Heated-Stage Small-Angle X-Ray Scattering for Quantification of Precipitate Fields and Their Evolution During Process Simulation of AA7050

Abstract

Optimization of properties in certain metallic materials relies on the ability to leverage precipitation strengthening effects via application of appropriate processing techniques, including heat treatment, to control precipitate morphologies. Traditional methods to monitor precipitate growth during heat treatment employ post-quench microscopy and hardness measurement, but these have limited ability to monitor small-scale or incremental changes in precipitate morphology that are relevant to material property profiles. Laboratory-scale small-angle X-ray scattering (SAXS) techniques in combination with heated-stage capability represent a novel approach for improved understanding of microstructural evolution and design of heat treatment schedules, by enabling analysis with high spatial resolution and time-dependent information. In the current study, heated-stage SAXS experiments were used to recreate four heat treatments on AA7050-T7451 alloys and successfully monitor precipitate growth over a temperature range of 160–220 ℃, with hold times of 0–120 min. SAXS measurements indicated precipitate diameters ranging from 7.1 to 9.8 nm, with increased precipitate growth corresponding to higher temperatures and longer hold times. Precipitate volume fraction and calculated hardness values ranged from 1.3 to 2.9% and 78–94 HRB. Results from this work indicate that laboratory-based SAXS is a highly accurate method for measurements at the nanometer length scale, as well as high temporal resolution, and this approach lends itself to both room temperature and high-temperature precipitate quantification, potentially eliminating the need for time- and resource-intensive synchrotron-based SAXS for precipitate analysis. Additionally, laboratory-based SAXS can facilitate a more accessible and economical investigation that is particularly beneficial for process design and analysis where higher-volume testing is required.

Graphical Abstract