Simulation Of The Temperature Field And Flow Field Of Al-Si Alloy Melt During The Cooling Process And Prediction Of Microstructure In Solid-state

Al-Si alloys have light weight and excellent casting properties, and are widely used for many industries such as aerospace, electric power, machinery, transportation.In order to improve the performace, it is necessary to improve the morphology of primary silicon in Al-Si alloy and to grain refinement, its essence is to control the microstructure changes during the cooling process. The temperature field and flow field in the cooling process affect the solute distribution and structure changes of liquid phase directly, so they have a significant impact on solidification microstructure.But it’s difficult to measure the temperature field and flow field during the cooling process by experiment, this paper study the diversification of the temperature field and flow field of Al-Si alloy melt during the cooling proces by computers, and test by experiments.This paper simulates the diversification of the temperature field and flow field of Al-Si alloy melt during the cooling proces under different conditions, we obtained how taper (of δ:4°to6°), length (L:500mm～200mm), angle(θ) between its axis and the vertical (θ:0°～30°) of the conical tube which outlet diameter is25mm and thickness is5mm, and melt temperature(To:800℃～950℃) at the entrance influence the temperature field and flow field of alloy melt.Furthmoer, the impacts of temperature field and flow field to solidification structure were analyzed, then the technical condtions suited to rapid cooling forming of Al-Si alloy were obtained. Simulation results show as follows:(1)The ability to temperature regulation of alloy melt temperature field in conical tube is much better than that of in straight tube. The temperature drop of alloy melt in traight tube are74.785℃and78.107℃, when θ is0°, To is750℃and800℃; However, the temperature drop of alloy melt in conical tube are226.9℃and239.8℃, when θ is0°, To is900℃and950℃.The outlet temperatures of alloy melt in traight tube are100.148℃and114.8℃, when θ is30°, To is750℃and800℃; However, the temperature drop of alloy melt in conical tube are189.8℃and226.6℃, when θ is30°, To is900℃and950℃. The melt distribution of temperature field is more uniform in conical tube than that of in straight tube at the same section and the temperature gradient gradually decreases from the entrance to the outlet, that is beneficial to the crystallization of the alloy.(2) When the length of graphite tubes changes from200mm to500mm, the taper of graphite tubes changes from2°to6°, the angle between the axis of graphite tubes and the vertical changes from0°to30°and the vertical and the melt temperature at the entrance changes from800℃to950℃, the distribution of the alloy melt temperature is affected by these four elements above and the tilt angle of graphite tube. For the same conical tube, The higher melt temperature at the entrance, the greater temperature drop of alloy melt; The great taper of graphite tube, the greater temperature drop of alloy melt. When0is0°, the melt temperature field distribution is relatively uniform from from the edge to the core part and a temperature gradient, the edge temperature is lower and temperature drop is faster while the core is high and temperature drop is slow; When0is30°, the melt temperature field distribution is uneven owing to gravity.(3)The distribution of flow fluid of allouy melt in conical tube is similar to that of temperature field. But there is a turning point on speed close to the entrance of the tube wall, that lead to a transition after the melt enter the tube and ensure the uniformity of the melt flow field.Furthermore, the alloy melt solidification is affected by the turning point on speed.(4)A formula for the colling effect of graphit tube is proposed and by this formula, a optimal technological parameters is predicted are as follows:the length of graphite tube is300mm, the taper of graphite is6°, the angle between the axis of graphite tubes and the vertical is0°, and the melt temperature at the entrance is900℃. Casting under this condition, microstructure of fine and uniform can be available.(5) Doing experiments to verification optimization results. When the billet was cast at900℃, the grain were uniform, fine and globular, and the average sizes of primary a-Al phase andf primary silicon were23μm～35μm and10.3μm. This is consistent with Forecast results.