铝/钢强形变诱导搅拌摩擦扩散焊界面微区调控机理研究

Assembling aluminium/steel dissimilar materials within integrated structures is nowadays a stringent requirement related to lightweight structures and improved performance for various industrial fields such as transportation, shipbuilding and aerospace. Based on the major challenge due to poor weldability of aluminium to steel, complex interfacial reaction and controlling of intermetallic compounds (IMC), the promising technique of severe deformation inducing friction stir diffusion bonding was proposed with the behavior of high-speed inter-diffusion induced by deformation. The design rules of tools were made according to the requirement of heat input and deformation. The high-speed diffusion mechanism induced by severe deformation was investigated. The atomic diffusion and growing model of interface IMC was established coupling with active energy, reaction temperature and time. The deformation-induced nucleation, the growth kinetics and the evolution of undesirable and brittle IMC were declared. The formation of tough plastic Fe-rich IMC and amorphous structure near the interface due to the mechanical alloying were studied during severe plastic deformation. The interface controlling theory was clarified at the macro-micro-nano multiscale to explore the morphology and distribution of IMC induced by severe plastic deformation. The relationship between interfacial micro-mechanical behavior and joints macro-bearing characteristics was established. The project aims to provide the fundamental theory and effective strategy to the future applications of lightweight structures of aluminium to steel dissimilar material joints. The theory development of diffusion induced by plastic deformation is also the point of interest to investigate the mechanism of other solid state bonding procedures which base on severe plastic deformation and the flow of interfacial materials.

基于铝/钢异种材料结构件轻量化设计在车辆、船舶、航天航空等领域的迫切需求，针对铝/钢异种材料可焊性差、界面反应复杂、金属间化合物难控制等问题，本项目将结合形变诱导快扩散行为，探索强形变诱导搅拌摩擦扩散焊新方法。基于热源和形变调控，提出搅拌摩擦扩散焊搭接焊具的设计准则。解析强形变诱导作用下界面元素快扩散机制，建立界面金属间化合物厚度与扩散激活能、反应温度和时间的扩散数理模型，明晰金属间化合物的形变催化形核、生长机制和演化规律，以及形成塑性富铁金属间化合物的可能性和机械冶金生成非晶层的成因和条件。阐明界面宏微纳观多尺度调控原理，揭示强形变诱导作用下金属间化合物存在形态及分布规律，建立界面微区力学行为和接头宏观承载特性的关联。该技术将为铝/钢异种材料轻量化设计的应用奠定基础和提供设计依据，同时形变诱导扩散机理的明晰对以界面材料高塑性流变为基础的固相连接机制的揭示具有借鉴意义。

基于铝/钢异种材料结构件轻量化设计在车辆、船舶、航天航空等领域的迫切需求，针对铝/钢搭接搅拌摩擦焊（Friction stir welding, FSW）存在可焊性差、焊具易磨损、界面金属间化合物难控制等问题，选取6082-T6铝合金和QSTE340TM细晶粒结构钢为研究对象，利用FSW强形变诱导快扩散作用，开发出了形变诱导FSW新技术和新型焊具。采用试验研究、理论分析和数理模型建立有机结合的方法，围绕强形变诱导作用下元素快扩散机制、界面层控制、微观结构与宏观接头承载特性关联、接头可靠性等开展了研究。新型焊具采用轴肩和搅拌针分体式结构设计，焊具的可加工性和适应性提高，通过引入端部膨大呈内凹式且带有周向三缺口的搅拌针结构，使得界面塑性材料流动性增强、并赋予动静结合双流动模式。研究表明搭接FSW接头界面有效搭接宽度显著增大，钩状结构得到了减弱或者消除，并揭示了界面处材料流动和钩状结构消除的机制，避免了搅拌针和底部钢板的直接接触，有效提升了焊具使役寿命。研究了焊接参数对铝/钢搭接FSW界面宏观成形和缺陷的影响规律，建立了工艺优化窗口。在700和900r/min的转速下，随着焊接速度的提高，搭接界面处的金属间化合物和钢细晶粒层组成的叠层结构逐渐消失，界面由锯齿状向平直状逐步转变。研究了铝/钢搭接FSW接头界面组织与承载性能的关联性。当转速为700r/min时，焊接速度的优化区间为50-250mm/min，随着转速增加到900r/min，焊接速度的优化区间范围降为50-200mm/min，进一步增加转速至1200r/min时，发现焊接速度的优化区间进一步变窄，在焊接速度50mm/min的参数附近呈现出最优的剪切性能，线承载达到483.3N/mm。表征了界面处快扩散行为，界面区主要由颗粒复合结构、叠层结构和金属间化合物层构成，且部分区域存在非晶态的原子组态。FSW施加的搅拌和剪切作用引起的局部应力和应变所导致的铝合金晶粒的细化和产生的高浓度的位错，为Fe元素的扩散提供更多的路径及为Fe4Al13晶粒的形核提供形核点，揭示了快扩散现象的本质。