Simultaneous phosphatizing of steel, galvanized steel, and aluminum

Development of the Process of Passivation of Zinc Surfaces in Molybdate-Containing Solutions

“…In order to eliminate this drawback, a small amount of nickel ions was introduced into the solution, which, as is known, have a beneficial effect on the adhesion of conversion coatings (phosphating and etc.) [12,13]. It turned out that in the presence of nickel ions (in the form of NiSO4•6H2O) in the solution of 0.22-1.12 g/l, the coatings formed in them cease to smear, and their deep black color is not disturbed.…”

Deposition of zinc–zinc phosphate composite coatings on aluminium by cathodic electrochemical treatment

“…Among the non-ferrous metals, deposition of zinc phosphate coatings on Al and its alloys assumes significance in the following respects: (i) the materials of construction of automotive chassis and other parts are being changed from traditional steel and Zn/Zn alloy coated steels to Al alloys to achieve a better fuel efficiency and reduced CO 2 emission; (ii) the conventional chromate or chromium phosphate conversion coatings on Al/Al alloys are being phased out due to the toxicity and carcinogenic nature of Cr(VI) compounds used in these processes [13][14][15]; and (iii) the need to develop processes that can successfully deposit phosphate coatings on a variety of metal substrates without much specificity to the type of surface being treated [16]. In this perspective, the objective of the present study is to explore cathodic electrochemical treatment as an energy efficient and eco-friendly method to deposit zinc-zinc phosphate composite coatings on Al and to evaluate their characteristic properties and corrosion resistance.…”

On the Mechanism of Formation of Conversion Titanium-Containing Coatings

“…Modern technologies for painting steel surfaces include the preliminary formation of adhesive conversion coatings in order to ensure adhesion and increase the protective ability of the subsequent paint and varnish coating (PVC). Most often, before steel surfaces are painted, they are phosphated; galvanized and aluminum surfaces are chromated, although they are also phosphated when in the fabricated structure [1][2][3]. The disadvantages of the phosphating and chromating processes are known and have been repeatedly discussed in the literature [4][5][6][7][8][9].…”

“…H2TiF6 + 2H2O ↔ TiO2 + 6HF (3) 3Fe + H2TiF6 + 6H2O → TiO2 + FeO + Fe2O3 + 6HF +4H2 (4) Fe + 2HF + H2O → FeF2•H2O + H2↑ (5) It is assumed that hexafluorotitanic acid is hydrolyzed at pH 4-5 on the surface of the metal to be treated (steel, zinc, or aluminum) with the formation of titanium oxides. These are at first adsorbed on the surface of heavy metals (Ni, Cu, Co, and Cr), which are on a steel substrate during contact and then expand, forming a continuous coating.…”