The Influence Of Selective Oxidation And Galvannealing Parameters On The Structure And Properties Of DP590 Galvannealed Coatings Layers

Weight-saving design is one of the high priorities for the automotive industry. Some other considerations, such as greater comfort and safety, and at the same time, fuel economy and environmental constraints must be also considered. Among different materials to obtain these goals, dual phase (DP) steels are amongst the most promising candidates. GA coating with its excellent corrosion resistance, coating properties, weldability and advantages of high strength are more and more used in automotive industry. In this paper, the influence of selective oxidation of DP590 on the galvannealing behavior of DP590 was analyzed.SEM, EDS, XPS,60 degree V bending and roughmeter was applied to analyze the effects of dew point and preoxidation-reduction process on the selective oxidation of DP590, what's more, infuence of selective oxidation, galvannealing temperature and time on the suface morphology, cross-sectional structure, inhibition layer and surface roughness of coatings on the DP590 steel was also analyzed.Conclusions can be drawn as follows:(1)Complete coatings can be gained at -50?,-30?,-10?, +10/-50?,+5/-50?etc dew point conditions. When the dew point condition is +10/-50?,the amount of oxides is the smallest largest,while when the dew point condition is the largest.There are Fe-Zn phase in the coatings at-50?,-30?,-10?, +10/-50?,+5/-50?etc dew point conditions.(2)When the subject is in the zinc bath, the morphology oxides on the suface,which would be aluminothermic redued by Al in the zinc bath, which results in difference in the composition at coating/substrate interfacial layer; Prior to galvannealing, Either inhibition layer or oxids at interfacial layer will retard the galvannealing process of DP590; No inhibition layer or oxids was found at interfacial layer(gained at dew point -50?,Al content 0.12%),which is good for galvannealing process.(3)Powdering-resistance property of GA coatings, galvanized at dew point condition -30? and +10/-50? then galvannealed at 500? for 30s is very good, but they are underalloyed; Powdering-resistance property of GA coatings, galvanized at dew point condition -10?,-50? and +5/-50? then galvannealed at 500? for 30s is poor, but they are overalloyed.(4)GACoatings, galvannealed at dew point-50? then galvannealed at 500? for 25s is comprised of 5and ?, phase without ?phase wihich is thought to be optimum-alloyed GA coating,has the good powdering resistance property.