Study On Hot Deformation Behavior Of Al-Si Coating 22MnB5 High Strength Steel And Hot Forming Of Automobile B-Pillar

Variable-thickness Rolled Blanks(VRB)is a kind of sheet with uniform thickness changes along the rolling direction.VRB has a reasonable thickness distribution according to the strength requirements.Compared with the same thickness plate,the lightweight effect is significant while meeting the strength requirements of the parts.In addition,the use of high strength steel in the automobile body can greatly reduce the weight of the body,improve the automobile body strength.Therefore,the combination of VRB and high strength steel is applied to the manufacturing of automobile body structure parts,which is in line with the development trend of lightweight of modern automobile body.However,there are more variables in the hot forming process of VRB high strength steel,the forming conditions are complex,and the difficulty of quality control of parts is greatly increased.The Al-Si coating 22Mn B5 high strength steel thickened plate as the experimental material,the automobile B-pillar as the research object is taken.The research method combining experiment and numerical simulation is adopted.The main research work was completed as follows:Based on the actual conditions of hot forming of 22Mn B5 high strength steel,Gleeble thermal simulation test scheme was developed and the true stress-strain curve was obtained for strain rate of 0.1s^-1-10s^-1 and deformation temperature of 750?-900?.The effects of different strain rates and deformation temperatures on rheological behavior were analyzed.Based on the true stress-strain data,Arrhenius constitutive model for high strength steel of the Al-Si coating 22Mn B5 is established,the constitutive model parameters of different strain point is solved for strain range of 0.1?0.45 by using linear regression method,7 order polynomial is derived between the strain and the constitutive model parameters.The Arrhenius constitutive model for the Al-Si coating 22Mn B5 is established considering the effects of strain.The predicted value of the constitutive model is compared with the experimental value of the thermal simulation test.The result shows that the constitutive model has good prediction accuracy in the whole strain range,and the high temperature constitutive relationship of Al-Si coated 22Mn B5 high-strength steel is effective.A hot forming die for automobile B pillar with a blank holder and a pressure core was designed for VRB.The heat transfer coefficients between plate and mold,mold and cooling water is solved.Based on ABAQUS software,the finite element model for the hot forming of VRB automobile B-pillar is developed with the established constitutive model,the designed mold and the calculated heat transfer coefficient.Depending on numerical simulation research,temperature and stress state changes caused by the material transfer for the hot forming of VRB 22Mn B5 high strength steel were analyzed,the influence of the law was put forward for different friction coefficient and forming speed on the hot forming of automotive B-pillar.The result shows that good forming effect can be obtained when the friction coefficient is less than 0.35 and the forming speed is 100mm/s.Finally,the reliability of the process parameters was verified by experiments.