Wire electrical discharge machining characteristics of AA6061/cenosphere as-cast aluminum matrix composites

Machining of metal matrix composites (MMCs) reinforced with low-density waste byproduct particulates using nonconventional processes is relatively new in the field of material science. However, more attention has been paid for investigations on nontraditional machining of such MMCs currently as the conventional machining may generate additional complexity. This study investigates the wire electro-discharge machining behavior of compo-casted cenosphere-reinforced AA6061 alloys. Cu₆₀Zn₄₀-coated copper wire was used as electrode material. The investigation demonstrates that melting and vaporization are the dominant machining mechanisms. The weight fraction of cenosphere was observed to be the most substantial process variables affecting the cutting rate, on-time, and the wire speed of tool were the next in the order of importance. The presence of nonconductive cenosphere particles along with thermal degradation of the aluminum matrix composites leads to degrading processed machined surface quality. The issues related to wire breakage and poor quality of the machined surface, surface finish, and dimensional accuracy are described in detail.     

纤维对短切碳纤维/AZ91D复合材料热变形行为和加工性能的影响纤维对短切碳纤维/AZ91D复合材料热变形行为和加工性能的影响

采用等温压缩试验研究了不同碳纤维体积分数的镁基复合材料（CFs/AZ91D）和镁合金（AZ91D）在变形温度310~430℃、应变速率10-3~10-1 s-1范围内的塑性变形行为。根据实验结果建立了CFs/AZ91D和AZ91D的热加工图,分析了纤维对CFs/AZ91D塑性加工性能与变形机制的影响。结果表明:相比ZA91D,纤维在提高复合材料流动应力的同时促进了基体动态再结晶和应变软化,但纤维体积分数对流动应力与应变软化程度影响较小,CFs/AZ91D热变形时表现出比ZA91D更高的应变速率敏感指数和变形激活能;ZA91D热加工图不存在变形失稳区且其高温低速率区变形时的能量耗散效率大于30%,CFs/AZ91D高温低应变速率区变形时的能量耗散效率大于50%,此时纤维激励了基体合金动态再结晶而使复合材料表现出极高的能量耗散效率,但在低温高应变速率变形时,基体合金与纤维之间的界面开裂极易导致CFs/AZ91D出现塑性流变失稳行为。      

LiMn2O4/活性炭复合材料的电化学性能研究

制备了不同比例的活性炭复合LiMn2O4电极材料,研究其在1mol/L Li2SO4溶液中的电化学性能.循环伏安结果表明复合后电极材料的电容包含活性炭的双电层电容和LiMn2O4电化学反应的法拉第电容,复合后响应电流在0～0.6V范围内有所增加,且含80%活性炭时响应电流达到最大;恒流充放电结果表明含80%活性炭时的放电曲线也基本呈直线,表现出较好的电容特性,仅复合了20%的LiMn2O4,其容量却增加了25%;交流阻抗结果表明含80%活性炭的复合电极的溶液欧姆电阻仅为0.1Ω,呈现出更理想的电容行为.     

Influence of additive materials on the roughness of AISI D2 steel in electrical discharge machining (EDM) environment

The quality of the machined surface resulted from the electrical discharge machining (EDM) environment is not efficient according to the previous studies. One of the significant problems is the impedance of dielectric fluid, where it is contributing to focusing the plasma channel in a limited area. Hence, this behavior leads to appearing deep craters on the machined zone. The researchers have attempted to enhance the average of surface roughness by employing powder particles or surfactant as the additive materials in the dielectric fluid. Unfortunately, these studies did not present a comparison between these additive materials in this environment. Therefore, the present study aims to compare the performance of the average of surface roughness (R_a) for AISI D2 steel by utilizing Nano chromium powder (NCP) and Span-20. The present work has proved that the behavior of the average of surface roughness for this steel is dropping at the maximum level of Nano chromium powder concentration and pulse duration as compared to the behavior with the Span-20. Moreover, the best roughness was produced by this steel with Nano chromium powder at 2 g/L and 20 μs for this powder and the pulse duration.     

Al-5Cu/B4Cp composites: The combined effect of artificially aging (T6) and particle volume fractions on the corrosion behaviour

In this study, the Al–5Cu matrix composites reinforced with different boron carbide (B₄C) particle volume fractions have been successfully produced by the hot-pressing method. Then, the artificially aging (T6) was applied to the composites for increasing their mechanical properties. The combined effect of the T6 heat treating and the B₄C particle volume fraction on the corrosion behaviour of the composites were investigated by potentiodynamic scanning (PDS) technique under aerated and deaerated 3.5% NaCl marine environments. The effect of the T6 treating on the hardness and corrosion susceptibilities of the composites were also evaluated microstructurally to contribute to their industrial use and production processes. The microstructural characterization of the composites was carried out by using a scanning electron microscope (SEM) with an attached energy dispersive spectrum (EDS) and X-ray diffraction (XRD). It was found that the corrosion susceptibilities of the composite have been interestingly decreased with increasing the B₄C particle volume fraction in the matrix while the T6 treatment enhances the pitting susceptibility of the composites. The reason of the behaviour has been discussed in details the text.