钙、镧和锶复合添加对AZ91D合金显微组织及力学性能的影响

利用X射线衍射仪、光学显微镜、扫描电镜和能谱仪等研究了在AZ91D合金中复合添加钙?镧?锶对其显微组织和力学性能的影响。结果表明:在AZ91D合金中同时加入钙、镧、锶后,其显微组织相比于钙、镧或钙、锶二元添加得到组织明显细化,析出相Mg17Al12由半连续分布变为断续状;其抗拉强度得到显著提高,达到了201 MPa,比AZ91D合金的提高了28.8%。     

半固态压铸AZ91D镁合金的时效行为

系统地研究了半固态高压压铸AZ91D镁合金铸件的时效行为.研究结果表明:无论是铸态组织还是固溶态组织、半固态高压压铸都可以有效缩短AZ91D铸件的时效时间.     

漂珠/AZ91D镁合金复合材料的显微组织与力学性能

以AZ91D镁合金为基体,以不同粒径(45128μm)的漂珠为颗粒增强相,采用搅拌铸造法制备了漂珠质量分数为010%的AZ91D镁合金基复合材料,并研究了复合材料的显微组织和力学性能。结果表明:复合材料中的漂珠分布均匀,主要由α-Mg、Mg17Al12、Mg2Si、MgO等物相组成;复合材料的硬度随漂珠含量增加而增大;当漂珠的质量分数为6%、平均粒径为60μm时,复合材料的硬度最高,为82.1HBW;当漂珠的平均粒径为90μm、质量分数为6%时,复合材料的抗压强度最高,为348.3 MPa;复合材料的断裂方式是以解理断裂为主的脆性断裂,漂珠在复合材料断裂过程中发生破损。     

铈、锶和钡元素复合添加对AZ91镁合金显微组织和力学性能的影响

采用光学显微镜、X射线衍射仪?扫描电镜和能谱仪等研究了铈、锶和钡元素复合添加对AZ91镁合金显微组织和力学性能的影响。结果表明:铈、锶和钡的加入可以显著细化该合金的铸态组织,提高合金的室温力学性能;同时添加质量分数0.5%Ce,0.2%Sr和0.2%Ba时细化效果最好,合金的粒径最小,小块状的β-Mg17Al12相最多,在基体中可弥散分布;合金的抗拉强度和伸长率达到了195 MPa和1.86%,较未添加合金元素的分别提高了25.0%和24.0%。     

Al2O3-SiO2(sf)/AZ91D复合材料时效行为的研究

采用微观组织结构观察,XRD分析和宏观硬度分析等手段研究了Al2O3-SiO2短纤维增强AZ91D镁合金复合材料的时效特性,结果表明:在不同时效温度下,Al2O3-SiO2短纤维增强AZ91D镁合金复合材料具有和AZ91D合金相似的时效硬化曲线及相同的析出相β-Mg17Al12在时效硬化过程中复合材料始终保持比AZ91D合金高的硬度,而且随着Al2O3-SiO2短纤维含量的增加硬度随之增加,时效硬化峰提前.     

钙对AZ91D镁合金流动性的影响

采用螺旋模试验法研究了钙对AZ91D镁合金流动性的影响,并用XRD、EPMA和SEM等方法对合金的物相组成和显微组织进行了分析.结果表明:当在AZ91D镁合金中加入0.5%的钙时,钙会在晶界富集引起偏析,降低合金的流动性;随着钙添加量的增加,在晶界形成Al.Ca,阻碍了晶粒长大,改善了合金的流动性能;但当钙的添加量超过1.5%后,Al2Ca呈网状分布,又会使其流动性下降.     

热处理对含微量镧AZ91镁合金组织和性能的影响

用XRD、SEM、EDS和显微硬度仪等研究了固溶、时效处理对真空精炼的含0.164 8%(质量分数)镧AZ91镁合金显微组织和力学性能的影响。结果表明:加入微量镧后的AZ91镁合金在410℃×24h空冷固溶+170℃×30h空冷时效后,第二类β相大量析出,且呈不连续层片状沿晶界两侧分布;时效态含镧AZ91镁合金的抗拉强度、屈服强度、伸长率和显微硬度分别比铸态不含镧AZ91合金的提高了41.84%,65.08%,35.65%和47.62%;其原因是微量镧改变了热处理中铝原子的扩散状态,有效控制了第一、二类β-Mg17Al12相析出时的形态与分布。     

自制覆盖剂在熔炼含铈AZ91D镁合金中的使用效果

开发了镁合金用变质处理和防氧化功效合二为一的新型覆盖剂,采用热分析仪、光学显微镜、力学性能试验机、X射线衍射仪等研究了自制NRJ覆盖剂对熔炼含铈AZ91D镁合金铸态显微组织和力学性能的影响,并与传统RJ2覆盖剂进行了对比。结果表明:含铈AZ91D镁合金采用NRJ覆盖剂熔炼后,合金组织中Mg_(17)Al_(12)相得到了细化,晶内出现了Al_4C_3形核质点,促进了基体晶粒细化;合金的抗拉强度、屈服强度及伸长率分别提高了36%,32%和146%,且拉伸断口中韧窝更多、更深;防氧化性能比用传统RJ2覆盖剂的更好。     

快速凝固结合粉末冶金法制备SiC_p/AZ91复合材料的组织及性能

用快速凝固结合粉末冶金法制备了SiC颗粒增强镁合金基复合材料(SiCp/AZ91)棒材,研究了SiC颗粒含量对复合材料室温力学性能及显微组织的影响.结果表明:制备的复合材料棒材中SiC颗粒在基体中分布均匀,但仍存在局部颗粒团聚现象;随SiC颗粒含量的增加,复合材料的屈服强度、抗拉强度和断后伸长率均逐渐降低;热挤压过程中,镁、SiC和SiO2之间发生了界面反应,在界面生成Mg2Si等脆性相,影响了复合材料的界面性能.     

添加钙和钛对Mg-12Al-2Sr-0.3Mn镁合金组织与性能的影响

研究了分别添加质量分数均为0.3%的钙、钛以及复合添加钙和钛对Mg-12Al-2Sr-0.3Mn镁合金显微组织和力学性能的影响。结果表明:添加钛提高了该镁合金的塑性和强度,然而Mg17Al12相聚集析出形成粗大的第二相组织;添加钙后提高了该镁合金的塑性,但沿晶界大量析出了连续网状Mg17Al12相,导致其强度略有下降;复合添加钛和钙既增加了共晶相数量又细化了共晶相组织,使得该镁合金铸态组织更加细小均匀,从而显著提高了其强度和韧性。     

压铸镁合金AZ91D摩擦磨损性能的研究

采用MM-200型磨损试验机，研究了干滑动摩擦条件下载荷和磨损时间对液态压铸成形镁合金AZ91D摩擦磨损性能的影响，借助扫描电镜探讨了材料的磨损机理。试验结果表明：当滑动速率为0．618m／s、载荷为20～250N时，液态压铸镁合金的磨损速率和摩擦因数均随着载荷的增大而增大，当载荷增大到250N之后，试样的磨损质量反而减小；随着磨损时间的增加，压铸镁合金的磨损质量损失呈线性比例增大，其摩擦因数在0．220～0．235范围内波动；T4和T6热处理对高载荷下镁合金材料的耐磨性能有一定的影响；随着载荷的增大，各种状态下镁合金材料的磨损机制均发生了由氧化磨损、剥层磨损、粘着磨损到熔化磨损的转变。     

Effect of heat treatment and number of passes on the microstructure and mechanical properties of friction stir processed AZ91C magnesium alloy

In this paper, the effect of heat treatment and number of passes on microstructure and mechanical properties of friction stir processed AZ91C magnesium alloy samples were investigated. From six samples of as-cast AZ91C magnesium alloy, three plates were pre-heated at temperature of 375°C for 3 hours, and then were treated at temperature of 415°C for 18 hours and finally were cooled down in air. Three plates were relinquished without heat treatment. 8 mm thick as-cast AZ91C magnesium alloy plates were friction stir processed at constant traverse speed of 40 mm/min and tool rotation speed of 1250 rpm. After process, microstructural characterization of samples was analyzed using optical microscopy and tensile and Vickers hardness tests were performed. It was found that heat treated samples had finer grains, higher hardness, improved tensile strength and elongation relative to non-heat treated ones. As the number of passes increased, higher UTS and TE were achieved due to finer grains and more dissolution of β phase (Mg₁₇Al₁₂). The micro-hardness characteristics and tensile improvement of the friction stir processed samples depend significantly on grain size, removal of voids and porosities and dissolution of β phase in the stir zone.

     

RETRACTED ARTICLE: Wear Mechanism for In Situ TiC Particle Reinforced AZ91 Magnesium Matrix Composites

TiC reinforced AZ91 magnesium matrix composites have been fabricated by a melt in situ reaction spray deposition. The microstructures of spray-deposited alloys were studied by using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The dry sliding wear behavior of the alloys was investigated by using a pin-on-disc machine under five loads, namely 10, 20, 30, 40, and 50 N. The composites had much better wear-resistance than the matrix alloy. The wear behavior of the composites was dependent on the TiC content in the microstructure and the applied load. The improvement in the wear resistance of the composites became more prominent at larger normal load. At a lower load (10 N), with increasing TiC content, the wear rate of the composite was decreased, and the dominant wear mechanism was an oxidative mechanism. At a higher loads (50 N), a spray-deposited AZ91/TiC composites exhibited superior wear resistance to the AZ91 magnesium alloy, and the dominant wear mechanism was delamination.     

镁合金表面再制造AlCoTi非晶涂层组织及力学性能研究

采用高速电弧喷涂技术在AZ91镁合金表面制备了高非晶含量AlCoTi涂层,研究了涂层显微组织、力学性能、摩擦磨损及电化学腐蚀性能。结果表明,涂层呈典型的层状结构,其结构紧凑,与镁合金基体结合良好,孔隙率约为1.63%。涂层的组织主要由非晶相、纳米结构的α-Al和Al3Ti相组成。相比于AZ91镁合金,AlCoTi非晶涂层具有更高的显微硬度和耐磨性能：涂层的显微硬度约为511.3Hv0.1,远高于AZ91镁合金(62Hv0.1);在相同的磨损条件下,非晶涂层相对耐磨性约为晶体结构AZ91镁合金的3.9倍,其主要磨损机制为脆性剥落。在0.6 mol/L NaCl溶液中,非晶涂层自腐蚀电位、自腐蚀电流密度和电荷转移电阻分别为-0.696V、0.741 8μA/cm²和33 660?·cm²,明显优于AZ91镁合金的-1.392V、769.3μA/cm²和1 914?·cm²。通过对镁合金表面不同防护涂层的电化学腐蚀性能和显微硬度比较分析,本研究为镁合金提供一种低成本、高性能的涂层材料及再制造关键技术。     

钇元素及固溶处理对AZ31镁合金组织和性能的影响

通过力学性能检测、SEM和XRD分析,研究了钇元素及固溶处理对AZ31镁合金组织和性能的影响,并分析了其断裂方式。结果表明:稀土钇元素能够细化铸态α-Mg基体组织,对镁合金具有较好的细晶强化作用;钇元素和铝元素形成的Al2Y化合物,在细化晶粒的同时均匀分布于晶界处,可强化晶界,提高合金的力学性能;钇元素质量分数为1.0%时,合金的力学性能最佳;进行440℃×10h的固溶处理能使加入0.5%(质量分数)钇元素的合金组织最为均匀;加入钇元素后,合金以韧性断裂和准解理断裂相结合的方式断裂。     

AZ31B镁合金表面激光合金化Al-SiC涂层制备及其性能研究

针对镁合金表面耐磨性差,采用预置粉末法对AZ31B表面进行激光合金化Al-SiC粉末实验。使用光学显微镜和扫描电子显微镜(SEM)、能谱分析仪(EDS)、摩擦磨损试验机、显微硬度计对合金化涂层的微结构、相组成及性能进行了分析研究。结果表明,强化层与基体呈冶金结合、组织均匀致密;合金化层主要由Mg17Al12、SiC、Mg2Si、Al4C5、Al2O3等相组成。涂层的显微硬度、耐磨损性能都明显高于基体。     

Sliding wear-induced microstructure evolution of nanocrystalline and coarse-grained AZ91D Mg alloy

Wear behavior of nanocrystalline (NC) AZ91D Mg alloy generated by surface mechanical attrition treatment and the corresponding coarse-grained (CG) samples subjected to dry sliding wear at different sliding velocities were investigated. The subsurface microstructure evolution of these two samples was analyzed by cross-sectional transmission electron microscope. The microstructure of NC layer was almost unchanged while grain refinement into nanometer scale was identified for CG sample at high velocity, which contributed to the wear behavior of both NC and CG samples.     

Fretting wear behavior of AZ91D and AM60B magnesium alloys

The fretting wear behavior of the AZ91D and AM60B magnesium alloys are investigated using a reciprocating fretting wear machine under dry conditions with different numbers of cycles, different normal loads, slip amplitudes and frequencies. The worn surfaces and wear debris were examined using scanning electron microscopy and optical microscopy in order to understand the predominant wear mechanisms of two magnesium alloys. The results indicate that the AZ91D alloy displays a lower friction coefficient and lower wear quantity than the AM60B alloy. The AZ91D shows a higher capability than AM60B in resisting crack nucleation and propagation. Both AZ91D and AM60B show similar friction and wear characteristics. The wear quantity increases with increasing normal load, but decreases with increasing frequency. The friction coefficient also decreases as the normal load is increased. Fretting frequency had little effect on the friction coefficient. In a long term, the fatigue wear and abrasive wear were the predominant wear mechanisms for AM60B and delamination wear, adhesive wear and abrasive wear for AZ91D.