Metallographic Etching of Al–Mg–Zn–(Cu) Crossover Alloys

Abstract

Various alloys demand customized etchants due to their diverse chemical compositions, particularly in the realm of aluminum alloys. Consequently, this study proposes a technique for metallographic visualization of small grain structures within Al‐Mg‐Zn‐(Cu) crossover alloys. The method relies on a thermal pre‐treatment combined with an etching process. The study primarily seeks to comprehend how grain boundary precipitation affects etchability, addressing the complexities of characterizing these alloys. The demonstrated approach facilitates the swift assessment of grain sizes <10 µm using light optical microscopy. Exploring the etchability of Al‐Mg‐Zn‐(Cu) crossover alloys across a standard heat treatment pathway identifies the optimal treatment and suitable etchant for grain visualization. Through process refinement, a reduction in processing time is achieved by employing a single‐step preheat treatment lasting 20 minutes at 180 °C post solution annealing. Transmission electron microscope analysis reveals continuous occupancy of the grain boundary with T‐phase as the key factor influencing the alloy’s etchability. Grain size assessment involves line intercept counting and euivalent circle diameter (ECD) measurement for precise characterization.This article is protected by copyright. All rights reserved.