搅拌摩擦焊周期性响应行为的热力耦合机理研究

The periodic response behavior of friction stir welding (FSW) is the unique personality characteristics compared with other friction welding method, which causes by the constant speed (travel speed) driving severe plastic deformation system. However, the opinion that this periodic response behavior is the visco-plastic metal moving with the periodic movement of the stir pin, not only is indiscreet but also impedes further understanding the nature of plastic flow and mechanism of weld forming mechanism of friction stir welding. This proposal suggests the method of combining dynamics and thermodynamics to analyze the intrinsic thermal mechanical coupling mechanism of FSW periodic response behavior. Firstly, based on the homogeneous and heterogeneous friction experiments, the thermal mechanical coupling characteristics of the severe plastic deformation system are established. Secondly, according to physical simulation of constant speed driven severe plastic deformation system of FSW, the response behavior and microstructure characteristics of the speed driven deformation material is obtained, and the formation mechanism of the periodic response behavior during FSW processing. Based on the PLC effect method and the nonlinear mechanics, the unstability criterion of the viscoplastic metal in the front of the stir pin is established. Finally, based on the basis of dynamics and non-equilibrium thermodynamics, the analytical model of the temporal and spatial distribution of the severe plastic deformation system and the periodic response behavior produced by FSW is proposed. The research will enrich the fundamentals of process theory on friction stir welding and support the further study on joint reliability.

周期性响应行为是搅拌摩擦焊(FSW)与其它摩擦焊方法相比所独有的个性基本特征，其形成原因是恒速（前进速度）驱动摩擦大变形体系导致，目前却将此行为归结为粘塑性金属随搅拌针周期性运动的结果，严重阻碍了对搅拌摩擦焊形成机理的深入认识。本研究提出动力学与热力学相结合的方法，分析FSW周期性响应行为的热力耦合机理问题。首先，基于同质和异质摩擦实验，建立摩擦大变形体系的热力耦合表征。其次，通过物理模拟恒速驱动摩擦大变形体系的方法，获取材料在恒速驱动下力学响应行为及组织特点的变化规律，分析FSW周期性响应行为的形成机理。通过借鉴PLC效应研究方法和非线性动力学，建立搅拌针前沿粘塑性金属的失稳判据。最后，在上述研究基础上，分别从动力学与非平衡热力学出发，研究FSW周期性响应行为与其摩擦大变形体系形成与演变的时、空统一性问题。研究成果将为搅拌摩擦焊制造供工艺理论基础，并为接头可靠性研究提供理论支撑。

定压摩擦条件下同质或异质组配摩擦实验表明摩擦大变形体的形成必须达到粘塑性流动阶段。旋转速度对峰值摩擦系数和到达峰值摩擦系数时间的响应更加显著，与此相反的是旋转速度不是影响准稳定阶段摩擦系数的关键因素对准稳定阶段摩擦系数的影响不显著。通过流体控制方程基于以上实验基础，并结合流体控制方程、材料本构方程建立了定压条件下同质组配摩擦大变形体粘塑性流动阶段峰值温度与稳态焊接功率的数理模型，并利用采用同质铝合金组配铝合金管2024/2024摩擦实验结果进行验证，证明说明了该模型具有一定的准确性和可靠性。.基于上述摩擦大变形体粘塑性流动阶段表征参量的数理模型，并以峰值温度及FSW个性特征以塑性变形领域唯象的Campbell稳定性判据为边界条件，为边界条件，结合基于合理假设、反双曲正弦本构方程及流体动力学作为基本控制方程，以应变速率敏感系数为中间变量，建立了FSW个性特征的摩擦大变形体核区峰值温度与FSW工艺参数之间的数理关系，，通过对比文献和实验结果与的峰值温度和解析模型的计算结果对比表明，两者的误差在2%-5%，证明FSW摩擦大变形体核区峰值温度数理模型具有一定准确性的普适性和可靠性准确性。.基于在不同工艺参数条件下的进行AA5083铝合金同质FSW对接实验结果，利用量纲分析方法建立FSW摩擦大变形体接头抗拉强度数理模型，并通过实验验证模型的准确性，误差在5%以内证明了模型的正确性，结果证明最优的加工工艺窗口所对应的焊接热输入值在ω/v=4-5 rev/mm之间，结合FSW摩擦大变形体峰值温度数理模型分析了焊接缺陷产生的原因，证明了旨在通过该数理模型指导工艺参数的选取和优化的合理性。.通过对搅拌摩擦焊过程中扭矩、位移、温度、挠度等物理参量的测量及焊后组织的分析，揭示了搅拌摩擦焊过程中的周期性特征。基于周期性特征，实现了搅拌摩擦焊周期性形成过程的运动学、粘塑性力学及温度场的解析分析，建立了搅拌摩擦焊工艺参数优化的数理模型。基于上述对于金属材料流动行为的研究，提出了一种基于扭矩周期性变化特征的焊缝孔洞型缺陷动态检测的方法。