Abstract

In this study, a simulation-based examination on the deformation mechanism in the friction stir welding (FSW) process is conducted, which may not be efficiently feasible by experiment due to severe deformation and rotation of material flow near a tool pin. To overcome the severity of distortion of plastically deforming finite element meshes in the Lagrange formulation, and an over-simplified elastic-plasticity constitutive law and contact assumption in the Eulerian formulation, the arbitrary Lagrangian–Eulerian (ALE) formulation is employed for the finite element simulations. Superior accuracy in predicting the temperature profiles and distributions of the friction stir welded aluminum alloy workpiece could be obtained compared to the results of Eulerian based simulations. In particular, the ALE based simulations could predict the sharper gradient of temperature decrease as the distance from the welding zone increases, while the Eulerian based model gives more uniform profiles. The second objective of the study is to investigate the coupling of simulation-based temperature histories into the strength prediction model, which is formulated on the basis of precipitation kinetics and precipitate-dislocation interaction. The calculated yield strength distribution is also in better agreement with experiment than that by the Eulerian based model. Finally, the mechanism of the FSW process is studied by thoroughly examining the frictional and material flow behavior of the aluminum alloy in the welded zone. It is suggested that the initially high rate of temperature increase is attributed to frictional heat due to slipping of material on the tool surface, and the subsequent saturated temperature is the result of sequential repetitive activations of the sticking and slipping modes of the softened material. The sticking mode is the main source of plastically dissipated heat by the large plastic deformation around the rotating tool pin. The present integrated finite element simulation and microstructure-based strength prediction model may provide an efficient tool for the design of the FSW process.

Graphic Abstract

中文翻译：

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基于ALE有限元模拟的搅拌摩擦焊机理及其在铝强度预测中的应用。

摘要

在这项研究中，对搅拌摩擦焊（FSW）过程中的变形机理进行了基于模拟的检查，由于严重的变形和靠近工具销的材料流动，该实验可能无法通过实验有效地进行。为了克服拉格朗日公式中塑性变形有限元网格变形的严重性，以及欧拉公式中过于简化的弹塑性本构律和接触假设，对有限元采用任意拉格朗日-欧拉（ALE）公式模拟。与基于Eulerian的模拟结果相比，在预测搅拌摩擦焊接铝合金工件的温度曲线和分布方面具有出色的准确性。尤其是，基于ALE的模拟可以预测随着距焊接区域距离的增加，温度下降的梯度会越来越大，而基于Eulerian的模型给出的轮廓更加均匀。该研究的第二个目标是研究基于模拟的温度历史与强度预测模型的耦合，该模型是基于降水动力学和降水-位错相互作用而制定的。计算出的屈服强度分布也比基于欧拉模型的实验与实验更好地吻合。最后，通过彻底检查铝合金在焊接区的摩擦和材料流动行为，研究了FSW过程的机理。建议最初的高升温速率归因于材料在工具表面上的滑动而产生的摩擦热，随后的饱和温度是软化材料的粘着和滑动模式连续重复激活的结果。粘着模式是通过旋转工具销周围的大塑性变形来产生塑性散热的主要来源。本集成的有限元模拟和基于微结构的强度预测模型可以为FSW工艺的设计提供有效的工具。粘着模式是通过旋转工具销周围的大塑性变形来产生塑性散热的主要来源。本集成有限元仿真和基于微结构的强度预测模型可以为FSW工艺的设计提供有效的工具。粘着模式是通过旋转工具销周围的大塑性变形来产生塑性散热的主要来源。本集成有限元仿真和基于微结构的强度预测模型可以为FSW工艺的设计提供有效的工具。

图形摘要