PREPARATION OF SILICA GLASS COATING AND THE EFFECT OF THE COATING ON THE UNDERCOOLING OF AL-12.5-PERCENT-SI ALLOY

The factors influencing the preparation of silica glass coating on the brass substrate and the effect of coating on the undercooling and the structure of Al-12.5%Si alloy have been investigated. It is shown tha t a uniform sel-gel coating can be formed on the brass substrate when the molar ratios of H2O and ethanol to TEOS are higher than 7-8, the m olar concentration of HCl in the sel is lower than 6 x 10(-4) and the withdrawal rare of the brass substrate from the sel is lower than 5 mm /s. The temperature for changing sel-gel coating to glass coating is 3 60 degrees C. The effects of silica glass coating on the degree of und ercooling and the structure of Al-12.5%Si alloy depend on the melt sta te. The silica glass coating does not influence the undercooling and s tructure of alloys with lower undercooling tendency; while this coatin g can gain the undercooling and refine the structure of the alloys wit h higher undercooling tendency.