to form a double layer undercoat of enhanced characteristics it is usually desirable that the composite have a base layer that is more noble than its covering layer but less noble than the substrate metal e g steel the method of applying the undercoating will in general be determined by the economy of application for the particular undercoating selected for example with the zinc iron undercoatings such may be applied by usual zinc application to an iron substrate followed by annealing on the other hand the preferred zinc nickel undercoatings may be applied by electrolytic application including deposition technique relying on subsequent heating for alloying electroless deposition of undercoatings is also contemplated most typically regardless of the means of application the metallic undercoating layer will be present on the metal substrate in an amount of less than about 25 microns thickness greater amounts can be uneconomical as well as leading to thick coatings which may be deleteriously brittle for best economy coupled with highly desirable corrosion resistance such metallic undercoating layer will advantageously be present in a thickness on the metal substrate of below about 15 microns and often on the order of about 10 microns or less on the other hand undercoats of about 0 1 micron thickness or so are generally insufficient for providing outstanding enhancement in corrosion resistance therefore the metallic undercoating will be present in a thickness of at least about 0 2 micron and more typically in at least about 0 3 micron thickness such that there will most preferably be present a metallic undercoat layer of from about 0 2 to about 2 microns of particular interest as hexavalent chromium containing topcoatings for the present invention are bonding coatings those that are preferred.