Effects of Pre-Stretching on Creep Behavior, Mechanical Property and Microstructure in Creep Aging of Al-Cu-Li Alloy

Jin Zhang,Mingan Chen,Zhen Jiang,Fushun Xu

doi:10.3390/ma12030333

Abstract

The effects of pre-stretching on creep behavior, mechanical properties and microstructure during the creep aging process of Al-Cu-Li alloy were investigated. AA2195 was taken as the representative of Al-Cu-Li alloys. It is found that the total creep strain and strength property of creep aged AA2195 specimens can be improved through effective pre-stretching. Unlike with artificial aging, yield strength increased increasing by 47%. The TEM images show that the constitution of aging precipitates in the creep-aged specimens are obviously changed by pre-stretching. Precipitates in the 2% pre-stretched specimen are mainly composed of T1 phase, while a great amount of θ’ phase accompanied with a few T1 phase were found in the non-pre-stretched specimen. Moreover, pre-stretching introduces many dislocations which benefit the creep deformation, but the increasing dislocation density also accelerates the nucleation and growth of the precipitates as well. The premature T1 phase has a great blocking effect to the dislocation motion, creating a lower decrease rate but a longer duration in the early creep stage. Except for the initial dislocations, the dislocation motion in the creep aging process is also a favorable factor to precipitate the T1 phase.

Highlights

As one of the currently popular aeronautic and astronautic structural materials, Al-Cu-Li alloys have received worldwide attention and been developed rapidly in relevant production and application for their valuable combination of properties, such as low weight, high modulus and high specific strength [1,2,3]
As an excellent representative of Al-Cu-Li alloys, AA2195 has replaced the incumbent structural material (AA2219) for the cryogenic fuel tank on the space shuttle, as it provides an effective way of lowering the structural weight
The T1 phase formed in aluminum {111} planes is considered as the primary strengthening phase in Al-Cu-Li alloys [4,5,6]

Summary

Introduction

As one of the currently popular aeronautic and astronautic structural materials, Al-Cu-Li alloys have received worldwide attention and been developed rapidly in relevant production and application for their valuable combination of properties, such as low weight, high modulus and high specific strength [1,2,3]. As an excellent representative of Al-Cu-Li alloys, AA2195 has replaced the incumbent structural material (AA2219) for the cryogenic fuel tank on the space shuttle, as it provides an effective way of lowering the structural weight. The T1 phase formed in aluminum {111} planes is considered as the primary strengthening phase in Al-Cu-Li alloys [4,5,6]. Plastic deformation prior to aging enhances the aging kinetics and increases the number density of fine strengthening precipitates through the introduction of dislocations acting as preferential heterogeneous matrix nucleation sites for the T1 phase [7]. Cassada et al [8] found that the volume fraction of fine matrix T1 phase is enhanced by the effect of pre-deformation. Gable et al [10] conducted quantitative research and found that the size and quantity of Materials 2019, 12, 333; doi:10.3390/ma12030333 www.mdpi.com/journal/materials

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Conclusion