Effect of fabrication parameters on the pore concentration of the aluminum metal foam, manufactured by powder metallurgy process

In this paper, the effect of fabrication parameters on the pore concentration of aluminum metal foam manufactured by powder metallurgy process is studied. Aluminum metal foam specimens were fabricated from the mixture of aluminum powders (mean particle size 60 μm) and NaCl at 10,20,30,40(wt) % content under 200, 250, 300, MPa Pressures. All specimens were then sintered at 630°C for 2.5 hours in an argon atmosphere. For pore formation (foaming), sintered specimens were immersed into 70°C hot running water. Finally the pore concentration of specimens was recorded to analyze the effect of fabrication parameters (namely NaCl ratio, NaCl particle size and compacting pressure) on the foaming behavior of compacted specimens. As a result of the study, it has been recorded that the above mentioned fabrication parameters are effective on pore concentration profile while pore diameters remained unchanged.     

Multi-response optimisation of sintering parameters of Al–Si alloy/fly ash composite using Taguchi method and grey relational analysis

In this paper, an attempt has been made to optimise the sintering process parameters of Al–Si (12%) alloy/fly ash composite using grey relational analysis. Al–Si alloy/fly ash composite was produced using powder metallurgy technique. Al–Si alloy powder was homogenously mixed with various weight percentages of fly ash (5–15 wt.%) and compacted at a pressure ranging from 307 to 512 MPa. The green compacts were sintered at temperatures between 575 and 625°C. Experiments have been performed under different conditions of temperature, fly ash content, and compacting pressure. Taguchi’s L₉ orthogonal array was used to investigate the sintering process parameters. Optimal levels of parameters were identified using grey relational analysis, and significant parameter was determined by analysis of variance. Experimental results indicate that multi-response characteristics such as density and hardness can be improved effectively through grey relational analysis.     

车身复杂结构大规模问题的缩减计算

针对车身设计中复杂结构多参数大规模问题,提出了一种基于减基法和有限元的混合算法来进行缩减计算。该方法首先通过计算系统在有限个样本下的响应构造近似解空间,然后基于有限元方法分离出刚度矩阵中的设计参数,接着将矩阵向解空间进行投影,最后构建减缩计算系统。在新参数条件下,通过减缩系统得到大规模问题的响应,极大地提高了结构响应的计算效率。     

Workability studies on Al–5%SiC powder metallurgy composite during cold upsetting

The present technical work reports on the workability performance along with the consolidation behavior of aluminum (Al) and Al–5% silicon carbide (SiC) powder metallurgy composites during cold compaction. An experimental work has been carried out to investigate the powder compaction behavior of Al–SiC metal matrix composites. SiC of particle sizes 120, 75, and 45 μm has been pre-alloyed with Al powders of particle size ranging from ?37 to 75 μm. Various particle size additives of SiC have been used as a second-phase particle in this work with the intension of predicting the mechanical and metallurgical properties of the metal matrix composites studied. The pressure applied for the preparation of compacts have been considered as 220–260 kN in order to prepare the samples of heights in the range of 30 to 32 mm, and the diameter of the compacted sample was 26.11 mm. The densification during compaction is measured by means of the presence of voids in the compacts applying the mass constancy principle. The effect of particle size on the metal matrix composites proposed has been completely investigated under two different stress state conditions such as plane and triaxial.     

用铝粉作增粘剂制备泡沫铝

采用熔体发泡法制备了孔结构均匀、孔隙率高的泡沫铝材料,系统研究了铝粉(增粘剂)含量、增粘搅拌时间、保温时间和发泡剂的含量对孔隙率和孔结构的影响。对铝粉在铝熔体中的增粘机理以及在发泡过程中对气泡的稳定作用进行了讨论。结果表明:加入质量分数5％铝粉,搅拌时间7 min,发泡剂TiH2质量分数1．5％,保温5 min的条件下,可以得到孔结构均匀、孔隙率约75％的泡沫铝硅合金材料。     

Modeling adhesive wear resistance of Al-Si-Mg-/SiCp PM compacts fabricated by hot pressing process, by means of ANN

In this study, modeling adhesive wear resistance of Al-Si-Mg/SiC_p MMC compacts were performed by ANN, using a back-propagation neural network that uses gradient descent learning algorithm. Powder compacts were fabricated by PM hot pressing process with 5–10–20% SiC_p fractions and contents of specimens (N1, N2, N3 andN4) were given in Table 1. The wear tests were carried out under 10, 20 and 30 N variable loads, while disk rotation speed 90 rpm kept unchanged. Adhesive wear looses were measured and recorded for 250, 500, 1,000 and 1,500 m distances. Microstructure examination at wear surface was investigated by optical microscopy and EDS for metallographic evaluations. In neural networks training module, SiC_p reinforcement fractions (wt), loads and wear distances (m) were used as input, lost mass (g) of specimens were recorded as outputs. Then, the neural network was trained using the prepared training set (also known as learning set). At the end of the training process, the test data were used to check the system accuracy. As a result ANN was found successful in modeling of adhesive wear behavior and lost mass values of Al/SiC_p PM compacts.

Experimental and Prediction of Abrasive Wear Behavior of Sintered Cu-SiC Composites Containing Graphite by Using Artificial Neural Networks

Experimental investigations were undertaken to determine the abrasive wear behavior of various percentages of Cu-SiC-Gr hybrid composites. Wear tests were carried out using a pin-on-disc type machine using various input parameters like load, sliding distance, and sliding velocity with various SiC abrasive papers of grit size 80, 220, and 400, having an average particle size of 192, 102, and 45 μm. Neural networks are employed to study the tribological behavior of sintered Cu-SiC-Gr hybrid composites. Optical microscope, scanning electron microscope (SEM), X-ray diffraction (XRD), and energy-dispersive spectral observations are used to evaluate the characteristics. The proposed neural network model used the measured parameters, namely, the weight percentage of graphite, abrasive size, sliding speed, load, and sliding distance, to predict the wear loss of the composite. In order to improve the accuracy and obtain better results, an artificial neural network (ANN) with a genetic algorithm (GA) function was used. Optimization of the training process of the ANN using a GA is performed and the results are compared with the ANN trained without a GA. The predicted values from the proposed networks coincide with the experimental values.     

A new shell casting process based on expendable pattern with vacuum and low-pressure casting for aluminum and magnesium alloys

A new shell casting process, with the adoption of the foam pattern of lost foam casting (LFC) as prototype and the combination of the thin shell fabrication technology of investment casting and vacuum and low-pressure casting process, was proposed for manufacturing complicated and thin-walled aluminum and magnesium alloy precision castings. Loose-sand uniting vacuum was used in the new process to further reinforce the thin shell, and the new process proves to be a process with simple process, low cost, and high thin shell strength. Because the molten metal filling and solidification are completed under air pressure and vacuum level, the filling capability and feeding capacity of the molten metal are greatly improved, and the castings become denser. This paper mainly investigated the fabrication technology of thin shell based on foam pattern prototype, the removing foam and roasting shell process and vacuum and low-pressure casting process. The few-layer compound thin shell of silica sol–sodium silicate was adopted for the new process. Removing foam pattern was carried out at 250°C for 30 min, and the shell was roasted at 800°C for 1 h. Combined with the vacuum and low-pressure casting process, this new shell casting process has successfully produced thin wall and complex aluminum and magnesium alloy parts with high quality. In addition, comparisons in terms of filling ability, microstructure, mechanical properties, porosity, and surface roughness among this new shell casting, gravity casting, and LFC were also made to show the characterization of this new shell casting process.     

Study of Al-alloy foam compressive behavior based on instrumented sharp indentation technology

The stress-strain relation of aluminum (Al) alloy foam cell wall was evaluated by the instrumented sharp indentation method. The indentation in a few micron ranges was performed on the cell wall of Al-alloy foam having a composition of Al-3wt.%Si-2wt.%Cu-2wt.%Mg as well as its precursor (material prior to foaming). To extract the stress-strain relation in terms of yield stressσ _y, strain hardening exponentn and elastic modulusE, the closed-form dimensionless relationships between load-indentation depth curve and elasto-plastic property were used. The tensile properties of precursor material of Al-alloy foam were also measured independently by uni-axial tensile test. In order to verify the validity of the extracted stress-strain relation, it was compared with the results of tensile test and finite element (FE) analysis. A modified cubicspherical lattice model was proposed to analyze the compressive behavior of the Al-alloy foam. The material parameters extracted by the instrumented nanoindentation method allowed the model to predict the compressive behavior of the Al-alloy foam accurately.     

Microstructural and mechanical properties of nanometric magnesium oxide particulate-reinforced aluminum matrix composites produced by powder metallurgy method

In this research, aluminum alloy (A356.1) matrix composites reinforced with 1.5, 2.5 and 5 Vol.% nanoscale MgO particles were fabricated via powder metallurgy method. Pure atomized aluminum powder with an average particle size of 1μm and MgO particulate with an average particle size between 60 to 80 nm were used. The specimens were pressed by Cold Isostatic Press machine (CIP), and were subsequently sintered at various sintering temperatures, viz. 575, 600 and 625°C. Optimum amount of reinforcement and sintering temperature were determined by evaluating the density, microstructure and mechanical properties of composites. The composites were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Hardness and compression tests were carried out in order to identify mechanical properties. Reinforcing the Al matrix alloy with MgO particles improved the hardness and compressive strength of the alloy to a maximum value of 44 BHN and 288 MPa, respectively. The most improved compressive strength was obtained with the specimen including 2.5% of MgO sintered at 625°C. According to the experiments, a sintering temperature of 625°C showed better results than other temperatures. A good distribution of the dispersed MgO particulates in the matrix alloy was achieved.     

压制次数对铜基粉末冶金摩擦材料物理性能的影响

粉末压制是粉末冶金工艺关键步骤,压制压力直接影响着粉末冶金压坯的密度,提高压坯密度有助于提高粉末冶金制品的各项力学性能和物理性能。随着压制压力的提高,压坯密度呈现先急增后缓增的趋势,因此压制压力的大小严重影响着粉末冶金制品的性能。然而当压制压力不能使粉末冶金摩擦材料制品达到所需的压坯密度时,增加压制次数也能够在一定程度上提高压坯密度,一般情况下铜粉的屈服强度为200MPa左右,而一般铜基粉末冶金摩擦材料制品所需要的压制压力为600～800MPa,当使用低压压制时为了达到所需的压坯密度、硬度及各项物理性能,可适当增加压制次数,从而同样能达到改善压坯物理性能的目的。     

Characterization of the size distribution of subbituminous coal by laser diffraction

This article deals with effects of the selected instrument parameters on the results of the particle size distribution measured by laser diffraction. The goal of this work is to define the optimal parameters of instrument for determination of particle size distribution of subbituminous coal. The samples were analyzed by dry and wet methods. The studied parameters were the feed rate and the pressure of air. The coal sample was a fragile material and was determined by the dry method. The optimum value of the feed rate was 80% and the air pressure was 1.2 × 10⁵ Pa by application of Mie theory. The results were statistically analyzed by analysis of variance. The feed rate and air pressure were shown to influence the determination of particle size distribution by laser diffraction.     

Powder injection molding 440C stainless steel

In this work, the processing steps for producing 440C stainless steel parts by means of powder injection molding technique were investigated. The molded specimens were debinded by solvent debinding followed by thermal debinding methods and were sintered under vacuum atmosphere. Effective densification took place in the temperature range 1,230–1,240°C in the sintering. After heat treatment, specimens sintered at 1,240°C for 30 min had the tensile strength of 876.3 MPa, the hardness of 57.7 HRC. Pitting mainly occurred in injection molding 440C stainless steel specimens in NaCl solution. The content of carbon has serious effect on the shape retention. Some methods, such as preventing from oxidation, are presented to avoid the as-sintered specimens from deformation.     

Transient liquid phase (tlp) diffusion bonding of Ti45Ni49Cu6 P/M components using Cu interlayer

In this study, transient liquid phase diffusion bonding parameters of Ti₄₅Ni₄₉Cu₆ P/M components using copper interlayer were experimentally investigated in a protective (argon) atmosphere. Bonding processes of sintered Ti₄₅Ni₄₉Cu₆ P/M compacts were carried out at various temperatures and bonding periods while bonding pressure was kept unchanged. The process pressure, 20 MPa, was selected just below those which would cause macro deformations. Optical microscopy, scanning electron microscopy, and energy dispersive spectroscopy were employed for microstructure examinations. Shear strength and hardness (HB) of bonded specimens were measured at bond interface and parent materials for mechanical property evaluations. Along the bond interface, copper, titanium, and nickel atom mutual migration was observed. Structural tests, metallographic analysis have shown the integrity of the diffusion bonded hardware, bonded between 940 and 970°C process temperatures, for 40–60-min bonding periods.     

稀土对泡沫铝及泡沫铝合金耐腐蚀性能的影响

研究了稀土对泡沫铝及泡沫铝合金泡沫化和压缩性能的影响，讨论了稀土加入量和泡沫铝及泡沫铝合金耐腐蚀性能的关系。结果表明：稀土对铝合金泡沫化无异常影响；在泡沫铝和泡沫铝合金中添加适量稀土元素，可以提高泡沫铝和泡沫铝合金的耐腐蚀性能；相同腐蚀介质中，孔隙率高的泡沫铝合金腐蚀更严重；稀土对泡沫铝及其合金的力学性能影响不大。     

Fabrication and characterization of 7075 Al alloy reinforced with SiC particulates

7075 aluminum (Al) alloy as matrix and silicon carbide (SiC) as reinforcement has been identified since it has potential applications in aircraft and space industries because of lower weight to strength ratio, high wear resistance and creep resistance. Thorough investigations about the microstructure and characterization of Al alloy/SiC composite are needed so that metal matrix composites (MMCs) fabricated for aircraft and space industries are defect free and have sound microstructure. Objective of this research work are the fabrication and microstructural investigations of AA7075–SiCp MMCs. 7075 Al alloy is reinforced with 10 and 15 wt.% SiCp of size 20–40 μm by stir casting process. The resulting as-cast composite structures are analyzed using scanning electron microscopy, X-ray diffraction (XRD), differential thermal analysis, and electron probe microscopic analysis (EPMA). SiCp distribution and interaction with 7075 Al alloy matrix is studied. The 7075 Al alloy–SiCp composite microstructure showed excellent SiCp distribution into 7075 Al alloy matrix. In addition to this, no evidence of secondary chemical reactions is observed in XRD and EPMA analysis. Decomposition step in derivative thermogravimetric curve is seen at temperature of 1,257, 1,210, and 1,256 °C for 7075 Al alloy, AA7075/10 wt.%/SiCp (20–40 μm) and AA7075/15 wt.%/SiCp (20–40 μm) composites, respectively. So, these composites can be successfully used for applications where temperature does not exceed beyond 1,250 °C.     

A study of densification and on factors affecting the density of Ni x –Fe100 − x nanopowders prepared by mechanical alloying and sintered by spark plasma

Mechanical alloying through high-energy ball milling was used in the production of Ni–Fe alloy powders from elemental Ni and Fe powders of average particle size 80 and 25 μm, respectively. High-energy planetary ball milling at room temperature was performed for various time durations ranging between 2 and 100 h. SPS apparatus was used for sintering of powder particles. Density of all specimens was reported and a maximum densification of 99 % was achieved in 50 wt.% Ni–Fe milled for 16 h prior to spark plasma sintering at 1,223 K.     

Friction and wear behaviour of sintered steels submitted to sliding and abrasion tests

Fe–C–Mo and Fe–C–Cr steels were sintered by PM processes carried out using different values of temperature and pressure, leading to different microstructures and density values. Flat specimens were submitted to tribological tests in order to evaluate their behaviour under both dry sliding and abrasive wear conditions. A flat-on-cylinder tribometer was used for the sliding tests, while a micro-scale ball cratering device was used for the abrasion tests. The dry sliding wear resistance of the PM steels was mainly influenced by the composition and sintering conditions. In this regard, the best behavior was observed for the more hardenable Fe–C–Mo steels with higher Mo content, sintered under conditions giving rise to bainitic microstructures. A determining role was also played by the porosity content and pore shape: reduction in porosity (obtained by increasing the sintering temperature and the compacting pressure), as well as an increase in pore roundness, led to a significant improvement in the resistance to sliding wear. A mild oxidative wear regime were observed for all the sintered steels under relatively low values of the applied load, while an increase of the applied load led to a delamination wear regime. The resistance to abrasive wear was low for all the tested steels, irrespective of composition and sintering cycle.     

On the effect of relative size of magnetic particles and abrasive particles in MR fluid-based finishing process

Magnetorheological fluid-based finishing (MRFF) process is widely used for fabrication of optical material such as glasses, lenses, mirrors, etc. Performance of the process is significantly affected by the properties (size, concentration, hardness, etc.) of the constituents of MR fluid. MR fluids have been prepared by varying three abrasive particles mean sizes (4 µm, 6 µm and 9 µm) with carbonyl iron particles (CIPs) having average particles size of 6 µm. Yield stress of MR fluids is measured using a rheometer. The composition of the fluid has CIPs of 25%, abrasive 10% (by volume) and rest of the base medium (liquid). The yield stress was evaluated at magnetic flux density of 0.33 Tesla. It is observed that MR fluid having the same particle size of CIPs and abrasive particles exhibits higher yield stress as compared to other combinations. The lowest yield stress is observed in case of 9 µm abrasive particles size. A set of finishing experiments is carried out to understand the effect of relative size of magnetic particles and abrasive particles on surface roughness values.     

Laser shock wave treatment of polycrystalline diamond tool and nanodiamond powder compact

Laser shock processing (LSP) of polycrystalline diamond (PCD) tools and nanodiamond powder compacts was conducted using a 1,064-nm Q-switched Nd:YAG laser at peak power densities in the range of 4 to 18 GW/cm² and pulse repetition rates of 1 to 10 Hz. The PCD tools were directly procured from the tool manufacturer while nanodiamond powder compacts were prepared in the laboratory by cold die press forming and annealing using a powder mixture of nanodiamond, 8 wt.% cobalt, and 10 wt.% agar–agar as the binder. The samples were characterized by Raman spectroscopy, scanning electron microscopy, micro-indentation, and optical profilometer. Results indicate that LSP induced diamond purification, inhomogeneity of phases in PCD, densification in nanodiamond compact, phase transition to various amounts of sp³ and sp² carbon forms, and an increase in hardness and surface roughness.