Preparation of silica glass coating and the effect of the coating on the undercooling of Al-12.5%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 that 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 molar concentration of HC1 in the sel is lower than 6 × 10 ~4 and the withdrawal rate of the brass substrate from the sel is lower than 5 mm/s. The temperature for changing sel-gel coating to glass coating is 360℃ . The effects of silica glass coating on the degree of undercooling and the structure of Al-12.5 % Si alloy depend on the melt state. The silica glass coating does not influence the undercooling and structure of alloys with lower undercooling tendency; while this coating can gain the undercooling and refine the structure of the alloys with higher undercooling tendency.