Modificaciones de la microestructura y la capa pasiva de la aleación 2024-T3 Al-Cu durante una limpieza química empleada en la industria aeroespacial

Abstract

A standard surface pretreatment for 2024-T3 Al-Cu alloy prior to the generation of chemical conversion coatings in the aerospace sector have been investigated. These pretreatments influence the alloy phases, which play a key role in the development of new eco-friendly chromium-free conversion coatings, but also in the susceptibility to localized corrosion in chloride medium. The complete pretreatment consists of two alkaline step and another acid step. Scanning Electron Microscopy revealed that after the complete pretreatment, Al(Cu,Mg) phases were partially or totally removed through dealloying with their subsequent copper enrichment, while only the aluminum matrix surrounding the Al(Cu,Fe,Mn,Si) phases was slightly attacked. Electrochemical analysis revealed the turn to cathodic character of Al(Cu,Mg) phases that still remain on the surface, while the Al(Cu,Fe,Mn,Si) phases have a higher corrosion potential than the aluminum matrix. Conversely, none of these phases were affected when only alkaline steps were employed. Identified the corrosion processes that take place in the different phases when the alloy is treated with a surface pretreatment, it is possible to design alternative Cr-free protective process.