半固态AZ91D流变铸轧正交试验研究

在半固态AZ91D镁合金铸轧工艺试验研究中,选取机械搅拌速度、机械搅拌时间、熔体静置时间和浇铸温度作为试验因子,用正交试验法进行半固态AZ91D镁合金流变铸轧试验;用极差分析法分析了试验结果.结果表明:对半固态AZ91D镁合金组织结构的影响主次顺序为:搅拌速度、静置时间、浇注     

变形镁合金热压缩变形流变应力研究

由于镁是密排六方晶体结构,纯镁及镁合金在室温下只有很小的延展性,其成形工艺应在中高温下进行.针对AZ91D与ZK60镁合金,采用Gleeble 1500D热模拟试验机对其在不同温度和变形速率下的流变应力进行了实验研究.结果表明,AZ91D与ZK60镁合金具有不同形式的热模拟曲线,不同的流变应力规律.     

AZ91D镁合金半固态静态剪切流变特征的研究

为了研究镁合金在半固态下的流变特征，依据铸造合金的流变学原理，利用自制的模具，在电子万能试验机上对AZ91D镁合金半固态坯料进行了半固态静态剪切流变试验，分析了保温时间、原始组织等参数对流变特征的影响，建立了AZ91D镁合金半固态流变特征的H1-（N1／H2）-（N2／S）五元件机械模型．结果表明，在加载条件不变的情况下，变形速率随加载时间和保温时间的延长而增大；半固态状态下存在一个发生变形的临界剪切应力；临界剪切应力和最大剪切应力随保温时间的延长而减小．     

半固态镁合金触变成形技术

论述了镁及镁合金的特性、工艺特点，阐述了半固态镁合金触变成形的关键技术及其计算机数值模拟的最新进展，着重从非枝晶坯料的制备、二次加热重熔、半固态镁合金的触变成形及其计算机数值模拟等四个方面介绍了镁合金半固态成形技术目前的研究与应用现状，并且介绍了当今国内外利用电磁搅拌法和应变诱发熔体激活法SIMA(strain—Induced Melt Activation)制备半固态镁合金非枝晶组织转变过程的最新成果展望了半固态镁台金触变成形技术的发展前景．     

半固态镁合金压铸充型过程的数值模拟研究

在考虑半固态AZ91D镁合金充型过程的压力和速度变化特征的基础上,建立了模拟计算所需要的表观黏度数学模型。采用ProCAST软件,对半固态镁合金压铸充型过程进行模拟,预测卷气、夹杂物产生的可能性,以便优化其工艺参数和工艺方案。结果表明,与全液态镁合金充型过程相比,半固态金属充型平稳,模具寿命长,铸件质量好;改变内浇道和溢流槽的设置位置和数量,还可有效地减少铸件本身内部杂质,提高铸件质量。     

挤压态和压铸态AZ91镁合金的摩擦磨损行为

以挤压态和压铸态AZ91镁合金为对象,研究其在干摩擦条件下的摩擦磨损行为,分析两种成形工艺对AZ91镁合金摩擦磨损性能的影响,并探讨其磨损机制。研究表明:随着载荷增加,两种镁合金的摩擦因数均减小,而磨损量增加;随着转速提高,两种镁合金的摩擦因数均减小,而磨损量增大;在相同磨损条件下,挤压态AZ91镁合金的摩擦因数和磨损量均低于压铸态AZ91镁合金;挤压态AZ91镁合金和压铸态AZ91镁合金在干滑动摩擦条件下具有相同的磨损机制,50 N载荷加载下的磨损机制主要为磨粒磨损和氧化磨损,100 N载荷加载下的磨损机制主要为轻微剥层磨损、黏着磨损和氧化磨损,150 N载荷加载下的磨损机制为剥层磨损、氧化磨损和黏着磨损。     

加入钙和稀土对AZ91D镁合金起燃温度的影响

镁合金在熔炼及压铸过程中易发生氧化燃烧。在众多的阻燃方法中,以合金化阻燃方法的效果最为明显。研究了加入混合轻稀土和Ca对AZ91D镁合金起燃温度的影响,观察了镁合金的金相组织,测试了各合金试样的起燃点,并进行了总结与比较。结果表明,Ca对提高AZ91D镁合金的起燃点有显著的作用,加入量为2％时,起燃点可提高至768℃;混合轻稀土对AZ91D镁合金的起燃点的影响与钙相比,效果更加明显,稀土加入量为2％左右,起燃点达到802℃。稀土更有利于提高AZ91D镁合金的起燃温度。     

镁合金电镀镍涂层的耐蚀性能

以化学镀镍作为保护层,对AZ91D镁合金进行直流电镀镍涂层以提高其耐腐蚀性能,并对镁合金表面两个不同厚度的镀镍涂层进行了比较.采用SEM对涂层的表面形态进行了研究.在X射线下纹理明显.镍涂层硬度约560VHN,远远高于AZ91D镁合金基底的硬度(约100VHN).电化学测量结果表明,在已经研究的镁合金涂层中,镍镀层有最低的腐蚀电流密度和最高的腐蚀电位.加速腐蚀实验中AZ91D镁合金镀镍具有很高的耐腐蚀性能.     

AZ91镁合金热挤压成形工艺的研究

通过对均匀化退火后的AZ91镁合金热挤压成形工艺试验研究,分析了热挤压成形时挤压力以及组织性能的变化规律．结果表明：挤压力随挤压温度的升高、挤压比和挤压速度的减小而下降,抗拉强度随挤压温度、挤压比和挤压速度的升高而升高,同时证明了均匀化后的AZ91镁合金具有良好的挤压成形性,其制品有较好的综合力学性能,抗拉强度σ6均在310—340MPa之间,延伸率8在10％-12％之间．     

镁合金表面电镀锌的预处理工艺研究

用AZ91D镁合金制样，研究了采用碱性镀锌工艺对高纯镁合金进行电镀的预处理工艺性能。所得镀层均匀致密，外观质量良好，与基体结合牢固，可将碱性镀锌用作高纯镁合金电镀其它金属的预处理工艺。     

Microstructural formation of semi-solid AZ91D alloy stirred by electromagnetic field

With the help of an electromagnetic stirring device, alloy melt quenching and EBSD (electron back scatter diffraction)analysis technology, the microstructure of the semi-solid AZ91D magnesium alloy slurry stirred by rotational electromagnetic field under different stirring power conditions has been studied. The results show that the size of primary α-Mg phase is reduced obviously when the solidifying alloy melt is stirred by rotational electromagnetic field, moreover, the primary α-Mg grains are changed to fine rosette grains or spherical grains which are proved to belong to the different grains in three-dimension by the EBSD analysis technology. The results also show that the stirring power is an important processing parameter in the preparation of the semi-solid AZ91D magnesium alloy slurry. The larger the stirring power, the finer the primary α-Mg grains, the less the rosette primary α-Mg grains, and the more the spherical primary α-Mg grains. Theoretical analysis indicates that a stronger flow motion leads to a more even temperature field and solute field and a stronger man-made temperature fluctuation in the alloy melt so that the specially fine rosette and/or spherical primary α-Mg grains are formed in the semi-solid AZ91D magnesium alloy slurry.     

Electroless Ni-P deposition on magnesium alloy from a sulfate bath

A technology for electroless Ni-P deposition on AZ91D from a low cost plating bath containing sulfate nickel was proposed. The seal pretreatment was employed before the electroless Ni-P deposition for the sake of occluding the micro holes of the cast magnesium alloy and interdicting the bubble formation in the Ni-P coating during plating process. And pickling pretreatment can provide a better adhesion between the Ni-P deposition and AZ91D substrate. The deposition speed of the Ni-P coating is 29 μm/h. The technology is employed to AZ91D magnesium alloy automobile parts and can provide high hardness and high wear-resistant. The weight losses of Ni-P plated and heat-treated Ni-P plated magnesium alloy specimen are only about 1/6 and 1/10 that of bare magnesium alloy specimen after 10 min abrasion wear, respectively. The hardness of the electroless Ni-P plated brake pedal support brackets is 674.1 VHN and 935.7 VHN after 2 hours heat treatments at 180 C. The adhesion of Ni-P coatings on magnesium alloy substrates meets the demands of ISO Standards 2819. The technology is environment friendly and cannot cause hazard to environment because of absence of chromate in the whole process.     

钙和碳变质对AZ91D显微组织与性能的影响

镁合金的晶粒细化对于材质的金相组织和力学性能起着决定性作用．本课题通过在AZ91D中加入Ca和C2Cl6晶粒细化剂,分别研究了Ca,C对AZ91D组织以及力学性能的影响．利用熔剂保护法,制备了AZ91D标准拉伸试样,经过T4,T6处理后,采用金相显微镜（Olympus）、扫面电镜（SEM）和能谱分析仪（EDAX）对制备的试样进行了显微组织、断口形貌及成分进行了观察与分析,并测试了抗拉强度和布氏硬度．试验结果表明：经过显微组织和断口形貌观察,加入细化剂后形成Al4C3,有效的抑制了晶粒的长大,使晶粒得到细化,当Ca和C2Cl6复合应用时,使得AZ91D的晶粒细化更加明显,力学性能得到提高,抗拉强度最高达到216N／mm^2,布氏硬度值达到60HB．     

Effects of ultrasonic field on microstructures and properties of semi-solid AZ91D magnesium alloy

The microstructure distribution rule of semi-solid AZ91D alloy treated by ultrasonic was researched, and mechanical properies of specimens before and after ultrasonic treatment were investigated further.Semi-solid AZ91D melt specimens were processed by ultrasonic under different powers, and its microstructures and mechanical properties at different sampling points in specimens were obtained. The experimental results show that the microstructure of AZ91D alloy at different sampling points under the same ultrasonic power is different in grain size and shape, and there is also great difference among their microstructures at the same sampling point under different ultrasonic powers. AZ91D alloy treated by ultrasonic can obtain increment in both tensile strength and plasticity. Under same ultrasonic power, mechanical properties of specimen at different sampling points have obvious difference, and regularity for change of mechanical properties everywhere is similar to regularity for change of grain size and shape everywhere.     

Y和Ce对AZ91D镁合金显微组织和力学性能的影响

为了开发低成本、高强度、耐高温的新型镁合金,研究了微量Y、Ce对AZ91D镁合金显微组织和力学性能的影响。研究结果表明:Y和Ce复合加入AZ91D镁合金,能明显细化组织晶粒,从而改善合金在室温和高温下的力学性能。当加入0.6%Ce-0.3%Y(质量分数)时,合金晶粒细化效果较好,其室温和高温力学性能比较理想。     

压铸镁合金材料内耗值的测量与减振机理

采用自行研制的材料内耗检测仪，对AZ91D压铸镁合金材料的内耗值进行测试，并和同体积的钢、铝材料的内耗值对比。结果表明，镁合金比钢、铝等材料具有较高的内耗值，镁合金减振机理为位错钉扎材料晶界，Mg17Al12相及其它杂质、空洞是产生内耗的主要原因。