Corrosion Inhibition of Aluminum and Aluminum Alloys by Soluble Chromates, Chromate Coatings, and Chromate-Free Coatings

A study of the mechanisms of corrosion inhibition of AA2024-T3 by vanadates using the split cell technique

“…Due to the susceptibility to localized corrosion, aluminum alloys for aerospace applications are protected from the aggressive environment using multi-layered coating systems based on the chemistry of chromates [18][19][20][21][22][23][24][25]. It has been shown that the formation of a Cr 3+ monolayer inhibits oxygen and further Cr 6+ reduction [18,[27][28][29][30][31][32].…”

High Strength Al-Alloys: Microstructure, Corrosion and Principles of Protection

“…For high strength Al-alloys such as 2xxx and 7xxx series chromate conversion coating (CCC) is still the preferred process. Replacements for chromate-based conversion coatings include a range of treatments based on selfassembled monolayers, sol-gel chemistries, Ti/Z oxyfluorides, rare earth, cobalt, vanadates, molybdates and permanganate processes (Twite and Bierwagen 1998;Kendig and Buchheit 2003). These processes are widely developed for chemically pretreated surfaces that have nearly all the IM particles removed and are not specifically designed to address electrochemical and compositional variations found for a heterogeneous surface such as when the IM phases are present.…”

“…So the simplest improvement to inhibitor design is to increase the functionality by finding compounds which play both a cationic and anionic inhibitive role. A large range of cations including Zn, Ca, and rare earths (Bohm, McMurray et al 2001;Du, Damron et al 2001;Kendig and Buchheit 2003;Taylor and Chambers 2008;Muster, Hughes et al 2009) have been combined with either organic (Osborne, Blohowiak et al 2001;Sinko 2001) (Voevodin, Balbyshev et al 2003;Khramov, Voevodin et al 2004;Blin, Koutsoukos et al 2007;Taylor and Chambers 2008;Muster, Hughes et al 2009) or inorganic (oxyanions, carbonates, phosphates, phosphites, nitrates, nitrites, silicate (Bohm, McMurray et al 2001;Sinko 2001;Blin, Koutsoukos et al 2007;Taylor and Chambers 2008)) compounds. Anions with dual functionality, such as some of the transition metal oxyanions which are both oxidants and anions, have been investigated extensively.…”

Chromate replacement: what does the future hold?

“…17 The remarkable corrosion resistance of chromates is persistent over a very wide range of pH and electrolyte concentrations; 18,19 a feature unable to be matched by alternative inhibiting compounds to date, most having finite operating pH and minimum concentration requirements. [20][21][22] The mechanism of corrosion inhibition from chromates, irrespective of chromates being known utilized for many decades prior, is something that has really only been understood in more contemporary times.…”