大利机构”Ministero dellIstruzione, dellUniversit e della Ricerca”和 “Fondazione Cassa di Risparmio di Puglia”对该研究活动的投资和支持。 外文文献的原稿Blow forming of AZ31 magnesium alloys at elevated temperaturesDonato Sorgente & Leonardo Daniele Scintilla &Gianfranco Palumbo & Luigi TricaricoReceived: 29 April 2009 / Accepted: 15 June 2009 / Published online: 25 June 2009# Springer/ESAFORM 2009Abstract In this work, the forming behaviour of a commercial sheet of AZ31B magnesium alloy at elevated temperatures is investigated and reported. The experimental activity is performed in two phases. The first phase consists in free bulging test and the second one in analysing the ability of the sheet in filling a closed die. Different pressure and temperature levels are applied. In free bulging tests, the specimen dome height is used as characterizing parameter; in the same test, the strain rate sensitivity index is calculated using an analytical approach. Thus, appropriate forming parameters, such as temperature and pressure, are individuated and used for subsequent forming tests. In thesecond phase, forming tests in closed die with a prismatic shape cavity are performed. The influence of relevant process parameters concerning forming results in terms of cavity filling, fillet radii on the final specimen profile are analysed. Closed die forming tests put in evidence how theexamined commercial magnesium sheet can successfully be formed in complicated geometries if process parameters are adequately chosen. Keywords Blow forming . Material characterization .Magnesium alloys . AZ31IntroductionMagnesium (Mg) alloys are receiving increasing interest from industry manufacturers principally because of their low specific weight: among structural materials, Mg alloys have the lowest density and offer the highest potential for saving weight, especially in areas where moving components are in use. In these applications, the increasing demand for lightweight alloys, in particular for Mg alloys and the inability of conventional forming techniques to effectively form these alloys make Superplastic Forming (SPF) an attractive forming technique. In fact, lightweight components with extremely complex shapes can be manufactured by SPF from a single sheet of superplastic material. The application of the Blow Forming (BF) process is particularly interesting and innovative considering light metallic alloys such as aluminium, titanium and magnesium ones, some of which are hard to form using conventional conditions. The BF process consists in the application of aforming gas (e.g. air, argon) pressure on the blank that is forced in a die cavity. In comparison with fluid based forming operations, in the area of forming at elevated temperatures, gas offers the chance to provide higher temperatures due to its high temperature resistance in contrast to most fluids 1. The gas replaces completely the driven punch of conventional stamping processes, andallows deforming different kinds of materials with the highest level of detail. In the past, the concept of forming by blowing was applied in the traditional glassblowing, whose fundamental principle is based on forming the material at a temperature greater than the softening point.Currently, the basic principle of BF is widely used in the manufacture of plastics, for example in Blow Moulding processes. In sheet metal forming, potentialities of this process compared with conventional forming techniques are significant. It gives several advantages: (i) forming components with large and complex shapes, in a single operation with a high level of details; (ii) their manufacturing in nearly netshape, drastically reducing subsequent costly and time consuming assembly operations; (iii) the absence of male tools costs; (iv) better dimensional accuracy of finished products; (v) low springback effects on the formed part. However, SPF with BF for metals has not a large scale application in the industry, owing to the high cost of the process and raw materials, which made this type of process globally less competitive compared with other conventional technologies. In order to overcome these limits, high strain rate superplasticity (HSRSP) and some techniques as Quick Plastic Forming (QPF) have been developed and are continuously improved for achieving high volumes production requests. The successful implementation of QPF technology requires a shift away from the low-volumeassumptions typically connected with prior applications of BF processes to aerospace or niche automotive products. On the other hand, material preparation is much more restrictive: controlled microstructure with very small mean grain size are generally required 2, 3. In this work, the forming behaviour of a commercial Mg sheet has been analyzed at elevated temperatures by means of the BF technique. The used approach consists in a first phase of characterization by bulging tests and in a second part of process analysis by closed die forming tests. The main objective is to analyze the potentialities of the Mg alloy combined with the BF technique in industrial manufacturing processes. These alloys have already demonstrated to have a superplastic behaviour at elevated temperatures in different conditions 47. The ultimate goal is to look at this forming technique towards its commercially exploiting, once significant results in the optimization of process parameters and, above all, in the cycle time reduction could be achieved.Experimental setupBoth the material characterization and the closed die forming tests have been performed on a laboratory scale equipment embedded in the cylindrical split furnace of an INSTRON universal testing machine. The equipment consists in: (i) a blank-holder, (ii) a female die with different cavity shapes for generating on the blank different forming conditions, (iii) a pneumatic circuit for gas supply with an Argon cylinder, proportional electronic valves, steel tubes in proximity of the forming chamber and flexible polyurethane tubes in colder zones, (iv) an electric furnace with its electronic controller for upper, central and lower zones which can be set with three different temperatures for compensating thermal dispersion, (v) thermocouples to monitor thermal condition on the sheet and on the tools, (vi) a transducer for measuring, during bulging test, the dome height on the specimen and (vii) a PC with a data acquisition I/O device by which pressure, temperature,blank holder force can be monitored and managed. For material characterization, bulge tests are performed with a cylindrical die cavity (diameter 45 mm) in which the sheet can freely expand; the dome height of the specimen is monitored during the whole test by the digital acquisition of a position transducer signal. Further details on the equipment can be found in 8.In closed die forming tests, a die with a 14.5 mm deep prismatic cavity has been used. The cavity has a squared section with a side length of 40 mm and a fillet radius between sides of 5 mm. A schematic representation of the equipment is shown in Fig. 1 Fig. 1 Experimental setup for closed die forming testMaterial characterizationCommercial AZ31B Mg Sheets have been tested in the asreceived conditions. No mechanical or thermal treatment has been carried out on the material; sheet has been purchased in the annealed conditions with an average grain size of 153 m and a thickness of 0.75 mm. In superplastic material characterization, usually tensile tests at different temperatures and strain rates are performed in order to get optimal conditions in which material has the best performances with the highest elongation to failure. This can be done by measuring the elongation to failure instandard tensile tests and the strain rate sensitivity index in jump strain rate tests 9. Some authors have demonstrated that, when grain boundary sliding (GBS) is the predominant deformation mechanism, the stress and strain condition has a marginal role in the material characterization 10. Some other authors have demonstrated also that uni-axial tensile stress and strain conditions are not effective for obtaining material parameters due to the fact that during a forming process the sheet, interacting with the die, undergoes to a stress and strain condition that is completely different.Moreover, Mg alloys have a great tendency to grain coarsening and in several cases GBS cannot be considered as the predominant deformation mechanism 11. Furthermore, testing setup and specimen geometry for uni-axial tensile tests in superplastic conditions have to be properlydesigned. Some standards exists, such as ISO 20032 and ASTM E2448, giving indications on the best test procedures and equipments. In superplastic conditions, the great advantage of tensile tests is the possibility of controlling in a sufficiently accurate way the strain rate during the test, but on the other hand it can be said that: cutting accuracy in the specimen preparation must be very high, since also the cutting technique can influence test results; mechanical cutting processes have to be preferred to thermal cutting processes that can modify the material microstructure near the cutting edge; specimen dimensions and shape (gauge length and width, fillet radius between the parallel portion and the clamp section) can affect test results furnace must be sufficiently large to accommodate the large strain that the specimen undergoes during the testIn order to overcome these problems and to test the sheet in a strain condition more similar to the real process one, several tests alternative to uni-axial tensile tests have been proposed and reported; one of most common is based on bulge tests by means of the BF technique 1214.In this work, the material has been characterized with blow forming tests: constant pressure bulge tests at different temperatures and different pressure levels have been performed using the aforementioned laboratory equipment. Tests have been performed ranging pressure from 0.2 MPato 0.8 MPa (with 7 different levels) and temperature from 360C and 520C (with 4 different levels), according to material physical properties and to the equipment capabilities. Pressure has been kept constant during the whole test until rupture occurred. Tests with an expected forming time to failure greater than 3000 s have been excluded from the experimental plan. For each test, the dome height has been acquired during the whole test using the position transducer that described before. Final height of the specimen has also been measured after the test. In Fig. 2, tested specimens are shown and their height to failure is plotted. Fig. 2 Dome height at failure as a function of the forming pressure applied on the sheet, plottedfor four different temperatures The highest value of the height is reported for 520C and 0.2 MPa. In spite of the use of an inert forming gas, the formed specimen, after a forming time of 2825 s, appears markedly oxidised. Good results, in terms of dome height at failure, can be found also at 460C, especially for low pressure levels, with a less evident grade of oxidation on the formed sheet. Another result that can be highlighted is that, reducing the temperature, the height of the specimen at which the material fails, is less influenced by the forming pressure. Value of the equivalent strain rate during the test, according to 15, can be calculated by the following expression: (1)where h is the dome height; his the derivative of h with respect to time (height rate) and R is the die cavity radius. F