蜻蜓翅膀结构的镁合金焊接接头构筑及疲劳特性研究

Magnesium alloy welded joint is the weak line of fatigue break which restricts the widespread application of magnesium alloy welded structural parts. Dragonfly wing, which is composed of vein and patagium, has favorable fatigue resistance, and it will provide a new idea to improve the fatigue resistance of magnesium alloy welded joint. According to the morphologies of dragonfly wing, welded-seam, HAZ and welded-seam + HAZ are treated by laser beam + ultrasonic peening, respectively. The effect of the morphologies of dragonfly wing on fatigue failure of magnesium alloy welded joint by fatigue test and crack propagation rate, and bionic preparation method will be established. Grain structural (size and shape), second phase (size, shape and distribution) and the matching degree of soft and hard of welded-seam and HAZ treated by laser beam + ultrasonic peening are studied. The influence mechanism of microstructure and the structural of soft and hard on the inhibition of crack initiation and propagation of magnesium alloy welded joint will be revealed. Research results will provide scientific basis for improving the service-life and reliability of magnesium alloy welded structural parts and has important theoretical and practical significance.

镁合金焊接接头是疲劳断裂的薄弱环节制约着镁合金焊接结构件的广泛应用。蜻蜓翅膀是由翅脉和翅膜组成的软硬相间结构具有良好的抗疲劳特性，为改善镁合金焊接接头疲劳性能提供了新的思路。本项目采用激光束+超声冲击复合处理分别在焊缝、热影响区及焊缝+热影响区表面构筑蜻蜓翅膀体表的不同脉络形貌，通过疲劳实验及疲劳裂纹扩展实验明确不同脉络形貌在镁合金焊接接头疲劳失效过程中的作用规律，建立改善镁合金焊接接头疲劳性能的仿生制备方法，研究激光束+超声冲击复合处理对焊缝和热影响区的晶粒结构（尺寸与形状）及第二相特征（形状、尺寸及分布）的影响规律，分析复合处理区域与基体间的软硬匹配程度，揭示微观组织及软硬相间结构抑制镁合金焊接接头疲劳裂纹萌生与扩展的影响机理。研究成果将为提高镁合金焊接结构件的服役寿命和可靠性提供科学依据具有重要的理论和实际意义。

镁合金部件是现代交通运载装备轻量化、节能化和绿色化的重要发展方向，但是镁合金焊接接头疲劳性能是为制约镁合金在高端装备中广泛应用的重要“瓶颈”。本项目以具有软硬相间结构的蜻蜓翅膀为仿生原型，对镁合金焊接接头进行仿生设计；研究揭示了镁合金焊接接头经激光及激光+超声冲击复合处理后微观组织演化规律；研究了不同仿生脉络形貌对疲劳性能的影响规律，高周疲劳试验和疲劳裂纹扩展试验表明，具有不同仿生结构的焊接接头的疲劳强度和疲劳裂纹扩展门槛值较原始态焊接接头有不同幅度的提高，在10000000循环周次下仿生处理后焊接接头疲劳强度提高了17.6%-206.9%，仿生处理后焊接接头焊缝和热影响区疲劳裂纹扩展门槛值分别提高了47.7%-85.6%和41.2%-63.4%，建立了改善镁合金焊接接头疲劳性能的仿生加工技术；对比分析了疲劳试验前后仿生处理焊接接头微观组织变化情况，阐明了晶粒尺寸与孪晶对焊接接头疲劳行为的影响机制；研究了仿生处理焊接接头疲劳断裂特性，给出了软硬匹配对焊接接头断裂行为的作用规律；通过上述研究，揭示了具有仿生结构的镁合金焊接接头抗疲劳裂纹萌生和扩展机理。项目研究成果拓展了工程仿生的研究领域，促进了不同学科间的交叉融合；为改善焊接结构件的服役寿命和可靠性提供了理论基础和实践基础。