Formation of a cerium-based conversion coating on AA2024: relationship with the microstructure

Chromate replacement: what does the future hold?

“…95 Buchheit et al 103 used Zn-Al layered double hydroxides (LDHs) as containers for inhibiting decavanadate ions (V 10 O 28 6-), within epoxy coatings upon AA2024-T3. It was observed that firstly, decavanadate ions Several studies demonstrated the presence of Cr(VI) within the conversion coating 45,46 Suspected to be carcinogenic 50 RE-based (Ce or La) AA2024-T3 57,58,63 Mainly works as cathodic inhibitors, precipitation of Ce-oxide on cathodic sites, induced by the local pH increase Vulnerability of RE market as mainly dominated by Chinese production 66,67 Galvanized steel 62 Only minor improvement in pitting potential and corrosion current was noted 56,65 Vanadate-based AA2024-T3 zinc carbon steel 69 Adsorption of inhibitor on cathodic sites (intermetallic particles in the case of AA2024-T3) and stabilization of passive film. Inhibition of oxygen reduction reaction [20][21][22]70 Do not meet environmental and health restrictions as Vanadium and its compounds were proven to be carcinogenic [72][73][74] Li-containing Only tested on AA2024-T3 Good barrier properties provided by both systems Organic: effective inhibitor is still needed to achieve good corrosion resistance Nanocomposites: higher density of inhibitor can be loaded into the system Nanocomposites: cost towards implementation could be too important 99,100 Phosphate-based Steel carbon steel Al alloys zinc were controllably released from the LDH containers and also that the aggressive chloride ions were also entrapped within such containers.…”

“…3). [55][56][57][58] or lanthanum nitrate (La(NO 3 ) 3 ) 59,60 ) tend to form Cerium or Lanthanum oxides/hydroxides at a pH > 10, and therefore could inhibit cathodic reactions on corroding surfaces. Indeed, rare-earth salts were able to inhibit the corrosion of several systems such as Zn, galvanized steel, Mg, or Al alloys and successfully integrated into primers or conversion coatings.…”

“…Indeed, rare-earth salts were able to inhibit the corrosion of several systems such as Zn, galvanized steel, Mg, or Al alloys and successfully integrated into primers or conversion coatings. [56][57][58][61][62][63][64] However, the rareearth-based oxides could dissolve in an acidic environment and therefore making this rare-earth-based surface layer less stable or durable, compared to the Cr 2 O 3 layer form using hexavalent chromium. In addition, several studies performed on a coated Al alloy AA2024-T3 reported minor improvement in pitting potential and corrosion current, calling into question the efficacy of Cebased conversion coatings.…”

Multidimensional electrochemical imaging in materials science

“…In the past decade many KFM studies have also been conducted on a broad range of topics in corrosion science, including research on the corrosion behavior of steel [136][137][138][139][140][141][142][143][144], Al [143], Cu [145][146][147][148], Zn [143,144,[149][150][151][152], alloys based on Al-Mg [153][154][155][156][157][158][159][160][161][162][163][164] and Ti [165], on corrosion protection with rare-earth elements [166] and other inhibitors [167][168][169][170], the effect of conversion coatings [171][172][173][174][175][176], and the effects of heat treatment on material properties [177][178][179]. Yamawaki et al …”

Corrosion Resistance of Cerium-Conversion Coated AZ31 Magnesium Alloys in Cerium Nitrate Solutions

“…12,13) Furthermore, cerium conversion coatings on aluminum alloys have studied extensively. [14][15][16][17][18][19][20][21][22] In contrast, cerium conversion coating treatments for magnesium alloys are less well studied.…”