Study On The Heat Treatment Process And Anisotropy Of 2A66 Aluminum-lithium Alloy

Al-Cu-Li alloy of 2A66 is developed by the domestic institute independently, it has a broad application prospect in the field of aerospace, owing to its relatively light weight, high speicific strength, good plasticity and processing performance. Studying the heat treatment process on microstructure and properties of 2A66 alloy can acheive a optimize combination of strength, ductility and corrosion resistance, which can further promote its application in the aerospace industry. In this paper, the hardening behavior, mechanical properties, the evolution rules of the precipitates, the in-plane anisotropy and texture component of the 2A66 thin sheet alloy at different heat treatment conditions were investigated by hardness tests, tensile tests, optical microscope（OM）, differential scanning calorimetry（DSC）, scanning electron microscope（SEM）, transmission electron microscopy（TEM） and Electron Back-Scatter Diffraction（EBSD）. Not only to optimize the heat treatment process and analyse the evolution of the precipitates during aging process, but also measure its in-plane anisotropy and texture component at different heat treatment conditions. The main conclusions are shown as follows:（1） The overburnt temperature of 2A66 Al-Li alloy is 525℃, the suitable solution temperature and time of this alloy are 520℃ and 90 minutes respectively. In the process of single-stage aging, the higher the aging temperature, the shorter the time for peak value. The alloy could get a good combination of strength and plasticity after aged at165℃ for 64 h, the tensile strength, yield strength and elongation of the alloy were526.5MPa, 448.9 MPa and 10.1%.（2） The favorable double-stage aging of 2A66 alloy was 200℃/12h+165℃/12 h, at this condition, the tensile strength, yield strength and elongation of the alloy were527.1MPa, 490.7 MPa and 7.5%. The favorable RRA treatment of 2A66 alloy was165℃/24h+220℃/40min+165℃/24 h. At this condition, the tensile strength, yield strength and elongation of the alloy were 519.8MPa, 469.7 MPa and 9.8%.（3） The precipitation sequence in the 2A66 Al-Li alloy during 165℃ single-stage aging is: α supersaturated solid solution（sss）→G.P. zone+δ’→θ’+δ’→θ’+δ’+T₁→θ’+T₁.At the early stage of aging, the main source of strengthening for the alloy is the G.P.zone, δ’ phase and θ’ phase. At the peak of aging, the θ’ phase and T₁ phase are the main strengthening phases.（4） The anisotropy of the original state, solid solution and aging state of 2A66Al-Li alloy decreases. The main texture in the original samples is the cube texture, the C component, B component and S component also exist. But, the main texture in the solid solution samples changed into the rotated cube texture. The main texture in the samples after aging treatment is still the rotated cube texture, and the R component appearances.（5） During 165℃ single-stage aging, before the peak aging, the anisotropy of the alloy reduced with the increase of aging time; when the alloy was over-aged, the anisotropy of the alloy increased. The anisotropy of ductility is more serious than that of strength.