X-ray diffraction line profile analysis for the detection of the propensity to sensitize

Abstract

Prior studies have revealed that the sensitization kinetics of 5xxx-series Al-Mg alloys are responsive to the dislocation content, with lower dislocation densities leading to higher rates of sensitization. In this work, X-ray line profile analysis (LPA) was employed to non-destructively assess the dislocation density in 5083 and 5456 alloys samples in various tempers and thermomechanical processing states. Using a conventional laboratory powder diffractometer with a Cu-Kα sealed tube source, it is shown that the approach has the ability to discriminate between samples of disparate tempers (H131, H116, and solutionized and water quenched). Destructive electron backscattered diffraction (EBSD) measurements on select samples confirm the variations, from the perspective of geometrically necessary dislocation density. Experiments were also performed using softer X-rays generated using a Cr Kα sealed tube source, which would render the approach more portable, due to lower shielding requirements. Unfortunately, Cr radiation was not successful due to the limited number of accessible diffraction peaks. Using the dislocations densities measured using LPA together with an established constitutive model permits accurate prediction of the mechanical strength of the alloys of the above disparate tempers. However, the technique does not appear capable of discriminating between samples within a given temper (e.g., H116). Use of a more highly monochromatic X-ray source could render the technique useful for a comprehensive structural health monitoring system for 5xxx alloys prone to sensitization.