Joining of Dissimilar Materials through a Novel Hybrid Friction Stir Resistance Spot Welding Process

在许多工业应用(例如，汽车、航空航天和国防工业)中，非常需要一种可靠、高效和经济的连接不同材料的方法。这种方法能够利用多材料结构并减轻车辆重量。实现可靠的异种材料接头，将为未来多材料车辆结构的设计提供指导。该奖项支持基础研究，以提供所需的知识，以创造一种新型、混合和高效的连接方法，将传统的电阻点焊方法与最近开发的搅拌摩擦工艺相结合。本研究的目的是：(1)通过电塑性增强的搅拌摩擦点焊，确定脉冲电流对异种材料焊接时的热应力场、机械应力场和材料行为的影响；(2)建立关键输入参数(如脉冲电流大小和频率、搅拌摩擦工具转速、插入速度等)之间的数学关系。以及由此产生的工艺动态和相关工艺性能指标的预测，例如接头质量、温度分布以及焊接力和扭矩。本文的研究范围包括对异种材料在点焊过程中通过搅拌摩擦法熔合的焊接区的材料流动、应力和形貌的建模和分析。将使用多物理建模方法来计算材料、温度和应力分布场。该模型还将用于分析与脉冲电流相关的电塑性和加热对熔核中材料行为的影响。多相流理论将用于描述不同材料在焊接熔核中的行为。为了量化接头质量，将进行力学试验和微观结构分析。

A reliable, efficient, and economical method for joining dissimilar materials is highly desired in many industrial applications (e.g., automotive, aerospace, and defense industries). Such a method enables utilization of multi-material structures and reduction of vehicle weight. Achievement of reliable dissimilar material joints will provide design guidance for future multi-material vehicle structures. This award supports fundamental research to provide knowledge needed to create a novel, hybrid, and highly efficient joining method that integrates traditional resistance spot welding method with recently developed friction stir process. Research results can greatly contribute to the vehicle light-weighting efforts and thus to increased fuel economy of transportation vehicles and future sustainability.The objectives of this research are: (1) to determine the effects of pulsed electric currents on the thermal and mechanical stress fields, and material behaviors when joining dissimilar materials through the use of electro-plastically enhanced friction stir spot welding, and (2) to create the mathematical relationship between key input parameters (e.g., pulsed electric current magnitude and frequency, rotational speed of friction stir tool, plunge speed, etc.) and the resulting prediction of process dynamics and the associated process performance metrics such as joint quality, temperature distribution, and welding force and torque. The scope of this research includes the modeling and analysis of material flow stress and morphology in the welding zone where dissimilar materials are fused through the friction stir technique in resistance spot welding process. A multi-physics modeling approach will be utilized to calculate the material, temperature and stress distribution fields. This model will also be utilized to analyze the effects of electro-plasticity and heating associated with pulsed electric current on material behavior in the weld nuggets. Multiple phase flow theories will be used for describing dissimilar material behaviors in the weld nugget. In order to quantify the joint quality, both mechanical tests and microstructure analysis will be conducted.