Effect of thermal exposure on the microstructure and properties of an Al-Cu-Li alloy
As a promising structural material in the aerospace industry,the long-term thermal stability of Al-Cu-Li alloys plays an important role in practical applications.In this study,the T85-treated Al-Cu-Li alloy subjected to thermal exposure at a range of temperatures(100～300℃)for 500 h,is evalu-ated by Vickers hardness,electrical conductivity and tensile tests.The microstructure evolution at dif-ferent heat exposure temperatures is analyzed by a combination of scanning electron microscopy(SEM)and transmission electron microscopy(TEM).The results show that excellent thermal stabil-ity in strength is obtained below 150℃,which can be related to the increasing diameter and number density of the T1(Al2CuLi)phase.In the 150～200℃ window,the T1 phase is gradually replaced by coarse θ'-Al2Cu and S-Al2CuMg with increasing temperature.Simultaneously,discontinuous grain boundary precipitates(GBPs)and soft precipitation-free zones(PFZs)lead to intergranular ductile fracture dominance,exhibiting mixed ductile and brittle fracture.At temperatures above 250℃,the T1 phase is completely dissolved and coarse T2(Al6Cu(Li,Mg)3)and C phases are formed.This leads to a dramatic decrease in the strength,while elongation and conductivity show an opposite trend.
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