Preparation Of Semi-solid A356-RE Alloy Slurry Under Two-way Electromagnetic Stirring

The effective control of solidification microstructure morphology and size is the key to the preparation of alloy slurry,it is also the constant pursuit of the semi-solid processing field.At the same time,it is the core content of materials science research and engineering applications.Therefore,effectively controlling the material solidification process and obtaining high-quality metal slurry which is of great significance for semi-solid processing.Semi-solid processing as an emerging material processing technology has a significant characteristics near-net shape,high-efficiency,energy-saving and clean and environmental protection,which is known as the green material processing technology in the 21 st century.This work based on preparation high performance semi-solid aluminum alloy slurry,which be made by material electromagnetic processing technology(formed by the combination semi-solid processing technology and magnetic fluid mechanics)and rare earth elements on the solidification process of aluminum alloy.The evolution law and performance of solidification microstructure of aluminum alloy under the combined action of electromagnetic field and rare earths elements were studied.The main research contents and results are briefly summarized as follows.(1)Combined two-way electromagnetic stirring with rare earths on the solidification process of A356 aluminum alloy to research the effect of magnetic field frequency(10,20,30,40Hz),electromagnetic stirring ways and rare earth(0%RE,0.5%Ce,0.3%La+0.2%Yb)on the grain size,morphology and fractal dimension of primary phase ?-Al.The results show that30 Hz is a suitable frequency for obtaining the primary phase with small size and round morphology,and the primary phase is smallest in size and roundest in shape under 30 Hz two-way continuous stirring with mixed rare earths,the average circle diameter is 36.4?m,the shape factor is 0.82 and the fractal dimension is 1.3133.(2)Study and analysis the influence of magnetic field frequency(5,15,25,35 Hz)on the solidification structure and the distribution rule of rare earth element La in radial direction at different radial positions(0R,0.7R,1R)of alloy ingot under two-way continuous electromagnetic stirring.The results show that with increasing frequency,the size of the primary phase gradually refines and spheroidizes,and the morphology of rare earth elements evolves from acicular to punctiform.The size of the primary phase at 25 Hz and 0.7R is thesmallest,the average circle diameter is 36.2?m,the shape factor is 0.83,and La is a rare-earth element distributed in fine dots.(3)Preparation of semi-solid A356-Ce alloy slurry by two-way intermittent electromagnetic stirring technology.The effects of magnetic field frequency(10,20,30,40Hz)and intermittent time(0,1,3,5s)on the microstructure and mechanical properties were studied.The results show that the degree of spheroidization of primary grains is the best at 30 Hz and intermittent time3 s.The average equal-area diameter is 35.2?m and the shape factor is 0.81.In addition,the effect of 30 Hz single-way continuous stirring,30 Hz two-way intermittent 3s stirring,conventional casting on the tensile properties and fracture morphology of alloy were researched by SEM.The results show that the tensile strength and plasticity of alloy are improved by 30 Hz intermittent 3s stirring.The fracture mode transitions from brittle fracture to a mixed mode of brittle fracture and ductile fracture.(4)Combined with two-way electromagnetic stirring and isothermal insulation technology,proposed a new composite slurry preparation processing.Two-way continuous continuous electromagnetic stirring and isothermal heat treatment.The effect of isothermal temperature 580~610? and isothermal time 3~15min on the solidification structure after30 Hz two-way continuous electromagnetic stirring was analyzed.The results show that the primary phase is gradually refined and spheroidized with increasing temperature and time.The size and the degree of spheroidization of primary phaseare are best under the heat treatment conditions of 600°C and 7min.the average circular diameter is 29.4?m,the shape factor is 0.86.The innovation of this paper is to explore the rules of solidification microstructure evolution of aluminum alloy under the action of two-way electromagnetic stirring and rare earth elements,analyzing the flow law of molten metal and the existence and distribution of rare earth elements in alloys under different stirring modes.In addition,based on the fractal theory,fractal dimension was used to quantify the grain size refinement and roundness morphology of the primary ?-Al,so an indirect bridge could be established to analyze the relationship between microstructure and properties of metal materials.