A method for electroplating a substrate having an aluminum alloy surface comprises: applying a zinc layer onto the aluminum alloy surface; electroplating a first copper layer onto the zinc layer from an alkaline copper electroplating solution; electroplating a second copper layer onto the first copper layer from an acid copper electroplating solution; electroplating a Cu—Sn alloy layer onto the second copper layer from a Cu—Sn electroplating solution; and electroplating a chromium layer onto the Cu—Sn alloy layer from a trivalent chromium solution. The alkaline copper electroplating solution is substantially free of cyanide ion.