In situ observation of precipitation processes in aluminum alloys via high-resolution STEM

Light alloys based on aluminum are an exceptionally versatile class of materials. They combine low weight and corrosion resistance with adjustable material properties, tunable by alloying with other materials or by subjecting them to accurately defined temperature treatments.A popular approach is the strengthening of alloys formed from aluminum and copper by age- or precipitation hardening: Performing a careful series of temperature steps triggers the deliberate formation of a certain type of precipitate, yielding a material with defined hardness.During this artificial ageing process, the supersaturated crystal starts to form small precipitates with a diameter of only several nanometers. When the procedure continues, they start to grow, forming different and larger types of precipitates, with massive impact on material properties.(1)Commonly, investigations of precipitation processes rely on macroscopic mechanical testing and microscopic investigations of samples taken at various stages of the procedure. In situ TEM methods can be a valuable contribution for this field, since they provide immediate insight in the relevant processes on an atomic level while they are happening.(2)In this study, we use in situ STEM for the investigation of nano- and microscale effects of temperature treatment on AlCu4. We directly capture growth and decay of the precipitates during various stages of the heating experiment, as illustrated in Figure1. Concomitant analytical investigation with EDS and EELS allows for in-depth “live” visualization of phase separation dynamics.This high-resolution approach provides novel insights into precipitation processes in aluminum alloys, adding a new perspective for material development and optimization.