In Situ TEM Observations on an Aluminium Alloy Elaborated by Laser Beam Melting

On metallic aeronautical materials, complete observations and characterizations of fine microstructures have been conducted to understand the origin of mechanical properties as well as temperature induced phases transformations. More specifically on aluminium alloys, known to be very sensitive to thermal history and elaboration processes, in situ TEM can be of help to understand the several mechanisms involved.<br/>On Laser Beam Melted Al-Si-Mg alloys, the rapid solidification induces a dendritic structure composed by α-Al cells and eutectic Al-Si frontiers. In this complex microstructure, in situ characterization was conducted to observe and understand:<br/>- The eutectic Al-Si walls effect on the hardening mechanisms,<br/>- The dislocation interaction with the nanometric inner cell precipitates.<br/>Thorough TEM characterization with several TEM preparation techniques have been conducted prior to the in situ straining experiment to determine the adapted preparation technique for such elaboration processes. This study revealed the need of PIPS preparation for the eutectic walls hardening effect observation and electro-polishing techniques for the nanometric precipitate’s role on the hardening mechanisms.<br/>Thus, with the right preparation technique association, in situ TEM experiments confirmed a preponderant role of the eutectic cell interfaces during room temperature strain to play a main role in Al-Si-Mg alloy mechanical properties.