金属固态焊合微观机制的原子尺度模拟研究

Metal could establish solid state bonding under specific physical condistions, such as specific temperature, pressure and plastic deformation. Solid state bonding is responsible for solid state welding methods (such as friction welding, diffusion bonding, cold pressure welding, etc.), crack healing during forge and extrusion using the porthole die. The published researches are focused on experimental studies on the effect of different variables, and theoretical analysis of the solid state bonding process.However, the atomistic mechanism of solid state bonding is still not clear. Studying the atomistic mechanism could provide the theory basis for deeply researching the related processing technologies. In this project, aiming to clarify the micro-mechanism of the the solid state bonding and generate an analytical model for predicting the bonding efficiency, the solid state bonding is to be modeled by using molecular dynamics (MD)simulation, and experiments are also to be carried out. In particular, atomistic simulation is to be used to study the atomistic mechanism of solid state bonding under different physical condistions. The effects of different physical conditions on the solid state bonding are to be obtained. The tensile performance of the solid state joint is to be investigated by the MD simulation. An analytical model for predicting the bonding efficiency is to be generated based on the simulation results and the experimental results. Moreover, the mechanical performances of friction stir welds are to be obtained in order to validate the the bonding efficiency predicting model.

固态焊合是指分离的固态金属在一定的温度、压力、塑性变形等条件下实现紧密接触，并发生冶金结合的过程。金属固态焊合是摩擦焊、扩散焊、冷压焊等固态焊接方法以及锻造过程中内部孔洞愈合和分流焊合挤压过程中共有的基本物理过程。国内外已有研究主要集中在焊合影响因素的实验研究与焊合过程的理论分析方面，然而固态焊合过程原子尺度的微观机制尚不明确。研究其微观机制，为相关加工方法研究提供理论依据，具有重要意义。本课题基于分子动力学模拟，结合实验方法，研究固态焊合微观过程，揭示金属固态焊合过程的微观机制，建立焊合效率的定量预测模型。课题主要开展以下研究：模拟不同物理条件（如温度、压力等）下固态焊合的微观过程，阐明固态焊合的微观机制；结合模拟结果与实验结果，阐明物理条件对接头力学性能的影响规律与机制，建立焊合效率的预测模型；以搅拌摩擦焊为代表，研究不同工艺参数下接头的力学性能，对焊合效率预测模型进行验证。

固态焊合是指在一定的温度、压力等条件下实现固态金属表面间的直接连接，是搅拌摩擦焊等制造技术中共有的基本物理过程。尽管基于固态焊合的制造技术应用广泛，但微观机制尚不明确，这使得相关实际工艺的设计与优化往往缺少理论依据。作为应用基础研究，本项目针对基本物理现象以及实际焊接工艺，均开展了较深入的研究，取得以下三方面进展：（1）通过建立固态焊合过程的原子尺度模拟模型，研究了不同物理条件下固态焊合的物理过程，阐明了固态焊合中材料通过实现原子级紧密接触实现焊合的内在物理机制；（2）建立并验证了界面焊合比例的定量预测模型，定量阐明了固态焊合过程中界面焊合比例与压力、温度、加载时间之间的定量关系，为分析各种复杂物理条件下的固态焊合行为提供了数学方法与科学依据；（3）针对搅拌摩擦焊工艺，定量研究了搅拌摩擦焊接头中宏/微观缺陷的形成机制及其受焊接参数影响的规律，实现了相关接头缺陷的定量预测。本项目的开展进一步揭示了金属固态焊合的微观机制，形成了研究固态焊合过程的新的定量数学方法，有助于对搅拌摩擦焊等实际过程中焊合缺陷的准确理解，为进一步分析各种复杂工艺条件下的固态焊合行为提供了与科学依据与理论基础。