抄録
Various methods for pretreating Mg-alloy plates have been evaluated. Chemically treated plates were more adhesive to enamels than anodically oxidized. Neither of these treatments, however, could prevent the samples from growing black in firing of frit. A new pretreatment called water glass method has been proposed, which provides better substrates for the abhesion of lead enamel and also for preventing growing-black. Several pretreatments for Mg-alloy plates: no-treatment (except pickling with 10% HNO3 at room temperature), Dow 15 method, De Long method and water glass method were applied to find out the cause for growing-black of enamel and also to examine the adhesion of some low melting frits on the Mg-alloy plates. Lead enamel treated by water glass method showed a high adhesive strength in the bending test and the finish of enamelled surface was glossy and transparent. Lead enamels treated by Dow 15 and De Long methods, however, showed poorer adhesion than that by water glass method, and the finish of enamelled surface was black. Phosphate and antimonate enamels, on the other hand, were of the lowest strength of adhesion for all these pretreatments. The best adhesion for the lead enamel was obtained when drying of the slip was done at 50°C for 50min and firing at 540°C for 10sec. Growing-black of enamels was attributed to the deposition of metallic lead in the boundary surface between frit and Mg substrate, that is caused by the reduction of lead oxide in the frit by metallic magnesium in the plates. The metallic lead deposition was found to reduce the adhesive strength of enamels.
