This invention relates to an aqueous solution and a method for preparing an organic protective coating on a Cr(lll) conversion layer which is localized on (anodized) aluminium (alloy) to enhance corrosion protection. The compostion is an aqueous solution which contains water, an organic film forming agent and a corrosion inhibitor, wherein the corrosion inhibitor comprises or consists of at least one 2‐arylriazole. According to the method of the present invention, the composition is used for post‐treating of a Cr(lll) conversion layer on (anodized) aluminium (alloy). The invention further provides a modfied Cr(III) conversion coating on (anodized) aluminium (alloy), which is producible or produced with the inventive method. The modified Cr(III) conversion coating according to the invention shows excellent corrosion protection, paint adhesion and electrical resistivity.