STATISTICAL-ANALYSIS OF POROSITY IN AL-9 WT-PERCENT SI-3 WT-PERCENT CU-X ALLOY SYSTEMS

A set of 72 solidification experiments was carried out on Al-9 wt % Si -3 wt % Cu-X alloys, varying the additives (namely, strontium, grain r efiner and other alloying elements), hydrogen level and thermal parame ters in order to obtain a statistical analysis of the resulting porosi ty in such alloy systems. For all the cases studied, it was found that in each case, the smaller sized pores (in terms of pore length or por e area)could be described by an exponential function, while the larger sized pores were distributed in an irregular fashion, ''small'' and ' 'large'' being distinguished by that limiting value of pore length or area at which the average value equalled the standard deviation. Two d ifferent approaches i.e. factorial and regression methods were utilize d to quantify the importance of the parameters controlling the pore si ze and porosity volume fraction. Two main observations were made: (i) hydrogen is the strongest parameter enhancing porosity formation, with the hydrogen-grain refiner, strontium, strontium-titanium and solidus velocity-solidification time interactions being the other parameters that contribute significantly to porosity formation and increase in po re size; (ii) the grain refiner, hydrogen-phosphorus, strontium-magnes ium and iron-phosphorus interaction parameters reduce the porosity, th ough in different magnitudes. The reliability of predicting the observ ed effects by the two methods has been discussed.