Al-Zn-Mg-Cu合金包覆淬火残余应力与微观组织及性能的相关性研究

The large size Al-Zn-Mg-Cu aluminum alloys are the key structural material in the modern aviation and aerospace industry. During the aging process, a large amount of dispersion strengthening phases precipitate from the supersaturated solid solution produced during quenching, which leads to the strengthening of the alloys. However, the quenching process generates a great residual stresses in alloys and hence seriously affecting their subsequent machining and final properties. Therefore, this project puts forward a novel cladding quenching method to achieve the reduced quenching residual stresses while maintained properties of aluminum alloys, where an ideal "S-shaped" cooling curve and relaxation surface stresses are obtained through the cladding layer during cladding quenching. In present project, the effects of the cladding thickness on quenching residual stresses and strength, plasticity and conductivity of the aged alloys will be studied. The formation of microstructure, including the types, number, morphology, sizes, distribution and orientation of precipitated phases, as well as the density and distribution of internal dislocations in both of the quenched and aged alloys will be investigated. The interaction of residual stresses and precipitation phases and dislocations and the correlation between macroscopic properties, residual stresses and microstructures will be revealed. The mechanism on the reduced residual stresses and maintained properties by cladding quenching processing will be clarified as well. The purposes of these investigations are to optimize the cladding quenching process conditions and to provide a new type of quenching process and theoretical guidance for the production of high-performance aluminum alloys thick plates and large forgings with high strength, high toughness and low residual stresses.

大尺寸Al-Zn-Mg-Cu合金是现代航空航天工业的关键结构材料，淬火获得过饱和固溶体才能在时效中析出大量弥散相而使合金强化，但同时也会产生较大的残余应力，严重影响其后续机加工和最终性能。为了实现保持铝合金性能的同时能显著降低淬火残余应力，本项目提出一种试图通过包覆层获得一种理想的“S型”冷却曲线和松弛表层应力的包覆淬火新方法。主要研究内容包括：包覆层厚度对合金淬火残余应力及其时效处理后强度、塑性及电导率的影响规律；包覆淬火与时效后合金中析出相的种类、数量、形貌、尺寸、分布和取向等微观组织的形成规律，以及析出相与内部位错密度沿厚度的分布规律；探明残余应力与析出相和位错的相互作用规律，以及宏观性能和残余应力与微观组织之间的相关性，揭示包覆淬火降低合金残余应力并保持其性能的机理，优化包覆淬火工艺条件，为高强、高韧、低残余应力高性能铝合金厚板、大型锻件的生产提供新型淬火方法和相关理论指导。

现代航空航天制造趋势正在向着整体化结构发展，即使用越来越多的复杂整体结构件代替装配件，以达到高强轻质并减少生产制造成本的要求，大尺寸Al-Zn-Mg-Cu 合金材料因其在强度、韧性和耐腐蚀性等各方面优异的综合性能而得到广泛的应用。作为典型析出强化型合金，Al-Zn-Mg-Cu合金为了获得较高的强化效果需在固溶后进行淬火，而淬火过程易产生较大的残余应力，严重影响后续的机加工和最终性能。目前，国内外对Al-Zn-Mg-Cu 合金成分优化设计及调控、多尺度第二相强韧化理论及组织性能调控等方面进行了大量研究，取得了一系列的显著成果，但是有关铝合金残余应力方面的研究相对匮乏，尤其是缺少行之有效的调控或消除残余应力的手段。本项目通过：（1）可降低Al-Zn-Mg-Cu合金淬火残余应力和保持性能的新型包覆淬火工艺研究；（2）Al-Zn-Mg-Cu合金包覆淬火残余应力与时效工艺研究；（3）Al-Zn-Mg-Cu合金包覆淬火残余应力与微观组织及性能的相关性研究；（4）Zn含量对Al-Zn-Mg-Cu合金热变形动态软化行为的影响；（5）铝合金中位错、组织等与宏观性能的相关性研究；（6）不同Zn含量的Al-Zn-Mg-Cu合金的析出演化和强化作用；（7）包覆淬火工艺对复杂截面Al-Zn-Mg-Cu合金件的残余应力及性能的影响研究等。成功提出了一种新的包覆淬火工艺，探究了包覆淬火工艺的应用范围和工艺效果，优化了包覆淬火工艺条件，揭示了包覆淬火工艺的作用机理，研究了残余应力对合金时效过程中析出行为的影响，探明了残余应力和析出相以及宏观性能之间的相关性。项目一定程度上解决了残余应力这一制约国产大尺寸高性能铝合金材料实际应用的棘手问题，为我国大规格高性能铝合金材料制造工艺领域的发展做出了一定的贡献。