Process for surface-treating an aluminum-containing metal

A process for surface-treating an aluminum-containing metal material, comprising the steps of:

• chemically etching at least a portion of a surface of an aluminum-containing metal material to an extent such that the material exhibits a reduction in weight of 0.02 to 20 g/m2;
• applying a chemical conversion treatment to the chemically etched surface of the aluminum-containing metal material with a chemical conversion treating liquid containing at least one member selected from the group consisting of zirconium phosphate and titanium phosphate, to form a first protective layer;
• and
• forming a second protective layer containing a hydrophilic resin cross-linked with a cross-linking agent on the first protective layer,
• wherein the cross-linking agent comprises at least one member selected from chromium compounds, zirconium compounds and titanium compounds;
• the cross-linked hydrophilic resin contained in the second protective layer comprises (a) non-cross-linked hydrophilic functional groups selected from the group consisting of primary amino groups, secondary amino groups, tertiary amino groups, quaternary ammonium salt groups, an amide group, a carboxyl group, a sulfonic acid group, phosphoric acid group and a hydroxyl group, and being non-reactive to the cross-linking agent;
• and (b) reactive functional groups being reactive to the cross-linking agent, selected from the group consisting of an amide group, a hydroxyl group and a carboxyl group, and being different from the hydrophilic functional groups (a);
• and at least a portion of the reactive functional groups (b) is cross-linked with the cross-linking agent.