INFILTRATION AND WETTING OF ALUMINA PARTICULATE PREFORMS BY ALUMINUM AND ALUMINUM-MAGNESIUM ALLOYS

The infiltration and wetting of alumina particulates by Al and by Al-M g alloys was studied through pressure infiltration experiments. In the se experiments, a noninvasive capacitance technique was used to determ ine the infiltration front position as a function of time. An unsatura ted slug flow model was used to interpret the infiltration results and determine capillary pressures characteristic of the infiltration proc ess. The characteristic capillary pressures for Al, Al-2Mg, and Al-3Mg at 750 degrees C and Al-2Mg at 850 degrees C were not significantly d ifferent. Therefore, contrary to usual belief, Mg did not significantl y aid the pressure infiltration process. At 750 degrees C, the maximum values of the contact angle calculated from these capillary pressures were 106 deg for Al and 105 deg for Al-2Mg and Al-3Mg. These contact angle values indicate substantial removal of the oxide layer on the su rface of the liquid metal during the infiltration process. The small d ifference in the contact angles indicates that magnesium had little ef fect on the wetting of alumina by aluminum, The small effect of Mg on the wetting may be due to absence of reactive wetting at the infiltrat ion speeds present in the experiments and to partial disruption of the oxide layer on the surface of tile liquid metal during the infiltrati on process.