Mechanical Property Evaluation of Magnesium Rich Primer Coating System Over AA 2024 T-3 Aluminum Alloy by Nano-Inedntation

Abstract

Aluminum alloy is widely used as a major structural material, such as for wing and fuselage, in aerospace industry. Corrosion is the most insidious form of damage to aluminum alloy, which can cause aircraft structure damage and related safety issue. Coating is generally used in industry to protect metal structure. An alternative to present toxic chromium primer coating system, magnesium rich primer (MgRP) has been developed to protect AA 2024 T-3. Studies have demonstrated the anti-corrosion performance of MgRP. However, the interlayer material heterogeneity can affect the mechanical properties of coating such as modulus, hardness and interfacial behavior. In the present study, AA 2024-T3 samples with both chromium primer and magnesium primer coating systems are examined experimentally and computationally. The nanoindentation experiment in combination with finite element analysis (FEA) shows that the mechanical properties of the top coating are not affected by interlayer material heterogeneity under low indentation loading, 10,000 µN. However, if the indentation force is increased to 60,000 µN, delamination could occur at the MgRP. FEA results show the apparent differences in the maximum principal stress value and location in MgRP compared with chromium coating. It is explained by the fact that the larger magnesium particles in MgRP lead to greater stress concentration at the particle boundary. The greater stress induces delamination.