基于FSP多场耦合的高强铝合金焊缝表面超细晶化控制及腐蚀行为研究

At present, FSW Joints for high-strength aluminium alloys as an important structure in the aircraft was used as important structure in the aircraft. However, Since the corrosion resistance of weld surface was poor，its application has been limited.When the grain refinement is perform on the surface of aluminium alloys with an inactivation, the surface corrosion resistance can be improved. In this project, the weld surface of 2024 aluminium alloys adding low cost Al-based amorphous as a refining factor can obtain the stable ultra-fine grain structure under the multi-field coupling of FSP. And the corrosion resistance on the weld surface will be improved via the control of crystallization for Al-based amorphous. The quantitative and qualitative analysis for the ultra-fine structure in the weld surface will be performed. Moreover, the microstructure characteristics in the interface zone between the ultra-fine layer and the internal weld are also studied. The influence of content, crystallization behavior and microstructure evolution on the ultra-fine grain and corrosion resistance in weld surface will be revealed by means of analysis and study. The inner link between the ultra-fine grain formed and some key factors, such as the processing condition of multi-field coupling, the characteristics of amorphous alloys can be searched. As a result, the mechanics of ultra-fine grain formed of the weld surface and corrosion resistance under the multi-field coupling of FSP will be studied and discussed. This study will provide a novel research approach for improving the corrosion resistance of weld surface of high-strength aluminium alloys, and this study will have important theoretical meaning and research value for expanding their applications of high-strength aluminium and amorphous alloys.

高强铝合金搅拌摩擦焊接头已被应用于航空航天领域，但其焊缝表面的抗腐蚀性较差，直接影响使用性能，而对具有钝化性质的铝合金表面进行晶粒细化处理，有助于提高抗腐蚀性。本项目提出基于多场耦合的搅拌摩擦加工技术，辅助铝基非晶为细化因子，诱导2024高强铝合金搅拌摩擦焊缝表面形成稳定的超细晶化层，通过控制非晶合金的晶化，提高表面抗腐蚀性。对表面超细晶化层进行定量、定性分析，研究超细晶化层及其与焊缝之间界面附近的微观组织结构，揭示非晶合金含量、晶化行为及组织结构演变对焊缝表面超细晶化及抗腐蚀性的影响规律，寻求搅拌摩擦-多场耦合、细化因子特性与焊缝表面超细晶化形成的内在联系及叠加效应，探讨焊缝表面超细晶化及抗腐蚀机理。该研究将为提高高强铝合金焊缝表面抗腐蚀性提供一种新颖的研究思路，对拓展高强铝合金及非晶合金的应用具有重要的理论意义与研究价值。

高强铝合金搅拌摩擦焊接头已被应用于航空航天领域，但其焊缝表面的抗腐蚀性较差，直接影响使用性能，而对具有钝化性质的铝合金表面进行晶粒细化处理，有助于提高抗腐蚀性。本项目主要开展了焊缝表面FSP加工细化因子及工艺性研究、焊缝及加工表面微观组织结构特征及影响因素和焊缝表面抗腐蚀性能及影响机理。研究表明，经过搅拌摩擦加工后焊缝表面区域的抗拉强度并非存在线性的增长关系，随着转速的提高，抗拉强度先增加后降低；添加辅助非晶材料后表面呈现多层“sandwich”结构，并在“sandwich”结合区存在少量的非晶晶化La-Al系化合物。而由于各种强化或弱化析出相的存在或消失，严重影响焊缝表面及近表面的组织结构转变与性能，在近焊缝表面区存在Al-Cu-Mg系自生成非晶组织和局部微米尺度范围的纳米组织。搅拌摩擦加工后，添加辅助非晶材料的焊缝表面的自腐蚀电流icorr、腐蚀电流密度及腐蚀电位均高于未添加辅助非晶材料的区域，且辅助非晶材料并非完全进行了晶化或组织转变，而是部分的独立存在于超细晶化组织与基体组织之间。同时，未完全晶化的非晶材料与基体组成的表面加工层的热稳定性要高于母材表面，即热稳定性较好的二次加工组织利于其抗腐蚀性能的提高。此外，不同转速条件下，进行搅拌摩擦加工后焊缝表面加工区的腐蚀性能存在一定规律性，随搅拌摩擦转速的提高，自腐蚀电流密度将逐渐提高，并且经过二次FSP加工后其组织得到更加显著的细化，原有表面疑似细孔的结构完全的连续化。通过该项目的研究，在实现了铝合金搅拌摩擦焊焊缝表面二次FSP强化加工基础上，揭示了焊缝加工处理后其耐腐蚀性提高与基体材料组织转变之间的关系，为后续进一步优化工艺及其推广应用提供重要的研究基础。同时该项目将材料热分析方法用于该研究中，为阐述其微观组织转变机理及其影响腐蚀性能提供了良好的研究途径。