Al3(Sc1-xZrx)纳米粒子提高航天铝锌镁合金FSW接头SCC抗力的机理研究

With the advent of low-latitude coastal launch mission, the stress corrosion cracking (SCC) problem of the friction stir welded (FSW) joints of aerospace aluminum alloys demands prompt solution. The applicants have found that Al3(Sc1-xZrx) nano-particles can improve the SCC resistance of Al-Zn-Mg alloy FSW joints, but the mechanism is unclear. SCC only occurs when there is a "window corresponding" condition between the materials and corrosion environment. Therefore, this research will commence with searching for "window corresponding" critical microstructure. The investigation is as follows. According to the microstructure, micro-area potential distributions and SCC behaviour of friction stir welded joints of aerospace Al-Zn-Mg and Al-Zn-Mg-Sc-Zr alloys, the key microstructure for determining SCC of the joint will be distinct. Based on the existing form of Al3(Sc1-xZrx) particles in the joint and the interaction between nano-particles and grain boundary, dislocation and vacancy under the welding thermal-mechanical cycle, the constitutive relationship model between nano-particles, key microstructure and SCC behaviour will be established. Furthermore, the mechanism for improving SCC resistance by particles will be revealed. Consequently, this project offers a new idea for SCC control of welded products, and is of great significance in the highly reliable application for spacecraft and the sustainable development of aerospace project.

随着我国低纬度滨海发射任务的到来，航天铝合金搅拌摩擦焊（FSW）接头的应力腐蚀开裂（SCC)问题亟待解决。申请人发现，Al3(Sc1-xZrx)纳米粒子可提高铝锌镁合金FSW接头SCC抗力，但机理不明。SCC的发生需存在一个材料与腐蚀环境“窗口对应”条件，本项目从寻找接头与SCC“窗口对应”的关键显微组织着手，进行以下研究：以航天用Al-Zn-Mg和Al-Zn-Mg-Sc-Zr合金FSW接头为研究对象，根据接头显微组织、微区电位分布和SCC行为特性，明晰影响接头SCC的关键显微组织; 查清Al3(Sc1-xZrx)在接头中的存在形态，掌握纳米粒子在焊接热力循环下与晶界、位错和空位的定量交互作用规律，建立纳米粒子-关键显微组织-SCC行为三者构性关系模型，揭示粒子提高接头SCC抗力机理。本项目的顺利开展，为焊件SCC控制提供了一种全新思路，对航天器高可靠使用和航天事业可持续发展具有重要意义。

随着我国低纬度滨海发射任务的到来，航天铝合金搅拌摩擦焊（FSW）接头的应力腐蚀开裂（SCC)问题亟待解决。针对Al3(Sc1-xZrx)纳米粒子可提高铝锌镁合金FSW接头SCC抗力，但机理不明这一科学问题，本项目按照研究计划，设计制备了航天用Al-Zn-Mg和Al-Zn-Mg-Sc-Zr合金板材，并实现了板材的高强度FSW焊接；以接头为研究对象，结合现代显微分析方法、慢应变速率拉伸实验和电化学测试，明晰了影响接头SCC的关键显微组织，查清了Al3(Sc1-xZrx)在FSW接头中的存在形态，掌握了纳米粒子在热力变形下微结构的演变规律，揭示了粒子提高接头SCC抗力机理。结果表明：在整个焊接接头中，Al3(Sc1-xZrx)纳米粒子与基体保持共格关系，可有效抑制焊接过程中的再结晶和晶粒长大，细化晶粒促进均匀滑移，降低接头不同微区电化学差异，有效抑制PFZs的形成，从而提高接头SCC抗力。本项目的顺利开展，为焊件SCC控制提供了一种全新思路，对航天器高可靠使用和航天事业可持续发展具有重要意义。