Research On Rheological Forming And Subsequent Annealing Process Of Compound Energy-field Roll-Casting AZ31B Mg Alloy

With low-density, high specific strength and specific stiffness, excellent electromagnetic shielding, etc., Mg alloy has been widely used in the field of transport, electrical and electronic industry, metallurgy, aerospace, defense and military antiradiation and so on. Therefore it’s known as "green structural material of the21st century". The roll-casting process of Mg alloy strip has the characteristics of rapid solidification, energy-saving, low-cost. Electromagnetic and ultrasonic are applied in the process of roll-casting forming, and which refine the grain and improve the plasticity. The paper uses the large-scale simulation software ANSYS to establish the finite element model and treat the essential boundary in condition, finally simulate and analysis the temperature field and flow field on the process of electromagnetic and ultrasonic roll-casting AZ31B Mg alloy. Secondly, study and analysis the influence of annealing on the Mg alloy strip absequent processability. Main contents and results as followed:(1) Analysising simply the basic theory of electromagnetic field, ultrasonic field, electromagnetic and ultrasonic compound energy-field, and investigating mechanism of the external field on the process of roll-casting Mg alloy.(2) Establishing a3d finite element model of roll-casting Mg alloy, simulating and analysising the flow field of nozzle which setting or not the shunt block. The result shows that the Mg alloy melt flow field after the nozzle by setting shunt block.(3) Establishing the electromagnetic field3d finite element model, and imposing the boundary conditions of electromagnetic, simulating to calculate the magnetic induction and Lorentz force value and distribution in the process of Mg alloy roll-casting, and then imposing the boundary conditions of ultrasonic vibration, obtaining temperature field and flow field distribution of Mg alloy electromagnetic ultrasonic roll-casting under different roll-casting process parameters. It is showed by contrast:The Lorentz force of electromagnetic induction makes Mg melt a horizontal velocity component in the flow process, strengthen the intensity of its heat transfer with the surrounding,the melt outlet speed become more uniform with the ultrasonic vibration shunt and acoustic streaming stirring,thus narrow the melt cooling area,prolong the casting and rolling area,improve the strip performance and the outlet temperature is relatively lower. Hence the head box temperature of Mg alloy electromagnetic ultrasonic roll-casting should be reasonably controlled at695℃-705℃, the roll-casting velocity should be at2.2m/min-2.6m/min.(4) The effect of annealing temperature and time on the microstructure and mechanical properties of AZ31B Mg alloy roll-casting sheets were investigated, the specimens are deformed by general roll-casting and electromagnetic and ultrasonic roll-casting. By metallographic microstructure, mechanical properties, spectroscopy analysis and hardness testing, etc., a series of experiments show:the begin recrystallization temperature of general and electromagnetic and ultrasonic roll-casting Mg strip are respectively300℃and250℃.At the annealing of250℃and4h, no obvious re-crystallization occurred for the general Mg strip sheet.In the condition of annealing at300℃and4h, the average grain diameter were14-19μm,8-13μm for the general Mg strip sheet and electromagnetic and ultrasonic Mg strip sheet, respectively; the precipitates of general Mg roll-casting sheet with thicker size were enriched on the grain boundaries; the values of HBS, σb, σ0.2and δ of electromagnetic and ultrasonic Mg strip are improved by4.7%,17.2%,34.1%,74.6%, compare to general Mg sheet. The specimens are annealed at400℃, the grains become coarse within1h.