Sr对AZ91D镁合金枝晶生长和相析出的影响

加入微量Sr(0.01%-0.1%,质量分数)可明显细化AZ91D镁合金晶粒,随Sr含量增加,初生相α-Mg尺寸逐渐减小,而二次枝晶间距变化不大,同时β-Mg17Al12析出相增多.Sr添加量为0.1%时,针状或块状Al4Sr相依附在枝晶间的β-Mg17Al12相上析出.Sr在AZ91D合金凝固固-液界面前沿富集,并且优先在曲率较大的枝晶端面富集,从而抑制晶粒长大,细化了合金中初生相α-Mg;同时,Sr在枝晶的尖端富集降低了初生相α-Mg的尖端生长优势,改变了初生相形貌.     

Influence of Heat Treatment on Damping Behaviour of the Magnesium Wrought Alloy AZ61

The effect of isochronal heat treatments for 1h on variation of damping, hardness and microstructural change of the magnesium wrought alloy AZ61 was investigated. Damping and hardness behaviour could be attributed to the evolution of precipitation process. The influence of precipitation on damping behaviour was explained in the framework of the dislocation string model of Granato and Lücke.     

Influence of Cold Rolling Reduction on Microstructure and Mechanical Properties of TWIP Steel

The influence of cold rolling reduction on microstructure and mechanical properties of the TWIP (ttwinning induced plasticity) steel was investigated. The results indicated that the steel had better comprehensive mechanical properties when cold rolling reduction was about 65.0% and the annealing temperature was 1000℃. The tensile strength of the steel is about 640MPa and the yield strength is higher than 255MPa, while the elongation is above 82%. The microstructure is composed of austenitic matrix and annealing twins at room temperature, at the same time, a significant amount of annealing twins and stacking faults are observed by transmission electron microscopy (TEM). Mechanical twins play a dominant role during deformation, and result in excellent mechanical properties.     

Study on Design Techniques of a Long Life Hot Forging Die with Multi-Materials

A new design technique for the long life hot forging die has been proposed. By finite element analysis, the reason for the failure of hot forging die was analyzed and it was concluded that thermal stress is the main reason for the failure of hot forging die. Based on this conclusion, the whole hot forging die was divided into the substrate part and the heat-resistant part according to the thermal stress distribution. Moreover, the heat-resistant part was further subdivided into more zones and the material of each zone was reasonably selected to ensure that the hot forging die can work in an elastic state. When compared with the existing techniques, this design can greatly increase the service life because the use of multi-materials can alleviate the thermal stress in hot forging die.     

铝稀土合金(Al-Nd)高能微弧火花合金化的研究

用高能微弧火花合金化设备将铝稀土(Al-Nd)电极合金熔化到AZ31镁合金上以提高其耐蚀性,用极化曲线测试和浸泡试验表征合金的耐蚀性,用金相显微镜和扫描电镜观察合金化层的显微结构,用X射线衍射进行物相分析.结果表明,使用高能微弧火花Al-Nd合金化后,由于晶粒细化、快速凝固和合金化层中富含Al和Nd,可显著提高AZ31镁合金的耐蚀性.     

时效处理对AZ80镁合金冲击韧度的影响

采用冲击试验和断口形貌分析对经不同温度时效处理后的AZ80镁合金冲击性能进行了分析.结果表明,AZ80镁合金的冲击韧性随时效温度的上升呈下降趋势,当温度超过140 ℃时,合金冲击韧度迅速下降.网状组织是AZ80镁合金力学性能降低的主要原因.     

热扩散对镁合金锌铝涂层界面组织和性能的影响

选用具有较低熔点的锌作过渡层,采用热喷涂工艺在AZ91D镁合金表面制备了锌铝涂层,并分析热扩散对锌铝涂层界面组织和性能的影响.研究表明:经热扩散处理后,涂层与基体界面处形成扩散熔合区,扩散熔合区由Mg-Zn-Al金属间化合物及其固溶体组成;由于扩散熔合区的形成,使涂层的显微硬度和耐磨性能均显著提高.     

Mg-Gd-Y-Mn耐热镁合金的压缩变形行为研究

采用Gleeble-1500热模拟机对Mg-Gd-Y-Mn稀土镁合金在温度为300～500℃、应变速率为0.001～1.0s-1、最大变形程度为60%的条件下,进行恒应变速率高温压缩模拟实验研究.分析了实验合金高温变形时流变应力与应变速率及变形温度之间的关系以及组织变化,计算了表观激活能及相应的应力指数,为选择这种合金的热变形加工条件提供了实验依据.结果表明:合金的稳态流变应力随应变速率的增大而增大,在恒应变速率条件下,合金的真应力水平随温度的升高而降低;在给定的变形条件下,计算得出的表观激活能和应力指数分别为200kJ·mol-1和5.1.根据实验分析,合金的热加工宜在400～500℃温度范围内进行.     

中间退火对镁合金板材组织和性能的影响

研究AZ31B镁合金轧制道次间不同退火温度和时间对板材微观组织和力学性能的影响,分析了拉伸试样断口形貌.实验结果表明,退火处理后镁合金板材由轧制纤维组织转变为均匀等轴的再结晶组织,退火再结晶的起始温度为200℃;退火后的力学性能得到一定程度的恢复,硬度、屈服强度最大降幅分别为25.4%和37.1%,伸长率最大增幅达31.3%,拉伸断口由解理和韧窝混合断口转变为典型韧性断口.实验得到镁合金中间退火的较佳工艺为:退火温度300～320℃,退火时间60～120 min.     

退火处理对等径角轧制AZ31镁合金板材组织与性能的影响

通过显微组织分析和力学性能测试对退火处理后等径角轧制AZ31镁合金板材进行了研究,在试验条件下,退火处理后板材中原有的非基面晶粒取向未发生明显改变;随着退火时间的延长,退火温度的升高,晶粒逐渐趋于均匀、等轴化并发生长大,孪晶消失,抗拉强度和屈服强度逐渐降低,断裂伸长率明显提高,各向异性减弱.这表明,孪晶的存在及晶粒粗化导致板材的塑性降低,而非基面晶粒取向和均匀等轴化的晶粒组织则有利于其塑性的提高,明显的屈服现象、低的屈服强度和大的应变硬化现象可归因于板材内(0002)基面晶粒取向的减弱.