method for manufacture of anticorrosive coatings on aluminum alloys and preserved products.

摘要

This invention provides an aluminum alloy conversion coating composition and a process for protecting aluminum alloys, especially the alloys having greater than 1.0% Cu with a conversion coating. The coating is placed on the aluminum alloy in a multi-step process. In a first step the alloy is treated with a composition having as essential ingredients aluminum nitrate and an alkali metal nitrate, in a second step the nitrate treated alloy is treated with an alkali metal permanganate composition and in the final step the alloy is treated with an alkali metal silicate composition. Also, alternatively, the first step composition is an alkali metal permanganate-borax composition, the second step composition is a composition containing phosphate, aluminum and nitrate ions, the third step composition is an alkali metal permanganate composition and the fourth step composition is an alkali metal silicate composition. The aluminum conversion coatings of this invention are provided without the need of using toxic chromium compounds.