Development of a Versatile Two-Step Etchant to Reveal Grain Boundaries in Multiple Aluminum Alloys

This paper describes an etching procedure to reveal grain boundaries in metallographically prepared samples from 2000, 5000, 6000, and 7000 series alloys. The etching procedure, named the Papageorge two-step etch, makes use of two established aluminum etchants with slightly modified chemistries. The first step in the etching process uses a modified Keller’s reagent to attack and activate the polished surface. The second step uses a modified version of Weck’s reagent to stain and develop contrast at the grain boundaries. The etching procedure is straightforward which aids in training novice users. Examples of successfully etched AA2024, AA5754, AA6061, AA7075, AA7475 and a resistance spot-welded sample of AA7075 and AA6111 are presented here. The Papageorge two-step etch offers metallographers the option to use one etch for revealing grain structures for a broad range of single alloys or joined structures fabricated with dissimilar aluminum alloys.