THE ROLE OF SOLIDUS VELOCITY IN THE FEEDING-BEHAVIOR OF AL-7SI-0.3MG ALLOY PLATE CASTINGS

The present study attempts to investigate systematically the combined influence of feeder size and casting length on the feeding behaviour of Al7Si0.3Mg alloy. The castings were examined by X-ray radiography and density measurement to determine their feeding efficiency. During solidification, thermal data were taken to analyse the thermal gradient G, the local solidification time t, the ratio G/t and the solidus velocity VS. The purpose was to characterize the significance of the solidus velocity compared with other parameters in predicting the formation of porosity. The solidus velocity is proposed as a useful parameter to characterize the feeding of Al7Si0.3Mg alloy in which measurement of the thermal gradient at the final stage of solidification becomes difficult. Both riser size and length of casting exert a large influence on the solidus velocity from the free end to the riser. The solidus velocity is slow at the free end; it increases to a maximum at a position about one-third of the distance from the riser end and then slows down again when approaching the riser. Good prediction of VS on porosity content is obtained in this experiment. © 1990.