漂珠/AZ91D复合材料微观组织与性能的研究

采用搅拌铸造法,向镁合金熔体中添加漂珠,制备了漂珠/AZ91D复合材料,研究了该复合材料微观组织的均匀性、相组成、力学性能和阻尼性能。结果表明,漂珠在基体中分布均匀,无偏聚现象。在复合材料制备过程中,漂珠与镁合金熔体发生反应并被填充,使得复合材料中有Mg₂Si和MgO相生成。与基体合金相比,复合材料的力学性能和阻尼性能均得到明显提高。复合材料的断裂是以解理断裂为主的脆性断裂,在断裂过程中漂珠壁被撕裂。复合材料的阻尼机制主要是位错阻尼和界面阻尼。     

The high strain rate compressive response of Mg-Al alloy/fly Ash cenosphere composites

The strain rate dependence of mechanical properties of AZ91D alloy composites filled with 5 wt.% hollow fly ash cenosphere is examined in the strain rate range of 630–1,203 s⁻¹ using a split-Hopkinson pressure bar system. In addition, a test scheme is designed to study the intermediate strain rate response of the material. Addition of fly ash caused grain refinement and finer precipitates in the matrix alloy. Compared to the matrix alloy, the energy absorption is higher in AZ91D/fly ash cenosphere composites at comparable strain rates. In addition, the yield strength is found to be about 19–41% higher in the composites containing fly ash cenospheres.     

Microstructure of fly ash cenosphere/AZ91D composite during solution treatment at 380-420℃

The fly ash cenosphere/AZ91D (FAC/AZ91D) composites containing 5 wt.% and 100 μm in size of fly-ash cenosphere particles were fabricated by means of the compcasting method.The microstructures of the as-cast samples and the effect of the solution treatment at 380℃,400℃,and 420℃ for 16 h on the microstructures of the samples were investigated by using of OM,SEM,XRD and EDS.The results showed that the cenospheres distributed homogeneously in the Mg alloy,and were almost filled with Mg alloy.The main interfacial phase between the cenospheres and AZ91D Mg alloy was identified as MgAl2O4 according to XRD,EDS and thermodynamic analysis.Mg2Si particles tended to be spheroidized via the solution treatment and the β phase (Mg17Al12) dissolved completely at 400℃.     

Dry Sliding Wear Behavior of Fly Ash Cenosphere/AZ91D Mg Alloy Composites

Fly ash cenosphere/AZ91D Mg alloy (FAC/AZ91D) composites were prepared using stir casting method. The effects of the applied load, the wearing time, and the diameter and the content of fly ash cenosphere on the wear behavior of the composites were investigated under dry sliding condition. The results showed the wear resistance of FAC/AZ91D composites is generally better than that of AZ91D Mg alloy. The mass fraction and diameter of FAC have important effects on the wear resistance of the composites, and the wear resistance of the composites is excellent when the mass fraction and diameter of FAC are moderate. When the mass fraction and diameter of FAC are more than the critical values, the wear resistance of the composites lowers again. The wear resistance of the composites decreases with the increase in the applied load. The relationship between the worn mass loss and the applied load is nonlinear. When the applied load is smaller, the worn mass loss of the composites increases rapidly with the increase of the applied load. These research results show that the composites have broad application prospects under dry sliding wear condition, and they can provide guidance for the selection of the raw materials, the structure design, and the application conditions of the composites.     

Microstructure characterization on the formation of in situ Mg2Si and MgO reinforcements in AZ91D/Flyash composites

5 wt.% and 100 μm in size of fly ash cenosphere particles were incorporated in AZ91D Mg alloy to fabricate in situ Mg₂Si and MgO reinforced AZ91D/Flyash composites by means of compocasting method. The in situ Mg₂Si and MgO were identified using X-ray diffraction (XRD), energy dispersive spectrometer (EDS), and thermodynamic analysis. The results show that the cenosphere particles distributed homogeneously in the matrix alloy. Moreover, most of the cenosphere particles were filled with the matrix alloy. The preliminary discussion was carried out on the growth mechanism of the in situ Mg₂Si.     

Microstructures and compressive properties of AZ91D/fly-ash cenospheres composites

Novel AZ91D Mg alloy/fly-ash cenospheres(AZ91D/FACs)composites were fabricated by melt stir technique.Fly-ash cenosphere particles with 4%,6%,8%,10%in mass fraction and 100μm in size were used.Hardness and compressive strength of the composites were measured.The effects of mass fraction of cenospheres on the microstructure and compressive properties were characterized.The results show that the cenospheres are uniformly distributed in the matrix and there is no sign of cenosphere cluster or residual pore.The densities of the composites are 1.85-1.92 g/cm 3 .By comparing with matrix,the compressive yield strength of the composites is improved,and the cenospheres is filled with Mg matrix alloy.SEM,XRD and EDX results of the composites show clear evidence of reaction product at cenosphere/matrix interface.On the basis of XRD and EDX,composition, structure and thermodynamic analysis,the main interfacial phase between the cenosphere and AZ91D Mg alloy was identified to be MgAl2O4.     

Al2O3sf/AZ91D-Y镁基复合材料二次重熔及等温压缩研究

为了推动半固态加工在镁基复合材料成形中的应用,采用液态浸渗法制备出体积分数为10%的Al2O3sf/AZ91D-Y镁基复合材料,并采用等径道角挤压对镁基复合材料进行了形变诱导。再对镁基复合材料进行了二次重熔,并采用等温压缩实验对镁基复合材料在半固态下的力学性能进行了研究。研究表明：在550℃和560℃时延长保温时间有利于组织的球化,在560℃比550℃时,更加能促进晶粒的结晶球化;在相同的应变速率下,压缩变形时的峰值应力随着加热温度升高而降低;在相同的加热温度下,应变速率越大,峰值应力越大。     

High strain rate compressive characterization of aluminum alloy/fly ash cenosphere composites

The strain rate dependence of compressive response is determined for aluminum alloy/hollow fly ash cenosphere composites. A4032 alloy is used as the matrix material. Quasi-static and high strain rate compression tests are conducted on the matrix alloy and the composite. A split-Hopkinson pressure bar is used for high strain rate testing. While the matrix alloy does not show any appreciable strain rate sensitivity, the composite shows higher strength at higher strain rates. The energy absorption capability of A4032/fly ash cenosphere composites is found to be higher at higher strain rates.     

Sr对AZ91D镁合金半固态等温热处理后的组织的影响

通过对等温热处理温度和时间等工艺参数的控制，研究了变质剂Sr对AZ91D镁合金半固态等温热处理后组织的影响。结果表明，随着等温时间的延长，未变质处理的合金组织将由树枝晶变成近球状组织，而经Sr变质处理的合金组织将由树枝晶变成细小的球状组织，都将逐渐合并长大。等温热处理过程中，树枝晶经历了熔断、粒状化、球化和粗化。     

热处理对SiCp/AZ61镁基纳米复合材料阻尼性能的影响

实验采用自行设计的高能超声装置制备SiCp/AZ61镁基纳米复合材料(MMNCS),并对制备的复合材料进行了阻尼性能测试。研究时效处理(T5)、固溶处理(T4)及固溶后时效处理(T6)3种不同热处理工艺,对挤压态n-SiCp/AZ61 MMNCs阻尼性能的影响。研究表明,不同的热处理工艺对n-SiCP/AZ61复合材料阻尼性能的影响较显著。与挤压态的n-SiCP/AZ61复合材料相比,T4态和T6态与应变相关部分的阻尼得到了较大幅度提升。在T6态时,随着时效时间的延长,复合材料的阻尼性能下降。不同热处理工艺对AZ61镁合金阻尼性能的影响规律,室温可通过G-L理论,高温时可由界面阻尼机制很好的解释。     

CNTs/AZ91D镁基纳米复合材料的热处理及其力学性能

采用高能超声分散技术和金属型重力铸造工艺制备了CNTs/AZ91D镁基纳米复合材料,并对复合材料进行了固溶T4热处理和固溶时效T6热处理。T4态1.0CNTs/AZ91D复合材料的抗拉强度、伸长率分别为285 MPa、17.3%,与铸态复合材料的抗拉强度(196MPa)和伸长率(4.1%)相比,分别提高了45%、322%。T6态的抗拉强度进一步提高到296MPa,特别是屈服强度显著提高到155MPa,伸长率有所降低,但仍有5.5%。利用OM、SEM、TEM观察1.0CNTs/AZ91D复合材料的显微组织。结果表明,碳纳米管具有细化晶粒、促进滑移和孪生、载荷转移等作用,从而能够明显提高CNTs/AZ91D复合材料的综合力学性能。     

用粉煤灰和锆英石制备β-Sialon/ZrN/ZrON 复合材料

以粉煤灰、锆英石和活性炭为原料,采用原位碳热还原氮化法成功制备β-Sialon/ZrN/ZrON 复合材料。研究配料组成和保温时间对合成过程的影响,并讨论材料的生成过程。通过XRD和SEM表征材料的相组成和显微组织。结果表明：增加试样中的碳含量以及延长保温时间均能促进β-Sialon、ZrN 和ZrON 的生成。合成β-Sialon/ZrN/ZrON复合材料的适宜工艺参数为锆英石、粉煤灰和活性炭的质量比49：100：100、合成温度1550°C、保温时间15 h。在1550°C保温15 h合成的β-Sialon 和ZrN(ZrON)的平均粒径分别约为2和1μm。β-Sialon/ZrN/ZrON复合材料的制备过程包括β-Sialon和ZrO2的生成过程以及 ZrO2向ZrN和ZrON的转化过程。     

ZL401合金的阻尼行为研究

对铸态ZL401合金进行了低温人工时效处理，利用低频内耗测试技术研究了合金的阻尼性能及实模量与应变振幅、频率和温度的关系，并与铸态合金进行了对比。发现合金阻尼与应变振幅及应变频率相关，随温度的提高而增大，且在低温和高温时合金阻尼与频率的关系出现了相反的变化。ZL401合金振动过程中实模量的亏损随频率的降低和温度的升高而增大。认为ZL401合金的阻尼行为是界面阻尼和位错阻尼二者效应叠加的结果，室温阻尼主要归功于位错阻尼，而高温阻尼主要归功于界面阻尼。     

SiC_p/AZ91镁基复合材料的热挤压

采用搅拌铸造法制备SiC体积分数为5%、10%和15%的颗粒增强AZ91镁基复合材料（SiCp/AZ91）。复合材料经过T4处理后,于350°C以固定挤压比12：1进行热挤压。在铸态复合材料中,颗粒在晶间微观区域发生偏聚。热挤压基本上消除了这种偏聚并有效地改善颗粒分布。另外,热挤压有效地细化基体的晶粒。结果表明：热挤压明显提高复合材料的力学性能。在挤压态复合材料中,随着SiC颗粒含量的升高,基体的晶粒尺寸减小,强度和弹性模量升高,但是伸长率降低。     

SiC_P/AZ61复合材料半固态触变成形的数值模拟

采用等温热处理法制备SiCP/AZ61复合材料半固态坯料。运用所建立的高固相SiCP/AZ61复合材料本构模型,对其触变成形过程进行数值模拟,得到成形过程中的应力和应变分布,并对比了触变成形和常规成形的成形特点。结果表明,SiCP/AZ61复合材料触变成形具有变形抗力小、应力分布均匀的特点。通过对比试验结果和模拟结果可知,两者吻合较好,所获结果可指导镁基复合材料触变成形工艺实践。     

热处理对挤压态AZ61合金力学性能和阻尼性能的影响

采用拉伸实验、硬度及电阻率测试、动态机械热分析、显微组织观察等方法研究了退火及时效对挤压态AZ61合金力学性能及阻尼性能的影响。结果表明:未经均匀化处理的AZ61合金热挤压后再经过退火(573K×1h),抗拉强度几乎不变;固溶处理(693K×1h)使合金的应变无关阻尼降低,但使应变相关阻尼提高。固溶处理后的时效(453K×24h)由于有少量第二相析出,明显提高合金的屈强比,且因增加了合金基体中强钉扎点的数量使阻尼性能较固溶处理后的稍有降低。该合金室温阻尼可用G-L位错钉扎模型解释。     

AZ91D熔体中原位合成TiC颗粒及冲刷腐蚀性能

利用原位合成反应法,在不同温度(740、760和780℃)下对AZ91D镁合金熔体保温40min,制备了TiC/AZ91D镁基复合材料。借助光学显微镜和X射线衍射仪,对TiC/AZ91D镁基复合材料的组织形貌和物相进行观察和分析,并对制备的复合材料在质量分数为3.5%的NaCl溶液+石英砂条件下进行冲刷腐蚀磨损试验。结果表明,在740℃保温40min制备的复合材料主要由α-Mg、β-Mg17Al12和Al3Ti组成。保温温度分别为760℃和780℃时,AZ91D镁合金中均出现了原位合成的TiC颗粒,并且随温度升高,TiC的数量增加。此外,TiC/AZ91D镁基复合材料在3.5%的NaCl溶液+石英砂中的冲刷腐蚀磨损性能随保温温度的升高而增加。经780℃保温40min后的复合材料呈出最好的耐冲刷腐蚀磨损性能,相比于AZ91D镁合金提高了60.5%。     

Influence of heat treatment on the internal friction of 2D-C/SiC composites

The internal friction of two-dimensional C/SiC composites (2D-C/SiC) was investigated in air by means of three-point bending forced vibration, compared with the specimens after heat treatment. The result shows that the effects of PyC interface between carbon fibers and SiC matrix play an important role on the internal friction characters of 2D-C/SiC composites, which leads to some unique internal friction phenomena in 2D-C/SiC composites. After the heat treatment, the PyC interface produces damage that make internal friction increased and dynamic modulus decreased. The heat treatment makes the internal friction of 2D-C/SiC composites more insensitive to temperature and frequency, and more sensitive to amplitude.     

Thermal expansion and dimensional stability of unidirectional and orthogonal fabric M40/AZ91D composites

Unidirectional (60%, volume fraction) and orthogonal (50%, volume fraction) M40 graphite fibre reinforced AZ91D magnesium alloy matrix composites were fabricated by pressure infiltration method. The coefficients of thermal expansion (in the temperature range of 20-350 ℃) and dimensional stability (in the temperature range of 20-150 ℃) of the composites and the corresponding AZ91D magnesium alloy matrix were measured. The results show that coefficients of thermal expansion of the composites in longitudinal direction decrease with elevating temperature. The coefficients of thermal expansion (CTE) for unidirectional M40/AZ91D composites and orthogonal M40/AZ91D composites are 1.24×10-6 ℃-1 and 5.71×10-6 ℃-1 at 20 ℃, and 0.85×10-6 ℃-1 and 2.75×10-6 ℃-1 at 350 ℃, respectively, much lower than those of the AZ91D alloy matrix. Thermal cycling testing demonstrates that the thermal stress plays an important role on residual deformation. Thus, a better dimensional stability is obtained for the AZ91D magnesium alloy matrix composites. More extreme strain hysteresis and residual plastic deformation are observed in orthogonally fabric M40 reinforced AZ91D composite, but its net residual strain after each cycle is similar to that of the unidirectional M40/AZ91D composite.     

AZ91D镁合金屑的固相再生(英文)

利用固相再生技术回收利用AZ91D镁合金屑,具体工艺为先冷压再热挤。结果表明:制备的AZ91D镁合金具有较好的力学性能且晶粒明显细化。在热挤出过程中发生了动态再结晶,且动态再结晶组织受到热挤温度和应变速率的影响,在300-350 °C下基面滑移和孪晶协调变形导致动态再结晶晶粒产生,形成"项链"组织;在 350-400 °C下位错的交滑移控制动态再结晶形核;高于400 °C时位错攀移控制了整个动态再结晶过程,形成均匀的再结晶组织。随着应变速率增加AZ91D镁合金力学性能增大,改善了材料的力学性能,但应变速率过大,制备试样表面出现裂纹,影响材料的力学性能。