高强铝合金点焊微裂纹的智能预测与多场诱导愈合机理研究

This project is to predict the micro-cracks of the high-strength aluminum alloy in resistance spot welding by using multi-information fusion theory and to study the healing mechanism for the micro-cracks in the condition of the thermal-mechanical-electrical field. A mathematics analysis method will be built to discover the formation mechanism and influencing factors on the micro-cracks of high-strength aluminum alloy in the resistance spot welding under the quickly heating and cooling, which is based on the theory of uniform design experimentation and stepwise regression analysis. The theory and method of feature recognition, reduction and intelligent fusion will be studied, then a multi-information fusion model and algorithm will be established by using wavelet, rough set, neural network and fuzzy logic theory, which can predict the micro-crack of high-strength aluminum alloy in the resistance spot welding accurately. Based on thermodynamics of diffusion and molecular dynamics, the healing mechanism and driving force for the micro-crack of high-strength aluminum alloy in the resistance spot welding will be studied, then the effects of the external energy to the healing of the micro-crack under the high temperature, plastic deformation and electromagnetic will be discovered. This research is about a basic common problem in the many manufacture areas, such as the real-time monitoring and quality control of the welding and forging process. The research results have not only significant science significance to eliminate the micro-cracks of the high-strength aluminum alloy in the hot working process and to enhance the mechanical property and the reliability of the structure, but also benefit to develop the healing theory and technology of metallic material.

针对高强铝合金电阻点焊微裂纹的预测和愈合机理，基于均匀试验设计和逐步回归分析理论，建立高强铝合金点焊微裂纹的理论解析、描述与表征方法，揭示快速加热及冷却条件下高强铝合金点焊微裂纹的形成机制和影响因素；研究高强铝合金点焊微裂纹多信息特征鉴别、约简、智能融合理论及方法，进而建立基于小波、粗糙集、神经网络和模糊理论相结合的高强铝合金点焊微裂纹预测多信息融合模型和算法；基于扩散热力学和分子动力学理论，研究高强铝合金点焊微裂纹愈合的物理实质及原动力，揭示热-力-电等多场耦合条件下外部能量对高强铝合金点焊微裂纹愈合的作用机理。该研究是焊接、锻造等热加工领域涉及的过程实时监测及质量控制的共性基础性问题，其成果不仅对根除高强铝合金在热加工过程中的微裂纹缺陷、提高结构的综合机械性能和工作可靠性具有重要的学术意义，对发展金属材料的愈合理论与技术也有积极作用。

高强铝合金在航空航天及汽车等领域有着十分广泛的应用前景，但是由于材料塑性区窄、高温塑性差，在电阻点焊快速加热和冷却条件下极易形成裂纹等缺陷，降低了点焊接头的可靠性。目前，对于点焊接头μm级的微观裂纹尚无可靠有效的无损检测方法。基于上述背景，本项目开展了高强铝合金电阻点焊微裂纹的智能预测理论、方法和多场耦合诱导愈合机理的基础研究工作，主要研究内容包括：高强铝合金电阻点焊微裂纹形成机制及其影响因素研究；基于人工智能的高强铝合金电阻点焊微裂纹预测多信息融合理论和方法研究；多场耦合诱导高强铝合金电阻点焊微裂纹愈合机理研究；多场耦合诱导铝合金点焊微裂纹愈合行为的计算机模拟仿真研究。.项目取得了如下主要重要结果：.1、获得了预热电流、焊接电流、缓冷电流、电极压力、球面电极半径、焊接时间、电极水冷端距离等工艺参数对高强铝合金电阻点焊微裂纹的影响规律，阐明了铝合金点焊微裂纹的形成机制；.2、发明了一种可在焊接过程中实时测量动态焊接压力的传感器；.3、构建了铝合金点焊微裂纹多信息传感及智能预测系统，实现了电极压力、声发射、电极位移、焊接电流及焊接电压等信号的实时检测、显示、存档以及飞溅、裂纹等缺陷的预测功能；.4、获得了表征高强铝合金点焊微裂纹物理参数在时域、时频域的特征信息，基于多传感信息融合的铝合金点焊裂纹BP神经网络预测正确率达到97.8%；.5、发明了一种基于搅拌摩擦热力耦合效应的高强铝合金薄板电阻点焊熔核内裂纹的愈合方法；.6、构建了铝合金点焊裂纹搅拌摩擦热力耦合修复过程下压力实时采集系统，获得了工艺参数对裂纹愈合效果的影响规律；.7、获得了搅拌摩擦热力耦合修复铝合金点焊裂纹的阻力和驱动力，建立了裂纹修复的能量判据：以摩擦力做功为主的系统能量必须大于裂纹修复所需的结晶晶界能、激活能、扩散能及热能；.8、阐明了搅拌摩擦热力耦合修复铝合金点焊裂纹的机理：扩散不是主要机制，主要通过再结晶和修复结晶实现；.9、建立了基于Johnson-Cook模型理论的铝合金点焊接头搅拌摩擦修复过程的三维热力耦合模型，提出了增大局部接触热导率模拟点焊熔核传热的方法，揭示了修复过程高温区和高应变区的分布及演变规律。.项目成果不仅对从根本上消除高强铝合金在热加工过程中的裂纹及微裂纹缺陷，提高结构的综合机械性能和工作可靠性有重要的理论意义和工程应用价值，同时对发展金属材料的愈合理论与技术具有积极意义。