Numerical And Experimental Study On Solid State Additive Manufacture Of AZ31 Magnesium Alloy

Magnesium alloy has high strength and ductility,and as the lightest alloy material,it has broad application prospects in medical,automotive and aerospace fields.The traditional manufacturing industry has great limitations for the production of complex structural parts.3D printing provides a new idea for the additive manufacturing of magnesium alloys.Among them,Friction stir additive manufacture(FSAM)technology is a new type of solid additive technology.Compared with molten additive technology,there is no metal melting and solidification in the application of aluminum,magnesium and other light alloys.There are fewer metallurgical defects,which can be applied to the addition of large components and has a high molding quality.This thesis takes AZ31 magnesium alloy FSAM as the research object,and uses a combination of computational fluid dynamics simulation,empirical formula derivation and experiment to study the influence of process parameters on the rheology,temperature field and strain rate of materials.This paper deduces the rapid prediction algorithm for the grain size and microhardness of the recrystallized structure in the FSAM additive zone,which provides a theoretical basis for the optimization of the FSAM process parameters and the improvement of the mechanical properties of the additive sample.The main research contents of the paper are as follows:(1)Numerical analysis of temperature-material rheological coupling in FSAM process.A computational fluid dynamics model for multi-layer sheet additive molding was established to study the influence of the rotation speed and traveling speed of the stirring tool on the temperature field,strain rate and material rheology,and was verified by comparison with experimental measurements.The research results show that the speed of the stirring tool is the main factor affecting the additive forming.During the FSAM process of the three-layer AZ31 magnesium alloy plate,when the speed of the stirring tool is 60 mm / min and the rotation speed is within the range of 1000 ? 1600 rpm,as the speed of the stirring tool increases,the temperatures of the plate increase and the deformation rates increase,the flow velocities between the layers are increased,and the materials are fully mixed.The travel speed has little effect on the temperature and flow fields in the FSAM process.(2)Prediction of grain size and microhardness in the additive zone.Calculate the Zener-Hollomon parameter of the thermal deformation process of the magnesium alloy material in the additive zone,and use the empirical formula method to correlate the Z parameter with the recrystallization grain size in the additive zone.Combining the HallPetch formula,a method for predicting the microscopic properties of AZ31 magnesium alloy is proposed,and the influence of process parameters on the microstructure and properties is discussed.In the three-layer AZ31 magnesium alloy plate FSAM process,when the speed of the stirring tool is 60 mm / min and the rotation speed is within 1000 ? 1600 rpm,the recrystallized grain size increases with the increase of the rotation speed of the stirring head.Within the range of the process parameters,the microhardness of the additive zone showed a downward trend with the increase of rotation speed.Among them,the average hardness of the additive zone of the FSAM sample at 1000 rpm was the largest.(3)Research on FSAM processing and macro mechanical properties.The experimental method was used to study the FSAM processing and molding.The results show that the cause of the defects in the FSAM process is not only related to the process parameters such as the speed of the stirring tool,the traveling speed,the inclination angle,and the amount of pressure on the shoulder,but also the number of layers of the additive plate,Additive starting point and end point,etc.,choose the appropriate parameters to avoid the occurrence of macro defects.When the speed of the stirring tool is 60 mm / min and the rotation speed is within the range of 1000 ? 1600 rpm,the tensile strength of the three-layer AZ31 magnesium alloy FSAM sample shows a downward trend with the increase of the rotation speed of the stirring head.By adding graphene nanoplatelets(GNNs)to the AZ31 magnesium alloy plate FSAM process,the elastic modulus and nano-hardness of the sample can be improved.