Influence of plate length and plate cooling rate on solidification and microstructure of A356 alloy produced by oblique plate
(Department of Mechanical Engineering, Indian Institute of Science, Bangalore 560012, India)
Abstract: A356 alloy melt solidifies partially when it flows down on an oblique plate cooled from bottom by counter flowing water. Columnar dendrites are continuously formed on the plate wall. Because of the forced convection, these dendrites are sheared off into equiaxed/fragmented grains and then washed away continuously by producing semisolid slurry at plate exit. Plate cooling rate provides required extent/amount of solidification whereas plate length enables necessary shear for producing semisolid slurry of desired quality. Slurry obtained is solidified in metal mould to produce semisolid-cast billets of desired microstructure. Furthermore, semisolid-cast billets are also heat-treated to improve surface quality. Microstructures of both semisolid-cast and heat-treated billets are compared. The effects of plate length and plate cooling rate on solidification and microstructure of billets produced by using oblique plate are illustrated. Three different plate lengths (200 mm, 250 mm, 300 mm) associated with three different heat transfer coefficients (1000, 2000 and 2500 W/(m2？K)) are involved. Plate length of 250 mm with heat transfer coefficient of 2000 W/(m2？K) gives fine and globular microstructures and is the optimum as there is absolutely no possibility of sticking of slurry to plate wall.
Key words: aluminum alloy; oblique plate; slurry; microstructure; plate length; plate cooling rate