Study On The Black Film Phosphating Process Of Steel

The black phosphating technology as a kind of an important surface treatment processfor steel protection and decoration is more and more extensive attention in machinery andother industries. Especially the black phosphating coating can not impact the precision ofparts and can reduce diffuse reflectance of the instrument’s inner surface.The paper first reviews the black phosphating coating processes research significance,international research present condition as well as the classification and basic principle of theprocess; It also analyzes the main influence factors of the black phosphating coatingprocesses.Then, it Summarizes the advantages and disadvantages of existing formulation bychecking them. Finally, it acquires a kind of possible experiment based on this study and thecorresponding experiment is discussed.This study adopted Q235steel as the base material and used two-step method, an effectiveprocess of black phosphating was studied by blackening at room temperature first and thenphosphating at medium temperature. The roles of main components of blackening andphosphating solutions as well as the influence of post-treatments such as saponification andoil seal on the surface of Q235steel were investigated. Meanwhile, the microstructure of theblackening film, the black phosphating coating and the black phosphating coating after posttreatments are observed by scanning electronic Microscopy （SEM）. It has been showed thatSbCl₃plays a key role for the blackness of the steel surface, FeCl3,（NH₄）₆Mo₇O₂₄andC₄H₆O₆also have different roles, the optimum blackening time is3.5⁵min; Theconcentration of Zn（H2PO4）2should not exceed9.09%in phosphating solution, there is acertain relationship between Ca（NO₃）₂, Ni（NO3）₂, C₆H₈O₇, H3PO3and the quality of blackphosphating coating; In addition, by saponification, oil seals and other post treatments, thecorrosion time of the black phosphating coating in copper sulfate spot test can be as high as35min.