5A90铝锂合金的蠕变时效行为及机理

Creep Aging Behavior and Mechanism of 5A90 Al-Li Alloy

研究了在不同时效温度和应力水平的影响下,5A90铝锂合金的蠕变时效行为和微观组织及力学性能演变规律和机理。实验采取先加载后加热的方法,即考虑了蠕变时效非等温阶段。结果表明:在恒定外加应力175MPa下,加热至100、130和160℃时的非等温蠕变应变分别为0.026%、0.036%和0.069%;160℃下等温阶段保持18 h后的蠕变应变达到1.207%,远大于130℃下的0.079%和100℃下的0.039%;蠕变应变速率随温度升高而增加;由于蠕变损伤,160℃下出现蠕变第3阶段。研究了130℃下不同应力水平对微观组织和力学性能演变的影响,发现应力为175 MPa时,非等温蠕变变形很明显,但在125和150 MPa下加热至120℃之前不会发生蠕变,并且等温蠕变应变随应力增大而增加;较高的应力可以促进δ′(Al3Li)、S(Al2MgLi)相的析出和长大;在蠕变时效初期,应力越大,位错密度越小,而在蠕变时效的后期则相反;与125和150 MPa相比,合金在175 MPa下蠕变时效初期表现出最低的强度和最好的塑性,而在蠕变时效后期则相反,这归因于位错强化和δ′相强化之间的协同作用。

The evolution principles and mechanisms of the creep aging behavior,microstructure,and mechanical properties of 5A90 Al-Li alloy under the effects of different aging temperatures and stress levels are studied.The nonisothermal stage in creep aging is considered under the thermal-mechanical loading sequence of loading prior to heating.The results show that,under the constant applied stress of 175 MPa,the non-isothermal creep strains when heated to 100℃,130℃ and 160℃ are 0.026%,0.036%and 0.069%,respectively.The creep strain reaches 1.207%after the isothermal stage is maintained for 18 h at 160℃,which is much higher than 0.079%at 130℃ and 0.039%at 100℃.The creep strain rate increases with the increase in the temperature.Due to creep damage,the tertiary creep stage occurs at 160℃.The effects of different stress levels on the microstructure and mechanical property evolutions at 130℃ are studied.It is found that the non-isothermal creep deformation is obvious under 175 MPa.However,no creep will occur before heating to 120℃ under 125 MPa and 150 MPa.Moreover,the isothermal creep strain increases with the increase in the stress.Higher stress can promote the precipitation and growth of theδ′(Al3Li)and S(Al2MgLi)phases.In the early stage of creep aging,the larger the stress is,the smaller the dislocation density is,while in the late stage of creep aging,it is the opposite.Compared with those under 125 MPa and 150 MPa,the alloy creep aged under 175 MPa presents the lowest strength and the best plasticity in the early stage of creep aging,while it is the opposite in the late stage of creep aging. This can be attributed to the synergistic effect between the dislocation strengthening andthe δ ′phase strengthening.