Corrosion protection medium for aluminium@ surfaces - process for making corrosion protecting layers on aluminium

摘要

An anti-corroson medium for protecting Al and its alloys contains (%wt.) a metal (esp. K) permeanganate 0.1-30; free or complexed fluoride ions (esp. NaF or NaBF4) 0.001-5; at leat one bath accelerator (esp. acids or salts such as ferricyanide, molybdate, or phosphate) 0.1-2; with the rest being water and the soln. having pH in the range 0-6.5. Treatment conditions are 5-100 deg.C, 10 sec. to 60 mins. and the soln. may be sprayed on, brushed on or the items merely dipped. USE/ADVANTAGE - Method does not suffer from the toxic and ecological problems associated with the use of Cr, nor is it multistage or laborious. In an example, sheet of Al (99.5, Pechiney) was pretreated by degreasing in mild alkali, pickling in 15% NaOH, then complex building in 0.5% Na gluconate at 50 deg.C, and finally deoxidised in 15% HNO3. Just before dipping in the soln. according to the invention the sheet was placed in 65% HNO3 for 2 mins., then immersed in a soln. contg. (%wt.) KMnO4 0.6; K2Fe (III) (CN)6 0.9, and NaBF4 1, the rest being water and the pH 2. After rinsing and drying the protected sheet was subjected to the salt mist spray test. No corrosion spots were discernible after 1008 hr.