Study on Phosphating Pretreatment and Electrophoretic Properties of Hot-Based Zn-Al-Mg Steel Plate

Abstract

The coating and corrosion resistance of hot-based zinc-aluminium-magnesium steel sheet was investigated by means of SEM，XRD，film weight，film thickness，roughness，corrosion resistance，adhesion，stone resistance，water resistance and other comprehensive testing methods，taking the coating performance of hot-rolled pickling plate after electrogalvanizing as a comparison index.Results showed that the pretreatment performance of hot-based zinc-aluminium-magnesium material was equivalent to that of electrogalvanizing material.The coverage rate，particle size，film weight and surface ratio of the phosphating film could meet the quality requirements of the automobile factory.The appearance，adhesion，stone strike resistance and water resistance of the electrophoretic paint film were consistent with those of the electroplated zinc material.The corrosion resistance of hot-based zinc-aluminium-magnesium and its electrophoretic coating was significantly better than that of the hot-rolled pickling plate electrogalvanizing material.After 1 000 h of neutral salt spray corrosion，the bare hot-based zinc-aluminiummagnesium plate did not show red rust，whereas the hot-rolled pickling plate electrogalvanized material showed about 10%of the area of red rust in 336 h.Besides，the stroke × expansion width of the hot-rolled pickling plates after electrogalvanizing was larger than 4 times that of hot-based zinc aluminum magnesium steel plate after electrophoresis.

Keywords

• hot-based zinc aluminum magnesium|electrogalvanizing|pickling plate|phosphating pretreatment|electrophoresis；adhesion|stone strike resistance|water resistance|neutral salt spray test