An experimental study of porosity formation in long-freezing-range A206 alloy plate and taper castings

Abstract

Experiments have been carried out in order to allow the porosity content to be predicted in long- freezing-range A206 alloy (Al-4.5 wt% Cu-0.4 wt% Mn-0.3 wt% Mg-0.2 wt% Ti) plate and taper castings with systematic variations of riser size and length. A monogram with a plot of amount of porosity as the ordinate, freezing ratio (FR) as the abscissa and volume ratio (VR) as the third variable was established in order to determine porosity formation as a function of riser and casting geometries. Accordingly, the amount of porosity tends to decrease with decreasing freezing ratio and with increasing volume ratio. Increasing riser size and placement of taper decrease the amount of porosity through increasing the volume ratio and decreasing the freezing ratio, respectively. In order to produce a sound A206 alloy casting, based on the criterion of amount of porosity, the volume ratio and freezing ratio should obey the relationship VR > 0.4 (FR)^1.5.