Research On Differential Temperature Reverse Deep Drawing Of 5A06 Aluminum Alloy Plate

Due to the bending effect and poor plasticity of the aluminum alloy plate,fracture is easy to occur and it is hard to form the deep hollow part by deep drawing process.The differential temperature reverse deep drawing process was proposed to form the deep cups with the ratio of height to diameter exceeding unity.The 5A06 aluminum alloy plate with the thickness of 4.5mm was used,and the differential temperature reverse deep drawing experiment and simulations were conducted to analysis the forming behavior.In order to obtain the mechanical properties under complex stress state,the double-sided sheet hydro-bulging experimental setup was designed and manufactured.The anisotropic flowing stress model under biaxial stress state was deduced and the flowing stress of 5A06 aluminum alloy was tested.The flow stress,(?),is obtained by the hydro-bulging test.The deep drawing experiments and simulations of preformed cups under different die corners were conducted to investigate the bending effect during the deep drawing of aluminum alloy plate.The effect of the die corner radius was numerically studied.A stress and strain gradient along the thickness was induced by the bending effect,which leads to an increase of the longitudinal tensile stress.The maximum gradient occurs at the transient area between the inside flange corner and wall.The longitudinal tensile stress can be reduced by increasing the die corner radius since the bending effect was weakened.The limit drawing depths were obtained through the experiment and the thickness distribution was also investigated.The limit drawing depth increased significantly as the die corner radius increased,and it is 209 mm for 10 relative die corner radius,which increased by 82% than the 4.5 relative die corner radius.When the relative corner radius is 12,fracture can be eliminated and preformed cup with uniform thickness was obtained and maximum thinning is 4%.The stress and strain evolution,the effect of the die corner shapes,temperatures and temperature gradients on the differential temperature reverse deep drawing were numerically analysed.The longitudinal tensile stress and normal strain on both sides of the wall changed reversely when the blank flowed over the die corner,as a result,the stress and strain distribution along thickness became nonuniform.Due to the reverse bending at the transient area between the inside flange corner and wall,a maximum longitudinal stress gradient and tensile stress occurred,which leads to the occurrence of fracture.The increasing of longitudinal tensile stress and stress gradient can be reduced by either using a semicircle sectional die corner or increasing the temperature,since the bending effect was reduced.When the temperature gradient increased,the ultimate tensile strength at the inside flange corner increased and th e fracture was hard to occur,since the temperature at the inside flange corner decreased,while the tensile stress maintains the same.The differential temperature reverse deep drawing setup was designed and manufactured,and the temperature gradient on the preformed cup can be manipulated by controlling the temperature on the preformed cup and the punch.The reverse deep drawing under different die corner shapes,temperatures and temperature gradients were conducted.The optimized die corner shapes,the limited drawing depth under different temperature gradient were obtained,the fracture mechanism of deep aluminum alloy plate during the reverse deep drawing was investigated,The effect of the temperature gradient on the thickness distribution was analyzed.The limit drawing depth increases when changing the die corner shapes.For a semicircle sectional die corner,the limit drawing depth was 116 mm,which increased by 47% comparing that for a flat die corner shape.However,the fracture can not be eliminated by using the semicircle die corner.The limit drawing depth increased significantly by using a differential temperature reverse deep drawing method.As a differential temperature filed was performed on the preformed cup,the temperature at the inside flange corner becomes lower than that at the flange area,which makes the strength area becomes larger than the other areas and the fracture is hard to occur.The limit drawing depth is further increased as the temperature gradient increased.For the temperature gradient of 25?,the limit drawing depth is 76 mm and it increased to 276 mm as the temperature increased to 50?.The fracture can be eliminated as the temperature gradient increased over100,and the 430 mm deep cups with 1.43 ratio of the height to diameter was formed.The thickness variation was also reduced as the temperature gradients increases since the thinning at the bottom and the thickening at the wall was reduced.The EBSD analysis and micro hardness testing were performed to investigate the effect of temperature and temperature gradient on the grain size and the hardness distribution.When the temperature is lower than 400?,the microstructure was stable and the grain size varies a little.The hardness and its difference between different areas of the blank decreases as the temperature increased since the dynamic recovery was increased.