Design And Control Of Recrystal Microstructure Of Ti-6Al-4V Alloy In Hot Die Forging

With the development of aviation industry, the use of aerial materials difficult to deformation, such as titanium alloy and high-temperature alloy, in airplane become wider and wider, therefore, it's urgent to innovate in technologies of preforming and die forging of these materials with existing facilities.To ensure mechanical property and service life, the specified shape, streamline texture and good as-forged microstructure of forgings are expected in forging processes of metal and alloy, since there are some defects of the materials mentioned above in deformation process, such as giant resistance of deformation, small thermal parameter allowance and as-forged microstructure of sensitive to thermal parameter and hard to control, it's difficult to produce qualified forgings with existing facilities and traditional technologies of process design and control.Based on the system study of deformation characters of Ti-6Al-4V alloy and orthogonal experiments, taking the as-forged microstructure and property as objective function, the properties of hot deformation, upsetting process, die forging process and technologies of process design and quality control of Ti-6Al-4V alloy have been analyzed with thermodynamic coupled FEM numerical simulation. The main research findings and new outlooks are as follows:(1) Based on the system study of hot deformation of Ti-6Al-4V alloy and mathematic theory of statistics, a new constitutive equation of parallel model was developed, providing a scientific basis for the numerical simulation of hot forming process of Ti-6Al-4V alloy.(2) Based on the orthogonal experiment results and observation of microstructure of specimens, a recrystal microstructure evolution model of Ti-6Al-4V alloy in hot deformation process was proposed, therefore, its recrystal microstructure could be calculated, predicted and controlled.(3) With FEM numerical simulation and orthogonal experiment results, the isothermal upsetting process of Ti-6Al-4V alloy was studied systematically, and the image mode of thermal parameters, microstructure and property of forgings was developed, thus, a good condition was provided for the process design and microstructure prediction of Ti-6Al-4V alloy in hot die forging.(4) Based on the thoroughly study of several problems that must be solved during numerical simulation, the hot die forging processes of saucer forging and frame forging were designed and simulated, then the billet was optimizing, the deformation defect was analyzed and the recrystal microstructure was predicted, therefore, it provided a sound basis for approved production of the forgings mentioned above.(5) Based on the system analysis and research of Ti-6Al-4V alloy in hot die forging, the integrated technology of design and control of Ti-6Al-4V alloy in hot forming process was generalized, in which the objective function of process design was microstructure uniformity function of forgings and the one of quality control was microstructure stability function, thus, it provided a scientific reference for the optimum design and quality control of aerial materials difficult to deformation in hot die forging.