Design Of Sectional Cooling Slope Device And Study On Preparing Processing Of Semi-solid Slurry Of Aluminum Alloy By The Device

Sectional cooling slope device was designed and used to connect semi-solid rehoforming process and die casting process. The semi-solid slurry of A356aluminium alloy was prepared by the device, then the refinement and spheroidizing mechanism primary α-Al was explored. The microstructure and grain size of primary a-Al were investigated on the influences including the material of up/down cooling slope plate, the angle of up/down cooling slope plate, the length of up/down cooling slope plate, the pouring temperature of molten aluminium alloy and heat preservation. The solid fraction fs of semi-solid slurry, average equivalent diameter and roundness F of the primary a-Al were analyzed and calculated.The overheated molten aluminium alloy is poured on the surface of up cooling slope plate, then is chilled sharply by the cooling plate. So heterogeneous nucleation generates on the surface and crystal nucleus grow up gradually. The grains fall out of the surface under gravity and impact of the metal fluid. When the semi-solid slurry pour into the down cooling slope plate, the grains ripen into more-or-less spheroidal shape by weak chilling action of the down cooling plate. Finally, the primary phase grows in an uniform manner.Semi-solid primary α-Al which are prepared by the material quality of steel/graphite slope plate,are more small,round and homogeneous than that applys single slope plate. Meanwhile,In the preparation of slurry, the residual quantity of semi-solid slurry which is prepared by steel/graphite slope plate is less than that in graphite/steel slope plate.and is convenient to clean.Increasing the angle of slope plate,the impact of corrosion and crash are strengthened,but the flowing time is reduced,so that the cooling effect of slope plate to slurry is increased.Dereasing angle of up plate,and increasing angle of down plate,ensure the strong cooling function of slope plate to slurry,and the impact of corrosion and crash would be not weaked. Increasing effective cooling length of slope plate,can not only increase the flowing time of slurry on slope plate,but also enhance the cooling and cut faction.While the length of plate increases till a value,the solid phase fraction of slurry can increase,so that the viscosity of slurry increases and slurry is difficult to flow, finally appear crusting phenomenon of slurry on slope plate.In the preparation of slurry, semi-solid microstructure which holds in graphite crucibles is better round than that without holding, but grains tend to grow up.The holding process actually is the growth process of primary α-Al, therefore the holding time would not be too long.Research shows that:when the material of up/down cooling plate are steel and graphite, the angle of up/down cooling plate are30°nd50°, pouring temperature is670℃, the valid length of up/down cooling plate are250mm/250-150mm, the size of primary α-Al phase was fine, rounding and homogeneous, its average equivalent diameter is44.7μm, its roundness is0.69, the solid fraction is63.9%.