Microstructure Characteristic and Fatigue Damage Behaviors of 2060 Al-Li Alloy Thin Plate

2060铝锂合金薄板组织特征及疲劳损伤行为

¹ Beijing Institute of Aeronautical Materials, Beijing 100095, China
² Beijing Engineering Research Center of Advanced Aluminum Alloys and Applications, Beijing 100095, China
³ Key Lab of Electromagnetic Processing of Materials, Northeastern university, Shenyang 110819, China

Received: 9 April 2019

Abstract

The microstructure characteristic, fatigue damage behaviours and evolution of microstructure during the fatigue testing of 2060 Al-Li alloy thin plate were studied by fatigue tester equipped with in-situ observation device, OM, EBSD, SEM and TEM. The results show that recrystallized grains with irregularity shape and large size are observed, the Goss and Cube texture are the mainly types, abundant of T₁ with size of 50~60nm are found in grains. During axial loaded fatigue testing, a crack initiates from the edge of sample and extend into grain along the direction with maximum Schmid factor. When the crack reaches and crosses the first grain boundary, the extending direction deflects from 45° degree to perpendicular with loading direction, and propagates along this direction till the sample quickly fracture. A large size deformation region contains numerous slip strips around the crack tip during the initiation and extending process is observed. The dislocations cut across the T₁ precipitates located in grains during deformation, and release the stress concentration on the crack tip. The fatigue crack extends across the grains with serrated shape can result from the big orientation difference of grains and easy screwed T₁ precipitates.

摘要

通过带有原位观察设备的疲劳试验机、金相显微镜、EBSD、SEM以及TEM等设备对进口2060-T8E30铝锂合金薄板的组织特征、疲劳损伤行为以及疲劳试验过程中微观组织的演变过程进行了系统研究。结果表明，2060铝锂合金薄板为完全再结晶的块状嵌套组织，织构类型以立方织构和高斯织构为主，晶内析出相主要为T₁相，长度在50~60 nm左右；轴向加载疲劳试验时，裂纹在试样边部缺口附近晶粒中沿最大Schmid因子方向萌生并向晶内扩展，在到达并穿过第一个晶界后裂纹发生偏折，变为垂直于加载方向扩展，继续扩展时，裂纹遇到其他晶界后发生小的偏折，但基本方向不变，直至最终发生瞬断。裂纹萌生和扩展过程中，裂纹尖端出现了较大范围的塑性变形区，该区域中T₁析出相被位错切过，降低了尖端的应力集中。合金中较大的晶粒取向差以及小尺寸可被位错切过的T₁析出相，是疲劳裂纹呈"锯齿"状穿晶扩展并获得良好耐损伤性能的主要原因。