Research On The Hot Deformation Behavior And High-speed Gas Bulging Of 2A12 Aluminum Alloy Sheet

With the development of automobile industry and aerospace industry,the application of complex thin-walled metal components is more and more widely.Due to the demand for lightweight,such components mostly use lightweight and high performance materials such as aluminum alloy,magnesium alloy and titanium alloy.Such materials have low plasticity and poor forming performance at room temperature,and usually need to form complex thin-walled components in hot state.High-speed hot gas bulging has been successfully applied in mass production of complex thin-walled metal components due to its high production efficiency.However,in the traditional high-speed hot gas bulging,the rapid filling of ambient temperature gas will reduce the temperature in the local area of the high-temperature slab and form a non-uniform temperature field.At the same time,the air pressure in the closed space formed by the slab and the die cavity is also uneven during the filling process.Unreasonable and uncontrollable temperature distribution and pressure distribution seriously affect the forming quality of complex thin-walled metal components.In order to solve the above problems,this paper proposes a near-isotherm isobaric high-speed hot gas bulging method.The isothermal isobaric environment is established by filling high-pressure gas on both sides of the slab at the same time,and the high-speed bulging is realized by rapid degassing on one side.In this paper,2A12 aluminum alloy sheet was taken as the research object,and the deformation behavior of the material at different temperatures and different strain rates was studied through high-temperature uniaxial tensile test.The rapid bulging process of cup and ball bottom parts at high temperature was analyzed by finite element simulation,and the contour shape,stress-strain and wall thickness distribution of bulging parts at different temperatures and strain rates were studied.Through the high-speed hot gas bulging experiment of sheet metal,the contour shape,strain and wall thickness distribution of bulging parts obtained by rapid inflation and rapid discharge were studied.The mechanical properties and fracture morphology of 2A12 aluminum alloy sheet under different temperature and strain rate were studied by high temperature uniaxial tensile test.When the temperature is 450℃and the strain rate is 0.1s^-1,the ultimate elongation of the material is the largest,up to 174.3%,and the uniform deformation area accounts for the largest proportion of 39.56%.The uniform deformation ability is the strongest.With the increase of temperature,the strain rate sensitivity index m increases,and the m value is 0.162 at 475℃,indicating that the strain rate hardening ability of the material increases with the increase of temperature.In the range of 350℃to 450℃,the fracture mode of the material is transgranular ductile fracture.In the range of 450℃to 500℃,the fracture mode is a mixture of transgranular ductile fracture and intergranular brittle fracture.Under the same temperature conditions,the dimple distribution at the fracture surface of the uniaxial tensile specimen with strain rate of0.1s^-1is the most uniform.The profile shape,stress-strain and wall thickness distribution of bulging parts under different temperatures and strain rates were studied through the simulation analysis of hot gas bulging of sheet.When the bulging height is consistent,at 450°C,the fillet radius of the bulging part is the smallest,the fitting degree between the contour shape and the mold cavity is the highest,the stress and strain values of the bulging part are the smallest,and the wall thickness distribution is the most uniform.When the strain rate is 1s^-1,the stress value of the bulging part is the largest,the strain value is the smallest,the strain rate hardening phenomenon is the most obvious,and the wall thickness distribution is the most uniform.When the temperature is 450°C and the strain rate magnitude is 1s^-1,the wall thickness range of the bulging part is 0.557 mm.Compared with other conditions,the wall thickness range is the smallest and the distribution is the most uniform.Through the high speed hot gas bulging experiment of sheet,the forming accuracy,strain distribution and wall thickness distribution of bulging parts obtained by rapid inflation and rapid discharge were studied.When forming cup-shaped parts,the die-fitting degree of the bulging part obtained by rapid inflation process is 87.5%,the fillet radius is 2.75 mm,the die-fitting degree of the bulging part obtained by rapid discharge process is 89.5%,and the minimum fillet radius is 2.5 mm,indicating that the rapid discharge process has higher forming accuracy.When forming the ball bottom,the 20 mm deep ball bottom was successfully formed by rapid inflation and rapid discharge.At 450°C,the wall thickness range of the bulging part obtained by the surrounding rapid inflation process was 0.1 mm,and the wall thickness range of the bulging part obtained by the rapid discharge process was 0.07 mm.It is known that the wall thickness distribution of the bulging part obtained by the rapid discharge process is more uniform.When forming a 30 mm deep spherical base,the wall thickness of the bulging parts obtained by the rapid air-filling process is seriously reduced,and cracks occur.In the temperature range of400°C-450°C,the rapid air-filling process is used to establish a near-isothermal isobaric environment,and the 30 mm deep spherical base is successfully bulging.The problem of part cracking in the traditional forming is solved,and the superiority of the rapid air-filling process in forming deep cavity thin-walled parts is proved.