Preparation and corrosion resistance of titanium–zirconium–cerium based conversion coating on 6061 aluminum alloy

Abstract

This paper aims to develop a chromium‐free chemical conversion coating with good corrosion resistance. A novel chemical conversion coating was prepared on 6061 aluminum alloy by dipping in the treatment solution containing titanium/zirconium based‐ions and sodium metaphosphate and cerium nitrate hexahydrate as additives. The morphology and composition of the conversion coatings were observed by scanning electron microscopy and energy dispersive X‐ray spectroscopy. The microarea structure of conversion coatings at different formation stages was analyzed by electron probe microanalyzer. The electrochemical polarization curve revealed that the corrosion potential of the conversion coating was −0.577 V and the corrosion current density was 0.1148 μA/cm2. The equivalent circuit fitted by AC impedance showed that the film resistance reaches 68,140 Ω. The formation of coating preferentially grows on the Al (Fe) Si intermetallic to form oxides of Ti and Zr; then TiO2 formed by a higher concentration of Ti4+ gradually covered ZrO2. Ce3+ could adsorb on the intermetallic compound, the hydrolysis of which causes the local pH of the solution to decrease and promotes the aluminum alloy dissolved.

Effects of environmental factors on corrosion behavior of aluminum

“…Chlorine ions are known as a major element causing pitting corrosion by chemical attack of the passive film on the aluminum surface. [18][19][20][21] Particularly, corrosion of aluminum may be further promoted in summer due to the hot and humid environment. [22] Also, Cl − ions on the surface of the heat exchanger may be concentrated, leading to a serious corrosion phenomenon.…”

Formation and corrosion resistance of a novel Co–Ti–Mo composite chromium‐free chemical conversion coating on LY12 aluminum alloy

“…Figure 4 exhibits the potentiodynamic polarization curves of Al alloy matrix, CoTiCC (Co 2 SO 4 : 2.0 g/L and H 2 TiF 6 : 1.5 ml/L) and CoTiMoCC (Co 2 SO 4 : 2.0 g/L, H 2 TiF 6 : 1.5 ml/L, and Na 2 MoO 4 : 1.0 g/L) in a neutral 3.5 wt% NaCl solution. The shape of polarization curves is similar to each other, and the relevant values of corrosion potential (E corr ) and corrosion current density (i corr ) are displayed in the inset [22]. Generally speaking, E corr is a thermodynamic parameter to characterize corrosion susceptibility.…”

“…However, the distinction of the dropping time between the Na 2 MoO 4 content of 1.0 and 2.5 g/L is insignificant, and only 7 s. As a result, based on the economic benefits and the improvement of corrosion resistance, the most appropriate addition amount is 1.0 g/L. [22] Generally speaking, E corr is a thermodynamic parameter to characterize corrosion susceptibility. Obviously, CoTiMoCC demonstrates a nobler E corr value than the Al alloy matrix and CoTiCC and thus has a more thermodynamically steady system than the other.…”

“…LY12 aluminum alloy contains an Al-rich matrix and a certain amount of intermetallic compounds, such as Mg 2 Si and Al 2 CuMg. [22,23] Owing to the chemical potential difference, the Al-rich matrix is used as the micro anode, while the intermetallic compounds are used as the micro cathode. Usually, in an electrochemical corrosion system, the metal dissolution reaction occurs in the micro anode, whereas the H evolution reaction together with the oxygen absorption reaction occurs in the micro cathode, as shown in Figure 10b.…”

Surface treatment and adhesion strength of aluminum foil for lithium‐ion battery package

“…8 Thus, a variety of chromate-free and environmentally friendly conversion coatings have been developed, such as phosphate/permanganate conversion coating, 9 molybdate conversion coating, 10 silicate conversion coating, 6 zirconium/titanium conversion coating, [11][12][13] and cerium (Ce) conversion coating. [14][15][16][17][18] Among these coatings, Ce conversion coating is a promising alternative to Cr (VI) conversion coating due to its unique properties such as environmental friendliness, high adhesive strength to the substrate, and excellent corrosion resistance. 19,20 In recent years, considerable efforts have been devoted to improving the corrosion resistance of Ce-based coatings on metal substrates.…”