Restirring and Reheating Effects on Microstructural Evolution of Al–Zn–Mg–Cu Alloy during Underwater Friction Stir Additive Manufacturing

Friction stir additive manufacturing (FSAM) can be potentially used for fabricating high-performance components owing to its advantages of solid-state processing. However, the inhomogeneous microstructures and mechanical properties of the build attributed to the complex process involving restirring and reheating deserve attention. This study is based on the previous research of the underwater FSAMed 7A04 aluminum alloy and adopts a quasi in situ experimental method, i.e., after each pass of the underwater FSAM, samples were taken from the build for microstructural observation to investigate the restirring and reheating effects on microstructural evolution during the underwater FSAM. Fine-grain microstructures were formed in the stir zone during the single-pass underwater FSAM. After restirring, the grain size at the bottom of the overlapping region decreased from 1.97 to 0.87 μm, the recrystallization degree reduced from 74.0% to 29.8%, and the initial random texture transformed into a strong shear texture composed of the C {110}<11¯0>. After reheating, static recrystallization occurred in the regions close to the new additive zones, increasing the grain size and recrystallization degree. This study not only revealed the microstructural evolution during the underwater FSAM but also provided a guideline for further optimization of the mechanical properties of the Al–Zn–Mg–Cu alloy build.     

Contact-Free Support Structures for the Direct Metal Laser Melting Process

Although Direct Metal Laser Melting (DMLM), a powder bed fusion (PBF) Additive Manufacturing (AM) for metallic materials, provides many advantages over conventional manufacturing such as almost unlimited design freedom, one of its main limitations is the need for support structures beneath overhang surfaces. Support structures are generally in contact with overhang surfaces to physically prop them up; therefore, they need to be removed after manufacturing due to not constituting a part of the main component design. The removal of supports is a process sequence adding extra time and cost to the overall manufacturing process and could result in damaging the main component. In this study, to examine the feasibility of contact-free supports for overhang surfaces in the DMLM process, coupons with these novel types of supports were prepared from CoCrMo alloy powder. This study aims to understand the effect of two parameters: the gap distance between supports and overhang surfaces and the inclination angle of overhang surfaces, on the surface topography and microstructural properties of these surfaces. Visual inspection, roughness measurements, and optical microscopy were utilized as characterization methods The roughness parameters (Ra, Rq, and Rz) were obtained using the focus variation method, and optical microscope analysis was performed on the cross-sections of the overhang surfaces to investigate the sub-surface microstructure and surface topology. Results showed that contact-free supports have a positive effect on decreasing surface roughness at all build angles when the gap distance is correctly set to avoid sintering of the powder in between the overhang and supports or to avoid too large gaps eliminating the desired effect of the higher thermal conductivity.     

某铝电公司铝合金项目扩建工程职业病危害预评价

目的识别、分析某铝电公司铝合金项目及配套预焙阳极系统的建设项目在生产过程中可能产生的职业病危害因素。方法采用检查表法与类比法相结合的原则对该建设项目进行评价。结果该项目的选址、总体布局、生产工艺和设备布局、建筑卫生学要求、辅助用室等符合国家有关法规。主要存在氧化铝尘、氟化氢、二氧化硫、噪声、工频电磁场、高温、热辐射、沥青烟等职业病危害因素。类比企业车间粉尘TWA检测,仅铸造车间清包操作位超标2.52倍。该项目属于职业病危害严重的建设项目。结论该项目在生产过程中可能产生的职业病危害是可以预防的,从职业卫生角度分析该项目是可行的。     

Corrosion Behavior of Al Modified with Zn in Chloride Solution

Aluminum-based alloys have been considered candidate materials for cathodic protection anodes. However, the Al-based alloys can form a layer of alumina, which is a drawback in a sacrificial anode. The anodes must exhibit uniform corrosion to achieve better performance. Aluminum can be alloyed with Zn to improve their performance. In this sense, in the present research, the electrochemical corrosion performance of Al-xZn alloys (x = 1.5, 3.5, and 5 at.% Zn) exposed to 3.5 wt.% NaCl for 24 h was evaluated. Polarization curves, linear polarization resistance (LPR), and electrochemical impedance spectroscopy (EIS) were used to identify the electrochemical behavior. The microstructure of the samples before the corrosion assessment was characterized by means of X-ray diffraction analyses (XRD) and scanning electron microscopy (SEM). In addition, microstructures of the corroded surfaces were characterized using X-ray mappings via SEM. Polarization curves indicated that Zn additions changed the pseudo-passivation behavior from what pure Al exhibited in a uniform dissolution regime. Furthermore, the addition of Zn shifted the corrosion potential to the active side and increased the corrosion rate. This behavior was consistent with the proportional decrease in polarization resistance (R_p) and charge transfer resistance (R_ct) in the EIS. The analysis of EIS was done using a mathematical model related to an adsorption electrochemical mechanism. The adsorption of chloride at the Al-Zn alloy surface formed aluminum chloride intermediates, which controlled the rate of the process. The rate constants of the reactions of a proposed chemical mechanism were evaluated.     

Structure,Mechanical and Magnetic Properties of Selective Laser Melted Fe-Si-B Alloy

Original 1CP powder was studied and it was founded that powder material partially consists of the amorphous phase, in which crystallization begins at 450 °C and ends at 575 °C. Selective laser melting parameters were investigated through the track study, and more suitable ones were found: laser power P = 90, 120 W; scanning speed V = 1200 mm/s. Crack-free columnar elements were obtained. The sample obtained with P = 90 W, contains a small amount of amorphous phase. X-ray diffraction of samples shows the presence of α-Fe(Si) and Fe₂B. SEM-image analysis shows the presence of ordered Fe₃Si in both samples. Annealed samples show 40% less microhardness; an annealed sample containing amorphous phase shows higher soft-magnetic properties: 2.5% higher saturation magnetization, 35% higher residual magnetization and 30% higher rectangularity coefficient.     

First-Principles Study of Silicon–Tin Alloys as a High-Temperature Thermoelectric Material

Silicon–germanium (SiGe) alloys have sparked a great deal of attention due to their exceptional high-temperature thermoelectric properties. Significant effort has been expended in the quest for high-temperature thermoelectric materials. Combining density functional theory and electron–phonon coupling theory, it was discovered that silicon–tin (SiSn) alloys have remarkable high-temperature thermoelectric performance. SiSn alloys have a figure of merit above 2.0 at 800 K, resulting from their high conduction band convergence and low lattice thermal conductivity. Further evaluations reveal that Si_0.75Sn_0.25 is the best choice for developing the optimum ratio as a thermoelectric material. These findings will provide a basis for further studies on SiSn alloys as a potential new class of high-performance thermoelectric materials.     

Mechanical Modeling of Tube Bending Considering Elastoplastic Evolution of Tube Cross-Section

Aluminum alloy tubes are widely used in various industries because of their excellent performance. Up to now, when the tube is bent, the elastoplastic deformation evolution mechanism of the cross-section has not been clear, and no direct analytical proof has been found. In this paper, based on the bilinear material model assumption, a new mechanical model of tube plane bending deformation is constructed. The analytical model can describe in detail the evolution mechanism of elastic–plastic deformation on the cross-section of the tube after bending deformation, the position of the elastic–plastic boundary, the position of the radius of the strain neutral layer, and the relationship between the bending moment over the section and the bending radius. According to this model, the deformation law of the tube cross-section during bending is elucidated. The results are as follows: (1) the deformation evolution of the cross-section of the bending deformed tube calculated by the analytical model is in good agreement with the finite element model (FEM) of pure bending. (2) By comparing the results of the analytical model with FEM results, and the processing test of the self-designed four-axis free bending forming tube bender, the bending moments are in good agreement. (3) Compared with the bending moments calculated by several other analytical models of tube bending, this model has a relatively small deviation value.     

Local Electrochemical Corrosion Properties of a Nano-SiO2/MAO Composite Coating on an AM60B-Mg Alloy

In order to improve the corrosion resistance of the automotive AM60B-Mg alloy, a nano-SiO₂/MAO composite coating was prepared on the surface of the alloy. The electrochemical properties were studied in an 80 °C corrosion environment using potentiodynamic polarization tests. Local Electrochemical Impedance Spectroscopy (LEIS) was used to study the corrosion mechanisms of coating defect zone. The microstructure and phase of the samples were observed by confocal laser microscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD). Macroscopic electrochemical test results showed that the impedance of the nano-SiO₂/MAO coating was much higher than that of the MAO coating, by about 433 times. Local electrochemical test results showed that the minimum impedance of the nano-SiO₂/MAO coating was 1–2 orders of magnitude higher than the maximum impedance of the MAO coating. The defective SiO₂/MAO coating still had high corrosion resistance compared to the defective MAO coating. A physical model of local corrosion mechanisms was proposed.     

脑复聪对脑缺血小鼠脑内SOD和GSH-Px的影响

目的探讨自拟中药方--脑复聪颗粒对脑缺血小鼠记忆能力及大脑皮层超氧化物歧化酶(SOD)和谷胱甘肽过氧化物酶(GSH-Px)活性的影响.方法采用双颈总动脉闭塞-缺血-再灌术造成学习记忆障碍小鼠模型.小鼠记忆能力以Morris圆形水迷宫的潜伏期作为指标.结果小鼠脑缺血后7 d潜伏期[(82.3±32.0)s]比假手术组[(35.3±37.9)s]延长(P＜0.01);脑复聪组[(30.6±31.3)s]恢复正常(P＜0.01).脑缺血小鼠大脑皮层SOD和GSH-Px活性(68.59±2.55,10.88±1.01)比假手术组(79.68±5.69,13.09±2.53)降低,脑复聪及当归芍药散治疗组提高到正常水平(77.56±4.88,13.35 ± 3.38;75.77±6.88,13.32±2.69)(P＜0.05～0.01).结论脑复聪颗粒对脑缺血所致的智能障碍有保护作用,其机制可能与提高SOD和GSH-Px活性、对抗自由基损伤有关.     

Sukkari dates seed improves type-2 diabetes mellitus-induced memory impairment by reducing blood glucose levels and enhancing brain cholinergic transmission: In vivo and molecular modeling studies

Cognitive decline is one of the serious complications associated with diabetes mellitus (T2DM) of type-2. In this reported work, the effect of aqueous sukkari dates seed extract (ASSE) was evaluated in T2DM-induced rats. T2DM was induced using intraperitoneal injection of nicotinamide and streptozocin (STZ) administration. The diabetic rats were then treated orally with 200 mg/kg and 400 mg/kg of dates seed extract for 30 days and results were compared with metformin-treated groups. The memory functions were assessed using three maze models. Glucose and insulin levels in the blood and acetylcholine, acetylcholinesterase brain homogenates were estimated. The results showed a significant reduction in transfer latency (TL) (p < 0.001) during the elevated plus maze (EPM) test. The novel object recognition (NOR) test revealed a longer exploration time (p > 0.05) with novel objects and a higher discrimination index (p > 0.05). The Y-maze test also showed a significant increase in the number of entries to the novel arm (p > 0.05) and the total number of entries in the trial (p > 0.01) as well as in test (p > 0.05) sessions. Reduction in blood glucose (p > 0.05) and improvement in blood insulin (p > 0.05) levels were also noted. Improvement in ACh levels (p > 0.001) with 400 mg/kg of ASSE and reduction in AChE (p > 0.001) with both doses of ASSE were also observed in the brain homogenates. The results of ASSE were found comparable with the metformin-treated rats. The estimation of phytochemical constituents displayed a significant presence of phenolic content. Further, molecular modeling studies showed ellagic acid, catechin, and epicatechin as the potential molecule interacting with GSK-3β, α-amylase, and AChE and may be responsible for observed bioactivity. In conclusion, ASSE has the ability to alleviate T2DM-related cognitive impairments.