The Reduction Of Quenching Residual Stress For7A85Aluminum Alloy Joint Die Forging By Mold Compression

Abstract:The7A85joint that supports wing is an extremely important load-bearing part, which needs to be quenched to improve strength, toughness, corrosion resistance, anti-fatigue and other comprehensive mechanical properties, but the quenching residual stress can cause deformation and even crack, which has become one of the major difficulties for production and research. The formation and evolution of residual stress of the7A85main supporting joint forging for large aircraft was analyzed in this paper, and the local mold press method to reduce quenching residual stress was proposed. The simulation and experiments of the whole process for test sample were carried out. The main research contents include:(1) The thermal properties measurement experiments of7A85aluminum alloy were carry out to get the specific heat, thermal conductivity and thermal expansion coefficient from20℃to500℃, which provides basic material data for7A85aluminum alloy forging residual stress analysis.(2) Based on heat transfer and thermal elastic-plastic mechanic theory, the mathematical model and finite element simulation model of quenching process for7A85aluminum alloy forging were established, which got the result of quenching stress field and temperature field by using ABAQUS finite element simulation software. Results show that: the inner stress is tensile while the external is compressive after quenching, residual stress concentration locations are rounded and intersection between web plate and stiffened rib. The stress concentration level is mainly distributed from200MPa to400MPa; the maximum deformation is1mm after quenching.(3) Based on the elastic-plastic stress theory, the mathematical model of cold deformation of7A85aluminum alloy was established. According to the quenching residual stress distribution, the local press mold and compression simulation were finished. Researches show that:Pressing 3%for cold compression deformation is appropriate, which can decrease50%-80%of residual stress.(4) Rectangular specimens of100x60x40mm were fabricated with7A85aluminum alloy, and the quenching and cold deformation experiments were processed to get residual stress respectively with the same process of die forging simulation; The quenching and cold deformation simulation were carried out to get their residual stress; The absolute error is less than40MPa by comparing the experimental and simulation stress, which indicates that the simulation of quenching and cold deformation for7A85aluminum alloy has good accuracy. There are55charts,9tables,69references.