摘要:
Zn--Cr alloy plated steel sheets have excellent corrosion resistance. It has now been found that the phase structures of Zn--Cr alloy platings are such that they comprise yet to be known phases .eta.x, .delta.x and .GAMMA.x. Furthermore, these phases when taken either singly or with two or more phases being mixed together, exhibit the following characteristics (1)-(6). The characteristics of the respective phases are also identified below.______________________________________(1) .eta.x Resistance to cosmetic corrosion(2) .GAMMA.x Formability(3) .eta.x + .delta.x Chipping resistance(4) .eta.x + .GAMMA.x Corrosion resistance in the as-formed state(5) .delta.x + .GAMMA.x Water resistant secondary adherence of coating(6) .eta.x + .delta.x + .GAMMA.x Perforation corrosion resistance.eta.x: Hexagonal crystal a = 2.66-2.74 .ANG. c = 4.61-4.95 .ANG..delta.x: Hexagonal crystal a = 2.72-2.78 .ANG. c = 4.43-4.60 .ANG..GAMMA.x: Cubic crystal a = 3.00-3.06 .ANG.______________________________________