CPC C23C 2/12 (2013.01) [C23C 2/06 (2013.01); C23C 2/14 (2013.01); Y10T 428/12021 (2015.01); Y10T 428/12028 (2015.01)] | 10 Claims |
1. A method for forming a coating of a corrosion resistant Al—Zn—Si—Mg alloy on a metal strip, the method comprising:
(a) passing the metal strip through a molten bath of the Al—Zn—Si—Mg alloy and forming a coating of the alloy on one or both surfaces of the metal strip, wherein the alloy contains 40-65 wt. % Al, 35-50 wt. % Zn, 1.0-3 wt. % Si, 1.5-2.5 wt. % Mg, and optionally other elements in amounts of less than 0.5 wt. % for each other element,
(b) solidifying the coating on the metal strip and forming a solidified coating having a microstructure that comprises dendrites of Al-rich alpha phase and interdendritic channels of Zn-rich eutectic phase mixture extending from the metal strip, wherein particles of Mg2Si phase are positioned in the interdendritic channels in the solidified coating, and
(c) controlling the cooling rate during coating solidification step (b) such that the particles of Mg2Si phase in the interdendritic channels in the solidified coating block corrosion along the interdendritic channels,
wherein greater than 60% of the interdendritic channels are blocked by particles of Mg2Si phase, and
wherein the solidified coating has an overlay thickness greater than 5 μm and less than 30 μm.
|