Surface modifying method for galvanized steel sheet
A galvanized steel sheet according to one aspect of the present invention comprises: a base steel sheet; and a Zn—Al—Mg-based plating layer provided on at least one surface of the base steel sheet, wherein the Zn—Al—Mg-based plating layer may include a surface modified region enriched with cerium (Ce) on a surface layer side of the Zn—Al—Mg-based plating layer.
1 . A surface modifying method for a galvanized steel sheet, comprising:
a first step of preparing a galvanized steel sheet having a Zn—Al—Mg-based plating layer on at least one surface of a base steel sheet;
a second step of preparing an aqueous cerium nitrate solution by dissolving 15 to 25 g of cerium nitrate per 1000 ml of water (H 2 O) and adjusting the pH to 3.2 to 3.8 by titrating with nitric acid (HNO 3 );
a third step of immersing the galvanized steel sheet in the aqueous cerium nitrate solution; and
a fourth step of washing and drying the galvanized steel sheet that has been immersed in the aqueous cerium nitrate solution.
2 . The surface modifying method for a galvanized steel sheet of claim 1 , wherein the first step of preparing the galvanized steel sheet comprises:
preparing a Zn—Al—Mg-based plating bath; and
forming a plating layer by immersing the base steel sheet in the Zn—Al—Mg-based plating bath;
wherein the Zn—Al—Mg-based plating bath comprises 0.1 to 16 wt % magnesium (Mg), 0.1 to 12 wt % aluminum (Al), the remainder zinc (Zn) and unavoidable impurities; and
wherein the cerium (Ce) content in the Zn—Al—Mg-based plating bath is 0.01 wt % or less, including 0 wt %.
3 . The surface modifying method for a galvanized steel sheet of claim 1 , wherein the third step of immersing the galvanized steel sheet in the aqueous cerium nitrate solution is performed at a temperature of 20 to 80° C., and wherein the immersion time is 10 to 150 seconds.