Study On High Speed DC Casting Process Of Hypereutectic Al-Si Alloys

The size of primary silicon was refined and its distribution was improved by high speed DC casting in this paper.Fistly,the temperature filed and flow field in A390 alloy ingot were studied by the by Fluent simulative software.The temperature and the melt flow in different conditions of casting were investigated by changing distribution methods,materials of molds and cating conditions.The microstructure evolution of A390,Al-20%Si,Al-23%Si alloys ingots cast in high DC casting was worked out.The main results are followings:(1)The effects of casting conditions on temperature field and flow fied in different casting temperatures,casting speeds and second cooling intensities were determined by numural simulation.Increasing in casting temperature increases flow velocity in surface of ingots.When casting speed increses the cooling rate increses in the part from 1/2 radius to surface and depth of liquid cave.Increasing in second cooling intensity increase cooling rate in the ingot surface.(2)When the casting speed increases from 160mm/min to 250mm/min,the A390 alloy microstructure is mainly composed of primary Si,Al + Si eutectic and CuAl2,the distribution of primary silicon is relatively uniform,the higher the casting speed the smaller the size of primary silicon.When the casting speed is 160mm/min the size of primary selicon is 21.36?m,19.84?m,and 23.99?m in 0R,1/2R and 1R of the ingots respectively.When the casting speed is 200mm/min the size of primary selicon is 20.73pm,17.36?m,and 22.99?m in 0R,1/2R and 1R of the ingots respectively.When the casting speed is 250mm/min the size of primary selicon is 20.73?m,16.25?m,and 22.51 ?m in 0R,1/2R and 1R of the ingots respectively.(3)After dealing with the P modification Al-20%Si and Al-23%Si alloy the distribution of primary silicon is relatively uniform in 200mm/min casting speed,size of primary silicon of Al-20%Si is significantly less than that of Al-23%Si,so that we can be seen that the change of silicon content has obvious influence on the size of primary silicon.When the casting speed is 200mm/min the size of primary selicon is 30.55?m,23.34?m,and 25.34?m in 0R,1/2R and 1R of the Al-20%Si ingots respectively and the size of primary selicon is 33.11?m,29.6?m,and 33.44?m in 0R,1/2R and 1R of the Al-23%Si ingots respectively.(4)There are different morphology of primary silicon in Al-20%Si ingots including both the octahedral crystal silicon with holes and no hole and plate-like morphology of primary silicon.Primary silicon particles with big size and complex morphology appeared in Al-23%Si ingots.