Study On The Heat Treatment Process, Microstructure And Properties Of 2297 Alloy

Al-Cu-Li alloy of 2297 has a broad application prospect in the field of aerospace, owing to its relatively light weight, high specific strength, good weldability and fatigue resistance. The solution and aging process were studied to achieve a optimum combination of strength and ductility during heat treatment process. In this paper, the mechanical properties and microstructure of the 2297 alloy were investigated by tensile tests, optical microscope(OM), scanning electron microscope(SEM) and transmission electron microscopy(TEM). The main conclusions are shown as follows:① The 2297 alloy were first soluted at the temperature from 500℃ to 540℃, than aged by 160℃/24 h. The result shows: with the raising solution temperature form 500℃ to 520 ℃, the residual gradually dissolved into the matrix and the hardness increased. The alloy reached to the peak of hardness at the temperature of 520℃. When the temperature increased to 540 ℃,the number of secondary phases didn’t change obviously,and the size of grain became larger.When the solution temperature was 520℃ and the holding time was between 20 minutes and 60 minutes,the number of secondary phases decreased gradually and the hardness increased with the prolonged holding time. When the holding time was more than 60 minutes,the number of secondary phases changed little, the size became larger and the hardness decreased.So the suitable solution temperature and time of the alloy is 520℃ and 60 minutes respectively.② Adopted the solution process of 520℃/60 min. A series of experiment on aging treatment was done.The result shows :with raising the aging temperature,the less time the alloy need to reach to the peak aging. The tensile strength of the alloy increased before the alloy reached the peak aging. With the extension the of aging time, the tensile strength decreased.While the plasticity decreased with the growth of aging time. The proper aging process is 180℃/48 h, the ultimate tensile strength is 471 MPa, the yield strength is 378 MPa and the elongation is 15.3%.③ Adding pre-deformation which is from 0 to 8% before aging treatment,the time of the alloy with 2% pre-deformation need to reach to the peak aging was 60 h,the ultimate tensile strength is 471 MPa, the yield strength is 378 MPa and the elongation is 15.3%.When the pre-deformation increased to 5%,the time for the alloy took to reach to the peak aging has been shorten obviously to 24 h. The ultimate tensile strength increased 10 MPa,the the yield strength increased 45 MPa while its elongation decreased 0.5%.With the pre-deformation increased to 8%, the time for the alloy took to reach to the peak aging decreased to 12 h,but the mechanical properties of the alloy decreased little. The suitable aging process is 5% pre-deformation+180℃/24 h. The ultimate tensile strength is 480 MPa, the yield strength is 423 MPa and the elongation is 16%.