A combined experimental and finite element approach for determining mechanical properties of aluminium alloys by nanoindentation

Aluminium alloys for the aerospace industry are often clad by roll-bonded aluminium to improve corrosion resistance. The clad layer is of the order of 100 μm in thickness and it is difficult to determine the mechanical properties of this layer by conventional mechanical testing techniques. Nanoindentation is ideally suited to determining the elastic and plastic properties of such layers and here we report on a combined approach using experimental nanoindentation and finite element analysis to extract yield stress and strain hardening exponent for an Al-clad system. The approach used was calibrated against results for an Al 2024-T351 alloy, where conventional mechanical testing data was available. For the Al 2024-T351, a forward analysis was used for extraction of load–displacement curves at different indentation depths with the help of elastic–plastic properties obtained from tensile testing. For a ∼100 μm clad layer of pure aluminium on Al 2024-T351, reverse analysis was used for extraction of elastic–plastic properties from a single indentation test. A yield stress of 110–120 MPa and a value of 0.075–0.1 for the work hardening exponent was obtained for the Al cladding. Nanoindentation properties including maximum load of indentation, contact depth, area of contact and pile-up obtained from the forward and reverse analyses showed excellent agreement with the experimental results.