铝合金搅拌摩擦焊温度场数值模拟及参数影响分析

对10 mm厚6061-T6铝合金,应用有限元软件COMSOL建立了搅拌摩擦焊有限元模型,模拟搅拌摩擦焊稳态温度场并分析焊速、转速变化对温度场影响。结果表明:温度分布曲线在x、y方向呈非对称的M型,返回侧峰值温度比前进侧峰值温度低约10℃,搅拌头后侧峰值温度比搅拌头前侧峰值温度高约25℃;焊接速度越大,峰值温度差值越大,转速越大,峰值温度差值也越大。焊接速度不变,转速等值增加时,x、y方向温度分布曲线等值上移,具有一定的平行性和相似性。转速不变,焊接速度等值增加时,x、y方向温度分布曲线以越来越小值下移。与转速相比,焊接速度改变对椭圆形的热影响区改变大,对椭圆率改变明显,对温度场影响显著。     

钢管径向摩擦焊温度场数值模拟

采用ABAQUS有限元软件,基于传热学及弹塑性力学有限元法,建立了径向摩擦焊接过程的二维轴对称、热力耦合及非耦合有限元计算模型.采用网格重划分技术模拟了径向摩擦焊接过程中焊接接头的温度场分布.结果表明,模拟出的接头飞边形貌与实际结果吻合良好.在二级摩擦阶段,摩擦界面由摩擦生成的热量与飞边形成带走的热量以及热传导散失的热量达到动态平衡,界面温度稳定在1320℃以下.在三级摩擦阶段,由于高温金属层被迅速挤出,界面温度迅速下降.通过分析金相组织,得出接头热循环过程.接头温度分布的模拟结果与实际结果吻合良好.     

铝-铜异种材料对接搅拌摩擦焊温度场数值模拟

根据铝-铜异种材料对接搅拌头偏置搅拌摩擦焊接特点,利用ANSYS软件,模拟焊接过程中的瞬态变化温度场以及焊缝区域各点的热循环曲线. 通过对比分析了移动焊接稳定阶段焊缝横向、纵向及厚度方向各点的最高温度变化;对比不同焊接参数的变化对焊接温度变化的影响,确定主要影响因素为搅拌头转速. 通过试验采集特征点热循环曲线与模拟比较的结果吻合度良好,验证了热源模型与散热模型的准确性. 温度场模拟结果表明,异种材料偏置搅拌摩擦焊过程中温度最高值出现在焊缝中心偏铝合金侧位置.     

铝/镁异种金属搭接搅拌摩擦焊接温度场数值模拟研究

利用有限元分析软件ABAQUS对铝/镁异种金属搭接搅拌摩擦焊温度场进行模拟研究,计算了焊接过程中不同焊接参数对温度场的影响.结果表明:数值模拟结果与测量结果能够较好吻合,热源模型的建立基本符合搅拌摩擦焊接过程,验证了已建立的模型的可靠性.     

保压腔对异种金属摩擦焊擦过程的影响

两种强度相差较大的异种金属进行摩擦焊接时，使用保压腔是克服由于软金属的大量塑性变形而给焊接过程带来困难的有效手段之一。本文研究了保压腔参数的变化对摩擦压力和摩擦扭矩的影响规律，并在合适的保压腔参数下得到了高强度的紫铜的焊接接头。     

基于Fluent的钢-铝异种金属搅拌摩擦焊数值模拟研究

建立Q235钢和6061铝合金异种金属搅拌摩擦焊的流体力学模型,基于Fluent仿真研究了不同工艺参数对钢-铝焊接的温度场、压力场、搅拌头磨损的影响规律及作用机制。结果表明:轴肩和搅拌针底面温度较高,靠近中部区域温度逐渐降低,最高温度分布在钢接触区,并随搅拌头转速的提高而增大,随焊速的提高而减小;搅拌头的高压区均分布在搅拌头旋转的前进侧,压力沿针长呈非均匀分布,最大压力位于钢接触区,压力值随焊速的提高而增大,随转速的提高而减小;受钢件挤压的影响,搅拌头的磨损主要发生在搅拌针的端部和轴肩部位。     

曲面件搭接接头搅拌摩擦焊温度场的数值模拟及参数优化

采用点点之间连接的方法实现了曲面结构件的搅拌摩擦焊焊接热源模型的加载,研究了飞机中蒙皮与桁条结构的搅拌摩擦焊搭接接头温度场的动态变化过程.结果表明,随着焊接速度的减小、旋转速度的增加以及搅拌头压力的提高,搅拌摩擦焊过程中的温度峰值升高,焊缝区域的高温区域扩大.从提高材料流动性以及避免出现熔焊的角度,提出了搅拌摩擦焊焊接工艺参数的优化方案.     

轻质异种材料摩擦焊研究现状

由于异种材料物理、化学性能及力学性能方面存在显著差异,导致其在焊接过程中容易出现被氧化、形成脆性金属间化合物、焊接变形严重等焊接缺陷。而摩擦焊作为一种绿色固相连接技术,因其焊接温度低、焊接质量好、焊接过程稳定等优点,已经在异种材料焊接中得到了广泛的应用。详细综述了异种材料搅拌摩擦焊、线性摩擦焊轴向摩擦焊的国内外研究进展,涉及到焊接工艺、力学性能和成分分析等方面,着重介绍了铝合金、镁合金、钛合金等轻质材料之间的摩擦焊接,并对今后的发展进行了展望。     

保压腔对异种金属摩擦焊塑性变形层影响

采用中断试验方法，研究两种强度相差较大的金属磨擦焊时，保压腔对塑性变形层形成，扩展及其厚度等特征的影响，揭示了保证腔条件下强度相差较大的异种金属摩擦焊的机理，扩大了摩擦焊的应用范围。     

异种金属摩擦焊接工艺参数优化算法

针对当前摩擦焊接工艺参数获取存在盲目性,提出在获得摩擦焊接工艺参数的预测范围基础上,结合正交试验进行分组.用一维有限差分的方法来对每组试验进行验证,对获得优异的工艺参数给出一维温度场,其结果与现有文献基本相符,从而证明了本算法的可行性.文中所提出的异种金属摩擦焊接工艺参数优化算法,对于实际生产中摩擦焊接工艺参数的制定,...     

Role of nickel as an interlayer in dissimilar metal friction welding of maraging steel to low alloy steel

Continuous drive friction welding of dissimilar metals, maraging steel and low alloy steel was carried out. It was observed that the hardness, ductility and impact toughness of maraging steel are low due to the diffusion of elements such as carbon, manganese, silicon and phosphorus from low alloy steel to maraging steel. An attempt was made in this study to improve the properties by friction welding of maraging steel and low alloy steel with nickel as an interlayer. The hardness, tensile strength and impact toughness are observed to be improved, as nickel acted as diffusion barrier. The effect of post-weld heat treatments on microstructure and mechanical properties of dissimilar metal friction welds with and without interlayer was also studied. Maraging steel responded to solutionizing & aging and low alloy steel responded to quenching and tempering. The notch tensile strength and impact toughness in case of dissimilar metal weld with interlayer are observed to be more than that of the dissimilar metal weld without interlayer.     

Effects of use of higher strength interlayer and external cooling on properties of friction stir welded AA6061-T6 joints

Although sound AA6061-T6 joints can be produced by friction stir welding, a loss in strength takes place in the weld region. In this study, it was demonstrated that the strength of the nugget could be increased by the use of a higher strength interlayer during friction stir welding. This strength recovery cannot, however, be attainable in the heat affected zone. Although an external cooling was applied during welding in order to increase strength in the heat affected zone, it was not sufficient for achieving the required cooling condition for improved strength.     

Modelling thermal cycles and intermetallic growth during friction melt bonding of ULC steel to aluminium alloy 2024-T3

Abstract

Dissimilar materials, aluminium 2024-T3 and ultralow carbon steel, have been welded by a novel process called friction melt bonding. A finite element thermal model is developed to predict temperature cycles and to estimate the fusion pool geometry and the intermetallic bonding layer thickness. The total mechanical power input in pseudo-steady state is inferred from in situ measurements at the tool torque and rotational speed. Temperature dependent properties, including the latent heat of fusion, and proper contact conditions between the welded plates and the backing plate are included. Predicted temperatures are in agreement with the measurements at various distances from the weld centreline. Molten pool geometries and intermetallic thicknesses, whose control is crucial to insure good weld mechanical performances, are also in accordance with the experimental observations.     

Thermal history in UNS S32205 duplex stainless steel friction stir welds

Consolidated UNS S32205 duplex stainless steel joints welds were performed using a friction stir welding (FSW) process. An experimental set-up was used to record the thermal history of duplex stainless steel FSW joint. For points at equal distance from the weld centreline, temperature measured near the beginning of the weld was lower than that measured in the middle of the welded joint. This was attributed to a non-stationary transfer condition. FSW thermal cycle showed shorter time spent at elevated temperature compared that presented by fusion welding, indicating less propensity to detrimental second phase precipitation. To support temperature measurements with thermocouples, a three-dimensional finite element thermal model of FSW was implemented, which provided a good agreement with experimental data.     

Impact of Friction Stir Welding (FSW) Process Parameters on Thermal Modeling and Heat Generation of Aluminum Alloy Joints

Friction stir welding(FSW)is a solid-state joining process,where joint properties largely depend on the amount of heat generation during the welding process.The objective of this paper was to develop a numerical thermomechanical model for FSW of aluminum–copper alloy AA2219 and analyze heat generation during the welding process.The thermomechanical model has been developed utilizing ANSYS~ APDL.The model was verified by comparing simulated temperature profile of three different weld schedules(i.e.,different combinations of weld parameters in real weld situations)from simulation with experimental results.Furthermore,the verified model was used to analyze the effect of different weld parameters on heat generation.Among all the weld parameters,the effect of rotational speed on heat generation is the highest.     

A thermal model of friction stir welding in aluminum alloys

A thermal model of friction stir welding was developed that utilizes a new slip factor based on the energy per unit length of weld. The slip factor is derived from an empirical, linear relationship observed between the ratio of the maximum welding temperature to the solidus temperature and the welding energy. The thermal model successfully predicts the maximum welding temperature over a wide range of energy levels but under predicts the temperature for low energy levels for which heat from plastic deformation dominates. The thermal model supports the hypothesis that the relationship between the temperature ratio and energy level is characteristic of aluminum alloys that share similar thermal diffusivities. The thermal model can be used to generate characteristic temperature curves from which the maximum welding temperature in an alloy may be estimated if the thermal diffusivity, welding parameters and tool geometry are known.     

Reducing bubbles in friction lap welded joint of magnesium alloy and polyamide

The direct joining between AZ31B Mg alloy and MC Nylon 6 using friction lap welding (FLW) was performed over a wide range of welding parameters to clarify the effect of welding parameters on bubble formation for the purpose of obtaining high strength hybrid joints without bubbles. The volume of bubbles in the FLW joints was influenced by the amount of gases generated due to the pyrolysis of Nylon 6 and the amount of gases squeezed out of the joints during welding. An appropriate increase in welding speed, tool rotation rate and plunge depth can reduce the volume of bubbles. Strong FLW joint with area fraction of bubbles <8% was obtained after welding process optimisation.     

Influence of B site substituent Ti on the structure and thermophysical properties of A2B2O7-type pyrochlore Gd2Zr2O7

Since the structural integrity of A₂B₂O₇-type pyrochlores relies mostly on the interconnecting BO₆ octahedra, Ti⁴⁺ was selected to partially substitute Zr⁴⁺ in Gd₂Zr₂O₇ in order to distort the pyrochlore structure in order to improve the material’s thermophysical properties for potential use as high-temperature thermal insulation. As evidenced by X-ray diffraction and Raman spectroscopy studies, incorporation of Ti⁴⁺ simultaneously leads to long-range ordering of the pyrochlore structure as well as local lattice distortion. These two effects have been shown to be competitive in determining the crystal energy of the Gd₂(Zr_1−xTi_x)₂O₇ series and result in a minimum value of the Young’s modulus at x = 0.3 and a maximum value of the coefficient of thermal expansion at x = 0.2. At lower temperatures, the thermal conductivity of Gd₂Zr₂O₇ was significantly reduced by Ti⁴⁺ doping, and its composition dependence was accurately modeled by taking into account the phonon scattering by mass and strain fluctuations at the B site.     

Filling exit holes of friction stir welding lap joints using consumable pin tools

Abstract

In this study, filling friction stir welding was used to remove the exit hole of friction stir welding lap joints made from AA5456 sheets. For this purpose, the exit holes were filled by consumable pins with various geometries and different pin applying methods. Then, the structures and mechanical properties of the resulting joints were investigated. Results showed that the strength of 7% higher than the strength of the joint with the non-filled exit hole, ～91% of the corresponding defect free joints, is obtainable with this technique. The best results were found by a pin with 11° cone angle, 8?mm diameter and 7?mm length, and with a 6?mm plunge without rotation.