Effect of Fe on Microstructure and Properties of 8xxx Aluminum Conductor Alloys

The effect of Fe contents (0.3-0.7 wt.%) on the microstructure, electrical conductivity, mechanical and creep properties of 8xxx aluminum conductor alloys was investigated. Results revealed that the as-cast microstructure of 8xxx alloys was consisted of equiaxed α-Al grains and secondary Fe-rich intermetallics distributed in the interdendritic region. The extruded microstructure showed partially recrystallized structure for 0.3% Fe alloy but only dynamically recovered structures for 0.5 and 0.7% Fe alloys. With increasing Fe contents, the ultimate tensile strength and yield strength were remarkably improved, while the electrical conductivity was slightly decreased. Moreover, the creep resistance was greatly improved, which is attributed to the larger volume fraction of fine intermetallic particles and smaller subgrain size in the higher Fe-containing alloys. The creep threshold stress was found to increase from 24.6 to 33.9 MPa with increasing Fe contents from 0.3 to 0.7%, respectively. The true stress exponent values were close to 3 for all three experimental alloys, indicating that the creep mechanism of 8xxx alloys was controlled by dislocation glide.     

基于自校正Kalman滤波的液膜密封端面摩擦状态监测技术

声发射技术是液膜密封端面摩擦状态的有效检测方法,但是受工业背景噪声的影响,难以分离出声发射信号中所需信息。针对此问题,采用基于ARMA模型的自校正Kalman滤波技术处理声发射信号。该滤波器能在系统模型参数和噪声特性未知的情况下,收敛于稳态最优卡尔曼滤波器,因此滤波后的声发射信号的所需特征信号更突出,有利于液膜密封端面摩擦状态的检测。建立RBF神经网络,以时域、频域和时频域特征值作为输入进行网络训练,实现密封端面摩擦状态模式识别。实验结果证明,该监测方法能实时有效地识别端面摩擦状态,识别结果与电涡流直接测量得到的结果一致。     

Optimization of algal lipid extraction by mixture of ethyl acetate and ethanol via response surface methodology for biodiesel production

The effects of extraction time, extraction temperature, solvent to biomass ratio and solvent composition on lipid yield from lyophilized Chlorococcum sp. biomass using a mixture of ethyl acetate and ethanol (EAE), a new proposed solvent, were studied. Subsequently, the process conditions of extraction by EAE were optimized using Box-Behnken design (BBD). The results revealed that the extraction temperature had the greatest effect on lipid extraction efficiency, followed by volume ratio of ethyl acetate to ethanol (EA/E) and extraction time. The largest lipid extraction yield of 15.74% was obtained under the following extraction conditions: 40mL solvents per gram of biomass for 270 min with gentle stirring at 80 °C by EAE with an EA/E of 1.0. Furthermore, palmitic acid, stearic acid, oleic acid, and linoleic acid were the most abundant fatty acids in the lipids extracted, indicating the great potential of the proposed lipid extraction procedure for microalgae-based biodiesel production.     

改进型4Cr5Mo2MnV1Si压铸模块钢的球化处理

改进型4Cr5Mo2MnV1Si压铸模块钢采用传统“余热退火+正火+等温球化退火”工艺球化处理后,组织未达到技术要求,对其传统球化处理工艺做了改进,并对改进工艺处理试样的组织、硬度进行检测。结果表明,试验钢余热退火+正火+等温球化退火后,再经1010℃保温0.5 h炉冷至不同温度(820、790和760℃)保温1 h空冷处理后,显微组织均呈板条马氏体形态,基体上均匀弥散分布有碳化物颗粒,但硬度均高于400 HBW,未达到硬度小于240 HBW球化组织的要求。而经1010℃保温0.5 h空冷至室温,再820、790和760℃保温1 h回火空冷处理后,组织均为等轴铁素体上均匀分布着质点状碳化物,硬度分别为321、235和245 HBW,其中790℃回火效果最好,球化组织级别达到GB3,硬度小于240 HBW。因此,采用余热退火+正火+高温回火(790℃)代替余热退火+正火+等温球化退火可实现改进型4Cr5Mo2MnV1Si压铸模块钢的锻后球化处理。     

固溶处理对含Gd不锈钢第二相与硬度的影响

研究了不同固溶处理温度对含Gd不锈钢第二相与硬度的影响。结果表明,含Gd不锈钢在1000～1150℃固溶处理30 min后,沿晶界析出的连续第二相只发生部分熔断,大量第二相弥散分布于基体中,由“灰色”相包裹着“亮白色”相,“灰色”相元素组成及含量相对稳定。在1000～1070℃保温30 min固溶处理后,“亮白色”相的Ni几乎完全溶解,Gd浓缩富集,尺寸缩小,“灰色”相长大缓慢,部分“灰色”相形貌变为短棒状。固溶温度升高至1150℃,“亮白色”相中Ni溶解的同时Gd发生扩散及微量溶解,大部分“亮白色”相消失,“灰色”相发生粗化、球化。固溶处理后合金硬度均低于固溶处理前,随着固溶温度的升高,合金硬度呈上升趋势。     

非等温蠕变时效对Al-Zn-Mg-Cu合金力学性能和耐腐蚀性能的影响

研究了非等温蠕变时效处理中升温速率和峰值温度对Al-Zn-Mg-Cu合金回弹性能、力学性能和耐腐蚀性能的影响。通过透射电镜分析了合金的析出行为和时效强化机理。结果表明：随着加热速率的降低和峰值温度的升高,合金的回弹率降低;晶内析出相的尺寸增大,而体积分数先增大后减小;晶界析出相逐渐变得不连续,无析出区扩大。经非等温蠕变时效（20℃/h,180℃）处理后的合金主要析出相为致密的η’相,晶界析出相不连续,无析出区的宽度约为44.2 nm。非等温蠕变时效（20℃/h,180℃）处理的合金力学性能和耐腐蚀性能均优于常见的等温蠕变时效（120℃,24 h）处理的合金,并且时效时间缩短了67%。     

用于钯催化载体的P改性高孔隙率γ-Al2O3/α-Al2O3泡沫(英文)

提出了一种新方法来制备用于钯催化剂的P-γ-Al₂O₃涂层改性的α-Al₂O₃泡沫。采用聚氨酯模板法,通过优化工艺参数,使陶瓷泡沫的显气孔率达到90.28%,体积密度达到0.45 g·cm^-3,且该泡沫具有可使用强度。将掺有P元素的γ-Al₂O₃涂层涂覆在α-Al₂O₃泡沫上,然后通过超声波辅助浸渍法来装载活性催化相(Pd)。结果表明,含P涂层增加了惰性泡沫的比表面积和弱酸性位点,同时减少了强酸性位点的占比。与无涂层的泡沫相比,改性的泡沫更容易装载活性相,且装载的金属Pd不容易被氧化,CO的催化转化温度(T₅₀,T₉₀)降低了50℃左右。该研究证明了低成本改性α-Al₂O₃陶瓷泡沫在钯催化剂生产中具有极大的应用潜力。     

Seismic design and performance analysis of buckling‐restrained braced RC frame structures

Due to the stable hysteretic behavior, buckling‐restrained braces (BRBs) have been increasingly adopted in reinforced concrete (RC) frame structures to develop a dual structural system (BRB‐RCF). This study proposed an alternative strength‐based design approach that decomposes the dual BRB‐RCF system into two independent RC frame and BRB system using the BRB‐carrying story shear ratio. The design of RC frame is performed in an integrated manner by considering the BRB postyielding force demands. Three RC frames with five, 10, and 15 stories were employed as prototype structures, and seven story shear ratios ranging from 0.1 to 0.7 were used to generate a total of 21 structural modes. The material usage, maximum axial compression ratio of columns, and elastic interstory drift ratio were compared for different story shear ratios. Nonlinear dynamic analysis of the BRB‐RCFs subjected to 12 ground motions were carried out. The seismic response including the maximum interstory drift ratio, hysteretic energy dissipation ratio, and actual BRB‐carrying story shear ratio were systematically assessed for different design story shear ratios. Based on the considerations of material usage and seismic performance, it is suggested that the design BRB‐carrying story shear ratio should be in the range of 0.3 to 0.5.