Feeding to castings from a riser in a pasty state

Abstract The amount of porosity and the degree of macrosegregation are measured in Al-4.5wt.%Cu alloy ingots solidified unidirectionally upwards from the chill face. When low melting point liquid metal is added onto the top of solidifying ingots just before the top region becomes in a pasty state, the amount of porosity is smaller and the degree of macrosegregation larger than those in an ingot to which no liquid metal has been added. This is because the addition does not increase the resistance to liquid flow which, in the case of no addition, would come from a capillary force resulting from the surface tension at the top free surface of the interdendritic liquid and prevent the movement of the interdendritic liquid. The amount of porosity and the degree of macrosegregation in the ingots with and without the addition were also computer simulated and are compared with the experimental results.