Microstructure, mechanical and fracture properties of friction stir welded 2195 Al-Li alloy joints

IF 5.3 1区工程技术 Q1 ENGINEERING, AEROSPACE Chinese Journal of Aeronautics Pub Date : 2024-01-01 DOI:10.1016/j.cja.2023.10.017

Guangda SUN , Weizhao SUN , Li ZHOU , Sanfeng LUO , Zili ZHANG , Debo LIU , Huiqiang WU

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Abstract

The 8 mm-thick 2195 Al-Li alloy joints were achieved by Friction Stir Welding (FSW). The microstructural evolution, temperature-dependent mechanical properties, and fracture properties were studied. The T₁, δ′/β′ and θ′ precipitates were observed in the Base Metal (BM) and the Heat Affected Zone (HAZ). Most of the precipitates, except for re-precipitated δ′/β′ phases, were dissolved in the Nugget Zone (NZ). The tensile specimens that failed at cryogenic temperatures (–196 °C) had the maximum Ultimate Tensile Strength (UTS), and the fracture surface showed the inter-granular fracture characteristics. Compared to those at room temperature (25 °C), the decreasing tensile properties at high temperature (180 °C) were related to microstructure and strain hardening effects. The NZ presented the optimal fracture toughness, and the Crack Tip Opening Displacement (CTOD) was mutually dominated by microhardness and grain size. Analysis on Fatigue Crack Growth (FCG) rates indicates that the Thermal-Mechanically Affected Zone (TMAZ) exhibited the most superior fatigue resistance performance at stress intensity range below 17 MPa·m^1/2 due to compressive residual stress and the crack closure effect. The fatigue fracture surfaces reveal that the crack propagation zone was characterized by the striations and secondary cracks. Also, inter-granular fracture behavior was responsible for the fastest FCG rates in the NZ.

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摩擦搅拌焊接 2195 Al-Li 合金接头的微观结构、机械性能和断裂性能

通过搅拌摩擦焊（FSW）实现了 8 毫米厚的 2195 Al-Li 合金接头。研究了微观结构演变、随温度变化的力学性能和断裂性能。在基体金属（BM）和热影响区（HAZ）中观察到了 T1、δ′/β′ 和 θ′析出物。除再沉淀的 δ′/β′ 相外，大部分沉淀物都溶解在金块区 (NZ) 中。在低温（-196 °C）下失效的拉伸试样具有最大极限拉伸强度（UTS），断裂面显示出晶粒间断裂特征。与室温（25 ℃）下相比，高温（180 ℃）下拉伸性能的下降与微观结构和应变硬化效应有关。NZ 具有最佳的断裂韧性，裂纹尖端张开位移（CTOD）受微硬度和晶粒尺寸的共同影响。疲劳裂纹生长（FCG）率分析表明，由于压缩残余应力和裂纹闭合效应，热机械影响区（TMAZ）在应力强度低于 17 MPa-m1/2 时表现出最优异的抗疲劳性能。疲劳断裂表面显示，裂纹扩展区的特征是条纹和次生裂纹。此外，粒间断裂行为也是造成 NZ FCG 速度最快的原因。

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来源期刊

Chinese Journal of Aeronautics 工程技术-工程：宇航

CiteScore

10.00

自引率

17.50%

发文量

3080

审稿时长

55 days

期刊介绍： Chinese Journal of Aeronautics (CJA) is an open access, peer-reviewed international journal covering all aspects of aerospace engineering. The Journal reports the scientific and technological achievements and frontiers in aeronautic engineering and astronautic engineering, in both theory and practice, such as theoretical research articles, experiment ones, research notes, comprehensive reviews, technological briefs and other reports on the latest developments and everything related to the fields of aeronautics and astronautics, as well as those ground equipment concerned.