基板表面锈蚀对热镀锌及锌铁合金化镀层的影响

Effect of substrate surface rust on hot⁃dip galvanized and galvannealed coatings

利用表面局部锈蚀的无间隙原子钢(IF钢)冷轧板,在IWATANI热镀锌模拟器上进行了退火及热镀锌模拟,研究了基板表面锈蚀对退火、热镀锌(GI)与锌铁合金化(GA)镀层的影响。结果表明,在800℃、N_(2)+5%H_(2)的气氛中连续退火之后,锈蚀被还原成晶粒细小、结构疏松、彼此之间存在大量微孔的还原铁。在热镀锌时,还原铁与锌液发生快速扩散,使镀层内出现锌铁合金相,降低了锌液流动性,从而当试样经过气刀时,影响了镀层厚度的控制,使得锈蚀位置的GI镀层局部偏厚。镀层合金化之后,锈蚀位置的GA镀层形貌与正常镀层完全不同,镀层平且厚,最终在GA镀层表面表现为白色斑点缺陷。

Annealing and hot⁃dip galvanizing simulations were conducted on the cold⁃rolled IF steel sheet with localized surfacerust by using IWATANI hot⁃dip galvanizing simulator.Effects of substrate surface rust on annealed,hot⁃dip galvanized(GI)and galvannealed(GA)coatings were studied.The results show that after continuous annealing in an atmosphere of N_(2)+5%H_(2) at 800℃,the rust is reduced to reduced iron with small grains,loose structure and numerous micropores between each other.During hot⁃dip galvanizing,the reduced iron rapidly diffuses with the molten zinc,causing the appearance of a zinc iron alloy phase in the coating and reducing the fluidity of the molten zinc,which further affects the control of the coating thickness when the specimen passes through the air knife,resulting in localized thickening of the GI coating at the rust location.After coating alloying,the morphology of the GA coating at the rust position is completely different from that of the normal coating,that is,the coating is flat and thick,and ultimately shows as white spot defects on the surface of the GA coating.