Study On The Heat Treatment Technology Of 2297 Al-Li Alloys And Its Mechanical Behavior Of Different Temperatures

2297 aluminum-lithium alloy has broad application prospects in the aerospace field because of its high strength, high fracture toughness, high resistance to stress corrosion and many other advantages. For instance, aluminum-lithium alloys has applied on the "lunar rover" for a pretty long time. In addition, the application environment of 2297 aluminum-lithium alloy is the moon, on which the DIF is so large, so the research on its service performance at high and low temperature is necessary. For this reason, this article will mainly focus on two aspects: 1) Get a systematic research on the effect of thermomechanical processing(TMTP) on microstructure and properties of the alloy, find some guidelines to optimize the process system of 2297 aluminum-lithium alloy, wherein the TMTP comprises solution treatment, aging temperature and different pre-deformation before aging; 2) Get a preliminary study on the mechanical property and the corresponding deformation mechanism of 2297 Al-Li alloy at high temperature and low temperature respectively.The TMTP of hot rolled 2297 aluminum-lithium alloy are carried out under different solution temperature 、 solution time 、 aging temperature and different pre-deformation before aging.The results showed that:(1) When the pre-deformation is not introduced before the aging, an optimum comprehensive mechanical properties is obtained with 530 ℃ / 60 min solution + 175 ℃ / 24 h aging treatment.(2) When the pre-deformation is introduced before the aging, an optimum comprehensive mechanical properties is obtained with 530 ℃ / 60 min solution + 10% pre-deformation + 175 ℃ / 24 h aging treatment.(3) Compare to the process system with no pre-deformation,the yield strength under 10% pre-deformation increased by 18%, the tensile strength increased by 10%, and the elongation decreases slightly. After the introduction of pre-deformation, an appropriate amount of dislocation come into being, promote the nucleation of T1 phase, precipitation of θ phase decreases obviously. Phase T1 is the main strengthening phase of aluminum-lithium alloy, High density, so that a substantial increase in the strength of the alloy, alloy toughness has been effectively improved. High density T1 phase can pinning the dislocation effectively, so that the strength of the alloy get a substantial increasement. The strength and toughness of the alloy has been improved effectively. The tension test on Aged 2297 Al-Li alloy at high temperature(150℃、300℃、450℃) and low temperature(-180℃) are carried out, mechanical property and deformation mechanism under different temperature are investigated.The results showed that:(1) When the tension test is carried out under a high temperature and same strain rate, flow stress with deformation temperature decreases, the flow stress decreases with the increasing of deformation temperature. But at a strain rate of 0.0001 / s, and deformation temperature of 300 ℃, the elongation does not conform to this conventional law. Maybe the second phase get a excessive growth at 300 ℃, thus the plasticity is affected. At the same deformation temperature, the flow stress increases with the increasing of strain rate, the elongation decreases with the increasing of strain rate.(2) When the tension test is carried out under a low temperature, comparing to the test under room temperature, the strength of the alloy increases significantly, and the plasticity increases slightly. Due to the decrease of deformation temperature, short range resistance of the dislocation in the crystal increases sharply, plane slip is restrained, the strain hardening deformation uniformityrate increases, therefore, the strength and plasticity of the alloy increased.