“…Different non-chromate conversion coatings (NCCC) are obtained from aqueous solutions of rare earths with or without the presence of activator agents [17], phosphate conversion coatings or coatings obtained by deposition of conducting polymers. Films produced from fluorotitanic or fluorozirconic acids, cobalt salts, and phosphate permanganate coatings are available, but they are less effective than the previous traditional chromate treatments [18][19][20][21].…”