1989 Volume 75 Issue 2 Pages 298-305
A study has been made on the microstructure and the corrosion behavior of the intermetallic layer of the Zn-Al alloy coating by immersing the conventionally galvanized steel wire in a Zn-Al alloy bath containing 3 to 10 mass% aluminum.
(1) The Zn-Al alloy coating by the double hot-dip process has duplex coating layers. The outer coating layer has the same chemical composition as the alloy bath and the intermetallic layer, which is formed by the diffusion of aluminum from the alloy bath into the Zn-Fe intermetallic layers of the galvanized wire, has a higher content, i. e., approximately 30 mass%, of aluminum than the alloy bath.
(2) The microstructure of the intermetallic layer of the Zn-Al alloy coating consists of the Zn-Al alloy matrix of the quasi-eutectoid phase and the fine, plate-like precipitates of Fe4Al13 containing some amount of zinc.
(3) The intermetallic layer of the Zn-Al alloy coating exhibits such good drawability that the total reduction in area by drawing can be increased to over 80.9% without any crack occurrence.
(4) The first rusting time of Zn-Al alloy coated steel wire in the salt spray test is over four times longer than that of galvanized wire, and the high corrosion resistance is unchanged after drawing.