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LDH-based active protective treatment for aluminum alloys (LAPTA)

Seed-funded project
ZHM News Projekt LAPTA no text

Figure. Layered double hydroxide (LDH) grown during electrophoretic synthesis at room temperature. Photo: HZG/M. Zheludkevich

The significant demands for “green” aircrafts following the latest European guidelines have set new challenges in the selection of materials and processes in aeronautic industry. Relevant breakthroughs in new protective systems free of toxic chromates have been done in recent years, particularly for 2xxx series aluminum alloys such as AA2024, widely used in aeronautic industry. However, the active corrosion protection performance of the chromate-free conversion coatings is still below the acceptance level.

In frame of this project we have performed a proof of concept for novel LDH (layered double hydroxide)-based conversion treatment, which could meet requirements of aeronautical industry and could be formed under ambient conditions (atmospheric pressure and temperature). The LDH conversion layers were recently demonstrated to provide a possibility to be loaded with environmentally friendly corrosion inhibitors ensuring an important active corrosion protection effect. The fundamental understanding of the treatment parameters (e.g. bath concentration, time, temperature) on the resulting LDH coatings was done.

Within the LAPTA project it was shown, that LDH can be grown at room temperature during electrostimulated treatment conditions (Figure), while for reasonable crystallinity of LDH nanocontainers as a result of hydrothermal growth, a temperature of 95°C is required.

As a next step of this work, the functionalization of grown LDH with “green” environmentally friendly corrosion inhibitors is planned. This work will be done in order to replace Cr(VI)-based treatments, which are banned for most of the industrial application due to their toxicity. LDH-based pre-treatment seems very promising for this purpose and subcontracting of HZG by Airbus in frame of Lufo COVER project started in 2019, confirms this. The collaboration shows the great interest to LDH based conversion treatments and further continuation of the performed work within this ZHM project.