电流对AlZnMgCu合金时效空位和团簇演化的多尺度作用效应与机制

The vacancies and solute at the early ageing stage is the key issue of controlling the process of ageing precipitation. The melting of aluminum and aluminum alloy by Joule heating effect through connecting electric current directly was resolved. With the combination of experimental researches and theoretical calculations, at the bases on the single atomic scale, multi-atomic scale and macro-behavior and micro-behavior of material, effects of the current type(D.C. current and A.C. current), current density, the natural ageing on the evolutions of size, number, and distribution of microstructures (vacancies, solute clusters, GP zone and incoherent phase) during the isothermal ageing process is to be studied, the binding style of vacancies with the solute clusters, GP zone and incoherent phase is to be investigated, the influences of the electric current type and the current density on the microstructure is to be analyzed, the mechanism of the effects of electric current on the microstructural evolutions is to be clarified, the relationship between the microstructure and properties of Al-Zn-Mg-Cu alloy is to be determined, the prediction system between the positron lifetime and the mechanical properties is to be established by the characterization of the microstructure by positron lifetime, the technical proposals to controlling the ageing precipitation by the application of the electric current are to be provided. The research results are expected to enrich the electromagnetic theory of materials, and provide the theoretical and technical supports for developing heat treatment replaced of multi-stage ageing of large aircraft used Al-Zn-Mg-Cu alloy with high strength, high toughness and high corrosion resistance.

时效早期的空位和溶质团簇是控制时效析出的核心问题。在解决了直接通电流因剧烈的焦耳热效应引起Al及Al合金熔化的问题后，本申请采用实验研究和理论计算分析相结合的方法，在单原子尺度、多原子尺度和材料宏、微观行为基础上，研究电流类型(直流电和交流电)、电流密度、自然时效对等温时效中微观组织(空位、溶质团簇、GP区和非共格相的尺寸、数量和分布)的演化的影响，考察空位与溶质团簇、GP区和非共格相的结合方式，分析电流类型和电流密度对微观组织的影响规律，阐明电流对时效析出动力学影响的作用机制，确定合金微观组织与宏观性能的关系，通过正电子湮没技术对微观组织的表征而构建合金的正电子寿命与宏观性能间的预报系统，提出利用电流控制时效析出的技术思路。研究成果可丰富电磁材料学理论，为开发可替代多级时效的大飞机用高强、高韧和高耐蚀性的Al-Zn-Mg-Cu合金的热处理制度提供理论与技术支持。

本项目研究了直流电或交流电以及电流强度对时效强化铝合金单级时效和双级时效过程中微观组织(GP区和时效强化相的尺寸、数量)和性能的影响。在时效过程中施加电流场可以在提高或不降低强度的前提下，明显改善合金的塑性和耐蚀性，并可以显著缩短合金到达峰值时效的时间，且直流电对合金性能的有益效应要大于交流电。7B04合金具有最佳综合性能的电流热处理制度为120℃/100A/12h(T6态120℃/12h)。与T6态相比，电流场时效合金中强化相GP区和η′相的溶解峰的热焓值、平均尺寸和面积分数均增加；随着电流强度的增大，热焓值、平均尺寸和面积分数越大。施加电流场固溶寿命谱中的I2要高于常规固溶，且施加直流电更加明显。表明电流场的施加，增大了淬火后的空位浓度进而促进第二相的析出。