| Hot dip galvanizing technology is the mainly anti-corrosion method for steel products.In practical applications,hot dip galvanizing equipments are usually in short life,which leads to frequent maintenance and replacement.Through some research and practice,spraying a ceramic-metal protective coating on the consumable parts of galvanizing equipments will significantly improve the above problems.However,the bonding metal layer in the protective coating is relatively low cohesion,once it drops off,it will result in the protective coating failure.Thus,the research on the mechanism of the bonding metal and liquid zinc is particularly important.In this paper,four kinds of bonding metal,metal Ni,metal Co,metal Mo and metal Cr,were used to study the direct effect with liquid zinc.Then four kinds of metal powder were sprayed onto the 304 stainless steel substrate by plasma spraying.Later,in order to study the mechanism of metal coatings and liquid zinc,the workpieces were immersed into molten zinc at 530? for a period of time to simulate the actual service of the industrial galvanizing equipments.The morphology of the corrosion layer between the substrate and solidified zinc was observed by scanning electron microscopy.And the new phases formed on the corrosion layer were analyzed by X-ray diffraction.Through the theoretical analysis and experimental verification,it can conclude that the corrosion mechanism of metal Ni and metal Co in liquid zinc is similar,containing chemical reaction corrosion and reaction diffusion corrosion,and finally the two kinds of metal are all failed in the form of uniform erosion.In order to study the corrosion rate,the corrosion rate test is finished.The results show that the corrosion rate of pure metal Ni in liquid zinc is 0.00604g/(cm2·h),and 0.00424g/(cm2·h)of pure metal Co.The corrosion mechanism of pure metal Mo in liquid zinc contains chemical reaction corrosion and reaction diffusion corrosion at the same time,which presents the formation of a new phase MoZn22.Secondly,it also shows the corrosion along the surface defects.The corrosion mechanism of metal Mo coating is similar to that of pure metal Mo.The mechanism of pure metal Cr and metal Cr coating is similar,which also presents corrosion along the surface defects,and then the defects expand.The penetrating cracks form ultimately,and the material drops off. |
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