一种新型Al-Zn-Mg-Cu合金大尺寸变截面盘类件等温压扭成形工艺及应力腐蚀控性机理研究

Heavy-gauge discs of Al-Zn-Mg-Cu alloy with variable cross-section are widely used in aerospace and nuke industry. The present forming processes cannot satisfy the demands of both high strength and low stress-corrosion sensibility. High-pressure torsion process belonging to sever plastic deformation can remarkably refine the grains, leading to the dissolving of multi-alloy phase and the emergence of supersaturated solid solution. The process presents the possibility for improving the properties of the alloy via subsequent aging treatments. In this study, the discs (>Φ50mm) of novel Al-Zn-Mg-Cu alloy (12 wt.% Zn) are processed by high pressure torsion. Based on the theories of anodic dissolution and hydrogen-induced cracking, the influences of both grain refinement and multi-phase dissolving on the composition, size and distribution of the dispersed phase will be analyzed from the perspectives of dynamics (diffusion) , electrochemistry and the mechanism of grain-refinement, working and aging strengthening. According to these principles, the strengths and the resistances against stress-corrosion of all the distinguished sections of the disc, like the bottom and the corner at the root, are tested in order to control the over-all properties of the disc. This study will improve the theory of stress-corrosion of Al alloy, widen the industrial application of pressure torsion and develop novel ideas and methods for fabricating high-performance Al alloy parts, which has scientific value.

Al-Zn-Mg-Cu合金大尺寸变截面盘类件广泛应用于航空航天、核工业等尖端领域，现有成形工艺无法兼顾高强度和低应力腐蚀敏感性的服役要求。压扭大塑性变形工艺在显著细化晶粒的同时可诱导多元合金相回溶形成过饱和固溶体，为后续时效处理充分挖掘合金性能提供可能。本研究对一种新型Al-Zn-Mg-Cu合金（12 wt.% Zn）盘类件（>Φ50mm）开展压扭成形工艺实验。基于阳极溶解和氢致破裂理论，从动力学（扩散）和电化学相关理论以及细晶强化、形变强化、时效强化机制出发，深入分析晶粒细化和多元合金相回溶对后续时效处理弥散相成分、尺寸及分布的影响，测试各特征部位（盘面及根部圆角过渡区）强度和抗应力腐蚀性能，揭示其机理，以期达到该类件高强度和良好抗应力腐蚀性能的控性目标。本研究完善了超高强铝合金抗应力腐蚀理论、拓展了压扭工艺的工业化应用，为成形高性能铝合金零件开辟新思路和研究方法，具有重要的科研价值。

高强低应力腐蚀Al-Zn-Mg-Cu合金大尺寸变截面盘类件是航空航天、核工业领域的重大需求，但现有喷射成形及反挤压工艺难以实现高Zn含量该类合金强度、韧性以及抗应力腐蚀性能的最佳匹配。本项目创新性的提出压扭大塑性变形-多级形变热处理双控制造工艺，并围绕压扭变形-热处理过程晶粒细化、多元合金相回溶-析出规律及其对铝合金强度、塑性和应力腐蚀行为的影响机理这一科学问题，在Al-Zn-Mg-Cu合金压扭成形微观组织及性能表征、全过程仿真、工艺实验方面开展深入研究。. 本研究探明了铸态及轧制态Al-Zn-Mg-Cu合金压扭大塑性变形过程晶粒及第二相形貌及取向分布的演变行为及其多机制控制下的晶粒细化、第二相动态回溶-析出微观机理。结果表明Al-Zn-Mg-Cu合金压扭变形过程中变形机制包括晶粒内部的多系滑移、晶粒剪切破碎和位向转动，以及应力诱导的再结晶，主要强化相MgZn2在压扭过程变形热累积和非平衡界面处强应力场作用下发生回溶；随应变进一步增大，界面浓度梯度差和Gibbs-Thompson效应诱发其再析出和长大。通过电化学腐蚀实验和慢应变速率拉伸实验，发现由于晶界处粗大MgZn2相在压扭成形过程中破碎细化且整体含量降低，导致材料腐蚀电流密度减小和腐蚀敏感性的降低。针对新型Al-Zn-Mg-Cu合金盘类件（>Φ50mm）开发了压扭成形-多级形变热处理工艺，通过在显著细化晶粒的同时诱导多元合金相回溶形成过饱和固溶体，并利用形变相变交互作用在后续时效处理过程中定向析出非共格合金相，实现了盘类件强塑性极限的突破及综合服役性能的稳定提升（强度>700MPa，延伸率>5%），本研究完善了超高强铝合金抗应力腐蚀理论、拓展了压扭工艺的工业化应用，为成形高性能铝合金零件开辟新思路和研究方法。. 在项目支持下共发表论文33篇，SCI论文9篇；申请发明专利6项，授权3项。