Effect of Sc Element on Microstructure,Mechanical Properties and Fatigue Crack Propagation Behavior of Al-Cu-Li Alloys
[Purposes]The microstructure,mechanical properties and fatigue crack propagation of Al-Cu-Li alloy containing Sc element were analyzed.The influence factors of Sc element addition on grain structure,precipitation behavior,mechanical behavior and fatigue crack propagation were summarized,which provided reference for the design of Al-Cu-Li alloy with high comprehensive performance.[Meth-ods]Hardness,room temperature tensile and fatigue crack propagation tests,combined with SEM/EDS,EBSD and TEM characterization,were used to analyze the effect of Sc elements on the microstructure,mechanical properties and fatigue crack propagation behavior of Al-Cu-Li alloys.[Findings]The grain size of Sc-free alloys was larger than that of Sc-containing alloys.The hardness of the Sc-free alloy was 182±2 HV3,which was significantly higher than that of the Sc-containing alloy of 171±2 HV3.The room temperature tensile properties also showed that the strength of the Sc-free alloy was significantly higher than that of the Sc-containing alloy,but the elongation at break of the Sc-containing alloy was higher.At the same number of cyclic loading,the crack length of the Sc-containing alloy was significantly lower than that of the Sc-free alloy,and the FCP rate of the Sc-free alloy was higher than that of the Sc-containing alloy.[Conclusions]The formation of Al3(Sc,Zr)phase in Sc-containing alloys improves sta-bility at high temperatures,increases pinning to grain boundaries,and inhibits grain growth.Both AlCu-FeMn and AlCuSc(W)phases consume Cu elements,which reduces the precipitation of the T1 phase dur-ing the aging process and lowers the strength of the alloys.Compared with Sc-free alloys,cracks mean-der around the W phase formed by Sc-containing alloys,leading to crack deflection in the propagation path,and Sc-containing alloys have a higher dislocation density,which provides a better blockage of crack propagation at high stress-strength factors.