Effect of powder thixoforging process on microstructural and mechanical properties of recycled 520 aluminum alloy

In this paper, reusing Al alloy chips via novel recycling process of powder thixoforging (PTF) is presented. PTF is a direct machining chips conversion method with partial melting into high quality final products with improved mechanical properties compared to parent alloy. 520.0 Al alloy powders from milling chips were produced via mechanical alloying (MA). The PTF product exhibited remarkable combination of mechanical properties of 168 HV hardness, compression yield strength (CYS) of 515 MPa, ultimate compression strength (UCS) of 1121MPa, and substantial fracture plastic strain of 45 %. Additionally, the PTF product showed relative weight reduction of 55.7 %. As a consequence, the microstructure refinement and modification during PTF have significant effects on dramatic improvement of mechanical properties, leading to considerable combination of superior strength and ductility.     

Experimental investigations on the microstructure and mechanical properties of sinter-forged Cu and Mo-alloyed low alloy steels

The present investigation pertains to the study of the mechanical properties and fracture behavior of sinter-forged low alloy steels containing copper (Cu) and molybdenum (Mo) as alloying elements. Elemental powders of atomized iron, graphite, molybdenum, and copper were mixed in suitable proportions using a ball mill, compacted in a 1,000 kN hydraulic press using suitable cylindrical die–punch combination and sintered at 1,000 ± 10°C in a muffle furnace for a period of 120 min in order to yield the alloy compositions (by weight) such as Fe–0.5% C, Fe–0.5% C–1% Cu, Fe–0.5% C–2% Cu, Fe–0.5% C–1% Mo, and Fe–0.5% C–2% Mo. The sintered cylindrical preforms were then subjected to hot upset forging to near theoretical density and subsequently machined off to standard size in order to carry out the mechanical tests such as hardness, tensile, and impact tests. Addition of Cu and Mo to the plain carbon steel has been observed to enhance the tensile strength as well as hardness of the sinter-forged alloys. The presence of Mo carbides in the microstructure of the alloys further reinforces this observation. The impact strength of this alloy has been observed to be reduced considerably due to the addition of the alloying elements.     

Investigation of the effect of diffusion bonding parameters on microstructure and mechanical properties of 7075 aluminium alloy

In the present study, diffusion bonding of aluminium alloy (AA7075) sheet materials which are used especially in the automobile and aerospace industry has been investigated at temperatures of 425 and 450 °C and pressures of 2 and 3 MPa for 180 min in argon atmosphere. The microstructural and mechanical properties of bonding have been characterized with different welding parameters such as bonding temperature and pressure. The microstructure was characterized by light optical microscope, scanning electron microscope and energy dispersive spectroscopy, while the mechanical properties were determined by tensile-shear tests and microhardness tests. The results obtained are discussed from both the microstructural and mechanical points of view. It was observed in the microstructural investigations that the interfacial oxide layer decreased with increasing of the bonding temperature and pressure. The maximum shear strength was found to be 131 MPa for the Al 7075 sample bonded at 450 °C and 3 MPa for 180 min. It is shown that in certain extent, the bonding temperature and bonding pressure have great effect on the joint shear strength. With the increasing of bonding temperature and pressure, the shear strength of the joints increases due to diffusion of atoms in the interface. The strength achieved after bonding were dependent on interface grain boundary migration and on grain growth during the bonding process. The maximum hardness value of the Al 7075 sample bonded at 450 °C, 3 MPa for 180 min is 92.5 HV_0.2. Increasing hardness with increasing temperature can be attributed to the formation of metallic bond at high temperatures and pressures.     

拼焊板焊缝力学性能实验研究

介绍了一种测量拼焊板焊缝性能的试验方法。对拼焊板进行了单向拉伸实验,并基于等应变假设,结合焊缝平行于拉伸方向的差厚拼焊板的单向拉伸试验数据,计算了焊缝的力学性能参数,分析了所得焊缝力学性能对试样尺寸和焊缝几何尺寸测量精度的敏感程度,最后通过模拟和试验结果的对比,验证了该方法的实用性。     

Effects of deformation parameters on the final microstructure and mechanical properties in warm rolling of a low-carbon steel

The effects of warm rolling parameters on the final microstructure and mechanical properties of a low-carbon steel were investigated. In doing so, the steel strips were pre-heated at various temperatures and rolled at different reductions and rolling speeds. Then, microstructural studies were performed and, also, the mechanical properties of the rolled samples were measured by tensile and hardness testing. An optimum rolling program was determined with the aids of experimental results and a mathematical model based on the finite element method (FEM) developed for the warm rolling conditions. The results show that, at high temperatures and low rolling speeds, the roll forces are reduced; however, the possibility of strain inhomogeneity and non-uniformity in the grain size distribution are increased. On the other hand, at very low temperatures, the roll force increases sharply. For the case of the employed steel, a temperature between 550–700°C and a rolling speed of 55–70 (rpm) are found to be the suitable rolling conditions for producing warm-rolled steels with uniform and fine-grain structures.     

Experimental investigation of the effect of vibration on mechanical properties of 304 stainless steel welded parts

Some of the problems that occur during the welding process include the creation of coarse grains in the weld structure and the hardening of the weld region, which reduce the strength and impact resistance of the welded parts. One technique to improve the mechanical properties of weld is the application of mechanical vibration to the molten pool. In this article, the effect of vibrating the part during welding on the mechanical properties of steel plates has been investigated in the tungsten inert gas (TIG) welding process. The plate is made of stainless steel 304 with 2 mm in thickness. A filler material has also been used for welding so that the effect of vibration can be observed on the weld pool region. The experimental tests have been performed under different welding conditions with respect to voltage, current, welding speed, vibrations amplitude, and frequency. Then, the resultant mechanical properties of the tested parts were measured. Also, the microstructure obtained by applying the vibration has been examined. Based on these experimental results, the effect of mechanical vibration on mechanical properties of the weld was investigated. Moreover, considering the mechanical properties obtained from these experiments, the optimum values of amplitude, frequency, and welding speed were determined.     

Numerical analysis and experimental investigation of modal properties for the gearbox in wind turbine

Wind turbine gearbox (WTG), which functions as an accelerator, ensures the performance and service life of wind turbine systems. This paper examines the distinctive modal properties of WTGs through finite element (FE) and experimental modal analyses. The study is performed in two parts. First, a whole system model is developed to investigate the first 10 modal frequencies and mode shapes of WTG using flexible multi-body modeling techniques. Given the complex structure and operating conditions of WTG, this study applies spring elements to the model and quantifies how the bearings and gear pair interactions affect the dynamic characteristics of WTGs. Second, the FE modal results are validated through experimental modal analyses of a 1.5 WM WTG using the frequency response function method of single point excitation and multi-point response. The natural frequencies from the FE and experimental modal analyses show favorable agreement and reveal that the characteristic frequency of the studied gearbox avoids its eigen-frequency very well.     

Experimental investigation of crack growth behaviors and mechanical properties degradation during gear bending fatigue

Journal of Mechanical Science and Technology - Tooth bending fatigue remains as a fundamental bottleneck restricting the safety and reliability of modern high-performance gear. In this study, a...     

Influence of the processing route on microstructure and mechanical properties of the polycrystalline NiAl

The influence of grain refinement on the mechanical properties of differently processed NiAl was presented. Five NiAl near‐stoichiometric alloys were investigated, three conventionally cast and two sintered from powders (fine‐grained powder made by mechanical alloying and nanopowder made by gas condensation). The mechanically alloyed and cast materials were hot extruded at different conditions to obtain diverse grain sizes. The nanomaterial was synthesized in inert gas condensation and then compacted at 1.4 GPa at 300 °C. It was shown that the ductility and strength can be directly controlled by appropriate texture and grain refinement.     

Experimental investigation of process parameters for roll-type linear chemical mechanical polishing (Roll-CMP) system

The fabrication processes for electronic components are now demanding a higher degree of planarity for integration and multistacking, with chemical mechanical polishing (CMP) processes replacing conventional etching or mechanical polishing owing to their ability to attain global planarization. As CMP has been applied to more and more fields, new types of CMP machines have been developed. This study introduces a novel roll-type linear CMP (Roll-CMP) process that uses a line-contact material removal mechanism to for the polish flexible substrates, and examines the effect of the process parameters on the material removal rate (MRR) and its nonuniformity (NU). The parameters affecting the Roll-CMP process include down force, roll speed, table feed rate, slurry flow rate, slurry temperature, and the table oscillation length. Increasing the down force, roll speed, slurry flow rate, and slurry temperature resulted in a high average MRR (MRR_avg). Further, the MRR_avg was found to decrease with an increase in the oscillation length because of the effect of the polishing area. A large down force, high roll speed, high table feed rate, and high slurry flow rate were effective for reducing the NU. These results will be helpful for understanding the newly developed Roll-CMP process.     

Effect of welding speed on microstructure and mechanical properties of friction-stir-welded aluminum

The weld properties remain an area of uncertainty with respect to the effect of different speeds of friction stir welding (FSW). For this purpose, hardened steel tool of FSW was used, which consists of the shoulder and pin. The shoulder of the tool not only provides additional heat generated by friction but also prevents plasticized material to escape. In the present investigation, aluminum welds were made at various welding speed using the FSW technique. The welds were characterized for mechanical properties and microstructural investigation. It is observed that good correlation exists between the mechanical properties and welding speeds. The best mechanical properties were obtained at lower welding speed.     

喷吹N_2、Ar对Al-Cu合金组织性能的影响

通过力学性能测试、硬度值测试和金相显微组织分析,研究了通气工艺对Al-Cu合金组织和性能的影响。结果表明:过滤后通气改善铝合金组织和性能的效果比过滤前通气的显著;而过滤后通Ar的铝合金组织均匀,析出相细小弥散,力学性能最好。其抗拉强度、延伸率和硬度值分别达到382 MPa、7.8%和115HBS10/1000/30,比未进行通气处理分别提高了48%、28%和46%。     

Effect of microstructure and mechanical properties on the seizure resistance of cast aluminium alloys

Seizure resistance of several cast aluminium base alloys has been examined using a standard Hohman Wear Tester. Disks of aluminium base alloys were run against a standard aluminium 12% silicon base alloy. The seizure resistance of the alloys (as measured by the lowest bearing parameter reached before seizure) increased with hardness, yield and tensile strength. In Al-Si-Ni alloys where silicon and nickel have little solid solubility in α-aluminium and Si and Ni Al₃ hard phases are formed, the minimum bearing parameter decreased with the parameter V (The product of vol. % of hard phases in the disk and the shoe). Apparently the silicon and NiAl₃ particles provided discontinuities in the matrix and reduced the probability (1 ? V) of the α-aluminium phase in the disk coming into contact with the α-aluminium phase in the shoe. The copper and magnesium containing Al-Si-Ni alloys with lesser volumes of hard phases exhibit considerably better seizure resistance indicating that a slight increase in the solute content or the hardness of the primary α-phase leads to a considerable increase in seizure resistance. Deformation during wear and seizure leads to fragmentation of the original hard particles into considerably smaller particles uniformly dispersed in the deformed α-aluminium matrix.     

Experimental investigation of the effect of lead errors on helical gear and bearing vibration transmission characteristics

The characteristics of gear meshing vibration undesgo change as the vibration is transmitted from the gear to the housing. Therefore, vibration transmission characteristics of helical gear systems must be understood before the effective methods of reducing gear noise can be found. In this work, using a helical gear with different lead errors, the gear vibration in the rotational direction and the bearing vibration are measured. The frequency characteristics of gear and bearing vibration are investigated and a comparson is also provided.     

Three-dimensional finite element analysis of the mechanical properties of helical thread connection

Conventional analytical and numerical methods for the mechanical properties of helical threads are relied on many assumptions and approximations and thus hardly yield satisfied results. A parameterized 3D finite element model of bolted joints with real helical thread geometry is established and meshed with refined hexahedral elements. The Von Mises plasticity criterion, kinematic hardening rule of materials and interfacial contacts are employed to make it possible for the suggested model be able to approach real assembly conditions. Then, the mechanical properties of bolted joints with different thread pitches, thread numbers and modular ratios are investigated, including the contact pressure distribution at joint interfaces, the axial load distribution and stress concentration in screw threads during the loading and unloading process. Simulation results indicate that the load distribution in screw threads produced by the suggested model agrees well the results from CHEN’s photoelastic tests. In addition, an interesting phenomenon is found that tightening the bolt with a large preload first and then adjusting the clamping force by unloading can make the load distribution more uniform and reduce the maximum residual equivalent stress in thread roots by up to 40%. This research provides a simple and practical approach to constructing the 3D finite element model and predicting the mechanical properties of helical thread connection.     

改性聚四氟乙烯材料的力学性能实验研究

为了研究改性低密度聚四氟乙烯材料的力学性能,利用万能试验机进行了准静态拉伸和压缩试验,通过霍普金森杆实验研究其在冲击载荷作用下的动态力学特性.对不同长径比改性与非改性试样在不同载荷加载下的力学特性以及不同冲击速度下的动态响应特性进行了分析.结果表明,通过在聚四氟乙烯材料中添加铜粉可以提高其抗拉强度,改善伸长率,增强抗压缩强度;随应变率的增大,改性聚四氟乙烯的屈服强度得到提高.     

冷却速率对Ti-1300合金组织转变的影响

用膨胀法和金相显微镜研究了近β钛合金Ti-1300合金在连续冷却过程中组织转变规律。结果表明:随着冷却速率的增加,Ti-1300合金的显微组织呈规律性的变化;当冷却速率较慢时,Ti-1300合金的室温组织为层片状α相和β相的组织;当冷却速度大于0.3℃/s时,在片层组织中出现了块状的残余β相并随冷却速率的增大而增多。显微硬度随冷速加快出现先增加后降低的现象。     

稀土钇的添加对铅锡青铜组织性能的影响（英文）

柱塞泵转子是液压机械中不可或缺的重要零件之一,其性能和质量决定了柱塞泵的传动效率和使用寿命。本文主要研究稀土钇对柱塞泵转子中的耐磨层的组织和性能的影响,耐磨层的材质是由铅锡青铜组成,通过加入不同含量的稀土钇,观察铅锡青铜组织和性能的变化.通过对比得出,稀土钇的添加对铅锡青铜的抗拉强度和延伸率都能有所提高,而且组织中铅颗粒形态也比不加稀土时更加细小、均匀。但是,加入量过高,抗拉强度和延伸率反而有所下降,组织中的铅颗粒也有长大的趋势.最后得出稀土的最佳添加量为0.04%时,其综合性能最好。