Determination of Optimal Process Parameters of Friction Stir Welding to Join Dissimilar Aluminum Alloys Using Artificial Bee Colony Algorithm

This paper presents the efforts of joining dissimilar aluminum alloys (AA6351-T6 and AA6061-T6) by friction stir welding (FSW) process. FSW experiments are conducted according to the three factors five level central composite rotatable design method, and the response surface methodology was used to establish the empirical relationship between FSW process parameters such as tool rotational speed (N), tool traverse speed (S) and axial force (F), and the response variables such as ultimate tensile strength, yield strength, and percentage of elongation. The developed empirical models’ adequacies are estimated using the analysis of variance technique. This paper also presents the application of the artificial bee colony algorithm to estimate the optimal process parameters to achieve good mechanical properties of FS weld joints. Results suggest that the estimations of the algorithm are in good agreement with the experimental findings.     

Zr-Cu薄膜生长及力学性能的分子动力学模拟

根据磁控溅射实验条件, 采用分子动力学方法, 在Si(100)面上模拟沉积了三种Zr_xCu_100-x(x=50, 70和90)合金薄膜.通过计算径向分布函数(RDF)及X射线衍射(XRD)分析了沉积薄膜的形貌结构, 并探讨了玻璃形成能力和五重局部对称性之间的关系.最后研究了沉积薄膜的力学性能, 及薄膜厚度对拉伸过程的影响.研究结果表明: Zr-Cu合金玻璃形成能力与五重局部对称性之间存在一定的相关性, 沉积玻璃薄膜比晶体薄膜表现出更好的延展性, 其中Zr₅₀Cu₅₀沉积玻璃薄膜比近共晶成分玻璃薄膜(Zr₇₀Cu₃₀)具有更大的拉伸强度; 沉积薄膜存在一定的尺寸效应, 薄膜相对厚度越小, 其拉伸强度越大.      

400 MPa级C-Mn钢控轧控冷生产过程组织-性能的预测

建立了C－Mn钢在控制轧制和控制冷却生产中微观组织演变和力学性能预测的物理冶金模型，模型包括加热、再结晶、相变和力学性能四部分，分别描述了带热轧及冷却过程中的物理冶金现象，根据现场数据，计算了轧制过程奥氏体晶粒尺寸和再结晶分数的演变，预测了在不同工艺条件下连续冷却转变各相的体积分数和铁素体的晶粒尺寸等显微组织参数和相关的力学性能，预测结果和实测值吻合较好。     

基于大数据的力学性能预测与工艺参数筛选

神经网络数据样本的质量影响着模型的预测精度；选择有效的工艺参数进行建模可以提高模型的训练速度，节省训练时间。针对数据样本质量和输入工艺参数的选择问题进行了研究，采用了计算马氏距离的方法剔除异常点，改善数据样本的质量。基于采集到的热轧汽车大梁板的17个工艺参数的生产数据，采用贝叶斯神经网络建立力学性能预测模型。通过采用平均影响值筛选出对力学性能影响较大的工艺参数进行建模，以简化模型。结果显示：简化后的模型取得了较高的预测精度，对于抗拉强度和屈服强度，分别有96·64％和94·96％的数据预测值和实际值相对误差在±6％以内；对于伸长率，有96·64％的数据预测值和实际值的绝对误差在±4％以内。     

Online prediction and monitoring of mechanical properties of industrial galvanised steel coils using neural networks

In galvanising line of cold rolling mill, mechanical properties, i.e. yield strength (YS) and ultimate tensile strength (UTS), are achieved by controlling the key process parameters within specified limits. In this paper, a feed-forward back-propagation artificial neural network (ANN) is proposed to predict the mechanical properties of a coil from its chemical composition, thickness, width and key galvanising process parameters. Principal component analysis is used to avoid redundancy and collinearity effects in input variables for the ANN. The model predicted the YS and UTS with an accuracy of ±10?megapascal (MPa) for 90% of the data. The model was implemented in the continuous galvanising line of Tata Steel, India. An online quality monitoring system was developed to monitor the predicted mechanical properties and process parameters of a galvanised coil. This system helps quality team in decision making.     

Microstructural and Mechanical Characterization of as Weld and Aged Conditions of AA2219 Aluminium Alloy by Gas Tungsten Arc Welding Process

In this article, Welding of AA2219 aluminium alloy using Gas tungsten arc welding process (GTAW) and evaluation of metallurgical, mechanical and corrosion properties of the joints are discussed. The weld samples were subjected to ageing process at the temperature range of 195°C for a period of 5 h to improve the properties. AA2219 aluminium plates of thickness of 25 mm were welded using gas tungsten arc welding (GTAW) process in double V butt joint configuration. The input parameters considered in this work are welding current, voltage and welding speed. Tensile strength and hardness were measured as performance characteristics. The variation in the properties were justified with the help of microstructures. The same procedures were repeated for post weld heat treated samples and a comparison was made between as weld condition and age treated conditions. The post weld heat samples had better tensile strength and hardness values on comparing with the as weld samples. Fracture surface obtained from the tensile tested specimen revealed ductile mode of failure.     

玻璃包覆纯铜微丝的力学性能

以实验室制备的玻璃包覆纯铜微丝为研究对象,对玻璃包覆纯铜微丝及去除包覆层的纯铜芯丝进行了力学性能评价和断口形貌分析.结果表明:外径45μm、包覆层厚度7.5μm和外径27μm、包覆层厚度6.0μm的玻璃包覆纯铜微丝极限拉伸载荷分别为0.268N和0.237N;纯铜芯丝的拉伸应力应变曲线表现出较低的加工硬化率,屈服强度与抗拉强度比值在0.75以上;纯铜芯丝抗拉强度随直径的减小而增大;直径10μm芯丝的平均抗拉强度可达547.9 MPa,延伸率约为2.5%;芯丝断裂模式为滑移延伸断裂.     

6061-T6铝合金薄板的搅拌摩擦焊接

采用搅拌摩擦焊(FSW)技术对1 mm厚6061-T6铝合金薄板进行了对接.研究了焊接工艺参数的范围,实验测试了焊接接头的强度、硬度和延伸率,利用金相显微镜、扫描电镜和透射电镜分析了接头的微观组织.结果表明:对于1 mm厚度6061-T6铝合金,FSW的最优工艺参数为旋转速度1 800 r·min^-1,焊接速度1000 mm·min^-1;在此参数下,接头的硬度值达到母材的80%左右,抗拉强度达到母材的103%,延伸率达到母材的54%;接头的力学性能与微观结构相符.     

Taguchi Optimisation of Friction Stir Processing Parameters to Achieve Maximum Tensile Strength of Mg AZ31B Alloy

In this investigation, the effect of friction stir processing process variables such as rotational speed, traverse speed and tool tilt angle on the tensile strength of magnesium alloy AZ31B was studied. The experiments were carried out according to the Taguchi parametric design L9 at various combinations of process parameters and statistical optimization technique ANOVA was used to determine the optimum levels and to find the percentage of contribution of the process parameters. The results indicate that the rotational speed is the most significant factor followed by the traverse speed and tool tilt angle for maximising the tensile strength of the friction stir processed magnesium alloy.     

南钢超快冷工艺技术生产X70管线钢的组织性能研究

通过扫描电子显微镜(SEM)、电子背散射衍射系统(EBSD)和透射电子显微镜(TEM)等方法,针对基于超快速冷却技术(UFC)、减量化成分及工艺设计生产的X70管线钢进行组织和性能分析研究,结果表明:试制X70管线钢的组织为典型针状铁素体,组织尺寸细小均匀,交错排列,达到了细晶强化和韧化的效果;强度、塑性、冲击韧性和厚度方向组织均匀性均好于应用传统层流冷却工艺获得的各项性能;屈服强度、抗拉强度、延伸率和冲击值等各项性能都符合质量标准,且性能稳定。以超快速冷却技术为核心的新一代TMCP工艺具有良好的应用前景。     

Differences between Tensile Properties of WAAM SS304 Components in Different Directions

Wire arc additive manufacturing (WAAM) is particularly suitable for manufacturing large metal structure components. However, the anisotropy of mechanical properties of WAAM components cannot be avoided, which makes the mechanical properties of WAAM components unstable and seriously limits its engineering application. Herein, the tensile samples for 304 stainless-steel thin-walled structures along three directions (longitudinal, diagonal, and transverse) of the deposition layer are intercepted. The mechanical properties of the components are 9.3–54.6% higher than the standard values. The samples have obvious anisotropy characteristics. Samples with diagonal direction show the best mechanical properties, which are not affected by process parameters. The better the forming quality, the higher the mechanical properties of the samples. By correlating the mechanical properties results of the samples with the microstructures, it is found that very fine dendrites grow along the deposition direction in the samples, and this unique microstructure leads to the anisotropy of the mechanical properties. Under the action of uniaxial tensile load, the growth direction of precise dendrite in the sample with diagonal direction is almost the same as the slip direction of the maximum dislocation plane, which is the reason for the excellent mechanical properties of the sample with diagonal direction.     

Shear Strength and Stiffness of Silty Sand

The properties of clean sands pertaining to shear strength and stiffness have been studied extensively. However, natural sands generally contain significant amounts of silt and∕or clay. The mechanical response of such soils is different from that of clean sands. This paper addresses the effects of nonplastic fines on the small-strain stiffness and shear strength of sands. A series of laboratory tests was performed on samples of Ottawa sand with fines content in the range of 5–20% by weight. The samples were prepared at different relative densities and were subjected to various levels of mean effective consolidation stress. Most of the triaxial tests were conducted to axial strains in excess of 30%. The stress-strain responses were recorded, and the shear strength and dilatancy parameters were obtained for each fines percentage. Bender element tests performed in triaxial test samples allowed assessment of the effect of fines content on small-strain mechanical stiffness.     

Mechanical Behavior and Size Sensitivity of Nanocrystalline Nickel Wires Using Molecular Dynamics Simulation

The mechanisms of deformation and failure in face-centered cubic (FCC) nickel nanowires subjected to uniaxial tensile loading are investigated using molecular dynamics (MD) simulation, and the size effect on mechanical properties of FCC metal nanowires is studied. Simulation reveals that the surface free energy has great influence on the deformation and failure mechanism of metal nanowires. As a result of free surfaces and their reconstruction, the surface atoms depart from the perfect crystal lattice positions, leading to the appearance of nanocavities on the surfaces that are exposed to external load. The deformation process of nanowires undergoes expansion and connection of nanocavities from surface into inner lattices. Slip occurs during the deformation process, which is consistent with experimental phenomena. Elastic stiffness, yield, and fracture strength of nickel nanowires with various cross-sectional sizes are obtained, and the size effect on these mechanical properties is further analyzed. Based on numerical results, a set of quantitative prediction formulas are proposed, and they are capable of explaining the size sensitivity of nickel nanowires on the mechanical properties. Both the elastic modulus and yield strength of nickel nanowires are in a linear relationship with respect to the logarithm of their cross-sectional size, whereas the fracture strength exhibits an inverse relationship to the exponent of cross-sectional size of nickel nanowires. By using the MD simulation, the elastic modulus, yield strength, and fracture strength of a nickel nanowire in relationship to its cross-sectional size are well predicted, and they are in remarkable agreement with experimental and available numerical results. The present study demonstrates that the adopted MD simulation is capable of simulating the mechanical behavior of nanowires with respect to their geometrical size and providing numerical data that can be used to develop the empirical formulas on the effect of various physical and geometric parameters on their mechanical properties.     

Mechanical and fatigue properties of self-piercing riveted j oints in high-strength steel and aluminium alloy

Static tensile and fatigue tests were performed on shear and tensile self-piercing riveted aluminium-steel structures to evaluate their mechanical and fatigue properties.The influences of the thickness and the strength of the high-strength steel on mechanical and fatigue performances were investigated based on the tensile and F-N curves of the joints.The results show that mechanical and fatigue properties of the shear self-piercing riveted joints are much better than those of the tensile self-piercing riveted joints.Mechanical and fatigue performances of the two joints were significantly influenced by the thickness and strength of the steel sheet, and were markedly improved when the thickness of steel sheet increased.The steel strength showed significantly different effects on shear and tensile riveted structures, i.e., when the steel strength increased, the strength of the shear structure greatly increased while the tensile structure just had a slight increase in the strength.Fatigue failure generally occurred in the sheet materials and the fa-tigue crack location changed with increasing the sheet thickness and the sheet strength.     

Thixocasting Steel Hand Tools using Al2O3‐coated Steel and Molybdenum Dies

Forging is state‐of‐the‐art for producing hand tools on an industrial scale. Due to high demands on the stiffness and the fracture toughness, high‐strength forging steels are used to provide cavity‐free components with high mechanical load capacity. Moreover, forging is a cost‐effective mass production process but, in spite of all its advantages, it has its limitations, e.g. in the freedom of designs. However, because of the extreme thermal loading (particularly with regard to permanent moulds) and the frequently unavoidable casting defects, hand tools are not cast. By means of thixocasting steel, technical difficulties can be reduced and new options are provided which allow the manufacturing of components with much higher complexity than that using forging. Through near‐net shape production, manufacturing steps and costs can be reduced. Furthermore, steels, which are difficult to forge but nonetheless have high potential for specific applications (such as high strength or corrosion resistant steels), can also be processed. In cooperation with industrial partners, X39CrMo17 stainless steel size 17 combination spanners were thixocast. Forming dies were designed and optimized by simulation, the hot forming X38CrMoV5 tool steel as well as the molybdenum alloy TZM were selected as the tool alloys. The dies were treated by a plasma nitriding process and subsequently coated with crystalline Al₂O₃ protective coatings by plasma‐enhanced chemical vapor deposition (PECVD). During the experiments, combination spanners were successfully cast in the semi‐solid state. Cast parts were heat‐treated to enhance the components' toughness, which was subsequently measured by Charpy impact and tensile tests.     

Development of high strength heavy plate A517Q for offshore platform rack

This paper introduces the research and development of high strength A517Q developed by Baosteel for platform rack,with micro-alloying adding suitable quenching and tempering process,trial thickness of 127 - 178 mm high-strength A517Q.The trial plate crossing thickness has a uniform mechanical properties, yield strength greater than 700 MPa,tensile strength than 790 MPa,the Charpy impact than 90 J at -40℃, aging impact than 69 J,has high strength and excellent low temperature impact toughness,While the plate has excellent resistance to crack tearing ability of low-temperature,NDT is less than -45℃.The Developing heavy plates had been used for manufacturing racks of 200-foot jack-up offshore platform,the performance meeting the requirements of the ABS,CCS classification societies.     

A multi-scale multi-physics modeling framework of laser powder bed fusion additive manufacturing process

A longstanding challenge is to optimize additive manufacturing (AM) process in order to reduce AM component failure due to excessive distortion and cracking. To address this challenge, a multi-scale physics-based modeling framework is presented to understand the interrelationship between AM processing parameters and resulting properties. In particular, a multi-scale approach, spanning from atomic, particle, to component levels, is employed. The simulations of sintered material show that sintered particles have lower mechanical strengths than the bulk metal because of their porous structures. Higher heating rate leads to a higher mechanical strength due to accelerated sintering rates. The average temperature in the powder bed increases with higher laser power. The predicted distortion due to residual stress in the AM fabricated component is in good agreement with experimental measurements. In summary, the model framework provides a design tool to optimize the metal powder based additive manufacturing process.     

The Influence of the Thickness and Areal Density on the Mechanical Properties of Carbon Fibre Reinforced Aluminium Laminates (CARAL)

A novel composite material consisting of a laminate of several thin aluminium sheets bonded with layers of carbon fibre mat/epoxy resin. Carbon fibre reinforced aluminium laminates (CARAL) offer specific advantageous properties such as better strength, fatigue, impact, corrosion resistance, fire resistance and weight savings. CARAL is a kind of fibre metal laminate system. In the present work, CARAL was prepared and experimental tests were conducted to evaluate the influence of the thickness and areal density on the mechanical properties of CARAL. Mechanical properties such as, the tensile strength and flexural strength of the laminates were increased with the increase in thickness and areal density. CARAL with four aluminium layers and three carbon fibre mat layers have superior strength than the laminates with lesser number of layers due to thickness of laminates and areal density.     

TA15钛合金挤压薄壁型材拉伸性能及差异性研究

针对"直接热挤压"和"热挤压+脉冲锻打"TA15钛合金薄壁型材的室温力学性能及差异开展实验研究。通过对型材不同位置切取的试样进行拉伸试验,获得了型材抗拉强度和屈服强度分布规律,并对性能数据分布的均匀性和一致性进行深入分析。结果表明,"直接热挤压"态型材的抗拉强度和屈服强度数值分布较分散,强度离散系数大于3.5%;而"热挤压+脉冲锻打"态型材的抗拉强度和屈服强度数值分布相对集中,不同批次型材之间的力学性能一致性较好,强度离散系数均小于3%。进一步分析表明,2种状态型材之间的性能差异与型材表面状态、表面细晶层和截面尺寸有关。脉冲锻打能够改善型材表面细晶层分布的均匀性和截面尺寸精度,从而改善型材力学性能分布的均匀性和一致性。     

Investigation into the Microstructure and Mechanical Properties of Thin Wall Austempered Gray Cast Iron (TWAGI)

The main aim of this investigation is to assess the mechanical properties of thin wall (3 mm thickness) copper alloyed gray cast iron. Thin wall alloyed gray cast iron specimens are subjected to austempering heat treatment at six different temperatures for four different time periods. As a result, these samples develop an ausferrite matrix with excellent mechanical properties. The resulting microstructures have been evaluated and characterized by means of optical microscope and scanning electron microscope (SEM) and X-Ray diffraction analysis. The hardness and tensile properties of all these specimens are determined and correlated with the microstructure. The hardness, tensile strength and ductility initially increase, and thereafter it decreases on longer periods of austempering. On the other hand, hardness and tensile strength decreases with increasing austempering temperature, while ductility increases.