Microstructure and tensile properties of magnesium alloy modified by Si/Ca based refiner

Microstructure and mechanical properties of pure magnesium and AZ31 alloy with Ca/Si based refiner addition were investigated. The results indicate that addition of Ca/Si based refiners to pure magnesium and AZ31 alloy results in remarkable microstructure refinement. With proper amount of refiner addition, the grain size in as cast ingots can be one order of magnitude lower than that without refiner addition. Small amount of refiner addition to AZ31 alloy increases both ultimate strength and yield strength significantly,while the ductility of the alloy with refiner addition is similar to that without refiner addition. Addition of refiner improves the deformability of AZ31 alloy and extruded or hot rolled specimens （rods or sheets） with refiner addition exhibit higher surface quality and mechanical properties than those without refiner addition.     

Thixoforming of SiC ceramic matrix composites in pseudo-semi-solid state

1INTRODUCTIONIt has great economic profit to exploit the uti-lization of SiC ceramic material for its strength,hardness,wear resistance,corrosion resistanceand high temperature resistance,abundant re-source and low price.But the brittle charactergreatly restricts its application in the field of engi-neering structure materials.Recently a series ofceramic matrix composites with exi mious perform-ance have been developed by reinforcing the matrixmaterial with other materials.Al/SiC is a la…     

Tribological behavior of high specific strength PTFE-Al alloy composite

Solid lubricants lead to substantial weight savings relative to the use of liquid lubricant, especially in the weight-conscious aerospace industry. A new PTFE-Al alloy composite（A） containing 60% area proportion of PTFE composite was developed. Another type of common metal-plastics multilayer composite, also called DU, was selected for a comparative investigation. Friction and wear tests were carried out in an oscillating sliding tribotester in air at an oscillating frequency of 0.13 Hz and contact mean pressures from 10 to 80 MPa. The composites slid against a 38CrMoAlA steel shaft. The results show that the composite A exhibits low coefficient of dry sliding friction less than 0.1 and long wear life of 2 000 m. This is because the composite A can provide a sufficient solid lubrication during the whole tests. SEM examination of the transfer films for the composite A confirms that uniform, thin and coherent transfer films are prerequisites for low friction and good wear resistance.     

超过冷条件下Fe83B17共晶合金的凝固行为及显微组织演化

采用深过冷技术研究了块体Fe83B17共晶合金在超过冷度条件下的凝固行为．该合金的组织演化规律为：当过冷度达到理论临界超过冷度（300K）时，组织为α-Fe相和Fe2B相组成的共晶组织；当过冷度大于临界值达到386K时，组织粗化，为完全的非规则共晶，稳定相Fe2B消失，亚稳相Fe3B出现并且在室温下也不会分解；获得了460K的超过冷度以及亚稳相组织．并讨论了这些结果产生的原因．     

含钪铝合金的钎焊工艺

探讨了Al-Zn-Mg-Sc-Zr铝合金采用炉中钎焊的可行性。结果表明，通过选用合理的钎料和钎剂组合以及优化试验条件下的钎焊工艺参数，可获得焊缝表面成形良好的钎焊接头。对获得的接头进行力学性能测试，结果表明，文中试验条件下获得的钎焊接头具有相对较高的抗剪强度；金相组织观察显示，钎缝金属组织致密，未发现有气孔、夹渣和微裂纹等焊接缺陷；扫描电镜观察显示接头拉伸断口大部呈韧性断裂机制。钎缝微区成分分析表明钎料与母材之间存在明显的合金元素互扩散，钎缝与母材之间结合良好；X射线衍射相结构分析表明，接头钎缝金属中含有Al，Sc、Al，Zb等组成相，对提高接头抗翦强度具有重要作用。     

复杂结构中焊接缺陷的空间分布特征

采用X射线实时成像方法对复杂结构钛合金激光焊件进行了无损检测,并基于缺陷位置的线灰度分布曲线确定了焊件中微小缺陷的空间位置,推导出了一个计算缺陷埋藏深度的公式。针对峰值异常和斜凹形异常缺陷分别提出了一个缺陷到射线穿透焊件最薄处的投影距离自动提取算法。试验结果表明,上述算法能很好地计算出投影距离并进而确定缺陷空间分布特征。     

铸铁表面激光熔覆铁基自熔合金的组织与性能

在球墨铸铁基体上进行铁基自熔合金激光熔覆，通过改变扫描速度和送粉速度获得不同条件下的熔覆层，并对其进行显微组织观察与性能测试，从而得出工艺参数对熔覆层组织、性能的影响。     

Cu-2.8Ni-0.7Si-0.15Mg合金的时效性能

对不同变形量的Cu-Ni-Si-Mg合金进行时效处理,研究了变形量、时效温度及时效时间对合金性能的影响。结果表明,时效前的预冷变形能够促进合金在时效过程中第二相的析出,从而提高合金的显微硬度和导电率。当合金经60%的冷变形,在450℃时效1 h,能获得较高的显微硬度与导电率,分别达到242 HV0.2和35.5%IACS。同时建立了该合金在450℃下,关于时效时间的相变动力学方程和导电率方程。     

深冷处理对AZ31镁合金焊接接头组织与性能的影响

针对镁合金焊接接头的软化问题,采用不同深冷时间对AZ31镁合金MIG焊接接头进行了深冷处理,并测试与分析了不同深冷时间下焊接接头的力学性能和显微组织。结果表明,深冷处理可显著强化AZ31镁合金焊接接头,其中经过(-196℃,12 h)深冷处理后的焊接接头,硬度提高了8.3%,抗拉强度与伸长率分别提高了15.43%和10.16%;随着深冷时间的延长,焊接接头的组织进一步细化,并有第二相在基体上不断析出,且呈弥散分布。     

Grain size stability of Mg-4AI-2Si alloy prepared by reciprocating extrusion

对铸态Mg-4Al-2Si合金经4道次往复挤压后,在长时间保温条件下晶粒尺寸的稳定性进行了研究。结果表明,随保温时间延长,Mg-4Al-2Si合金晶界及晶内析出相的数量变化不大,平均品粒尺寸逐渐增大。尺寸在15μm以下的晶粒数量呈下降趋势,而尺寸超过15μm的晶粒所占比例则逐渐增多。