1 7 ADVANCED MATERIALS & PROCESSES | NOVEMBER/DECEMBER 2023 micrographs from an AA7075 (upper sheet) joined to AA6111 (lower sheet) by resistance spot weld. The low magnification image montage shows the grain structure in both alloys; however, there is higher grain contrast in the AA7075. The etch is also effective at revealing the microstructure in the partially melted zone (PMZ) of the resistance spot weld as shown in Fig. 2b. There are other applications including friction stir welding and explosion bonding where the Papageorge two-step etching process may provide high quality images of dissimilar joints that were not possible using currently available etches. Work is underway currently to investigate other types of joints using this etching procedure. BEST PRACTICES There are a few practical notes to discuss when working with the Papageorge two-step etchant. The samples must be freshly polished for the etchant to work properly. Based on the experiences during this work, the samples must be etched within fifteen minutes after the final polish is completed. When the samples are left to sit out for several hours before etching, the second step of staining does not produce a uniform and even contrast. The etchants used in this work were always mixed immediately before use (e.g., not stored and reused). This is simply due to a policy in this shared teaching lab that no etchants are stored long term to avoid the problem of chemicals being left in the lab for long periods and often abandoned. It may be possible to store these etches and reuse them more than once, but that was not the procedure followed in this work. The last practical point that was observed during this work was that this etching process works better when the sample is swabbed only once with the modified Keller’s reagent in step 1 and immersed only once in the modified Weck’s reagent in step two also. It was possible to do a second immersion in the modified Weck’s; however, in this work that often led to nonuniform staining of the etched surface. It is recommended to do some development work and optimize the process for the specific alloys and samples of interest to create specific times for each step of the Papageorge two-step etch for use in teaching, training, or production support work in each laboratory. CONCLUSIONS The results of a new etching procedure, the Papageorge two-step etch, were presented. The etching procedure was proven effective for creating grain contrast in 2000, 5000, 6000, and 7000 series alloys. The Papageorge two-step etch also worked effectively to create grain contrast on a resistance spot weld cross-section from a sample fabricated from a 6000 and 7000 alloy. The etching procedure has proven straightforward for novice metallographers and offers an option to use a single etchant to simplify sample preparation in the laboratory. ~AM&P For more information: Elvin Beach, Associate Professor of Practice, Materials Science and Engineering Department, The Ohio State University, 140 West 19th Ave., Columbus, OH 43210, beach.110@ osu.edu. References 1. B. Jowett, Plato’s Republic: The Greek Text, 3(82), 1984. 2. M. Warmuzek, Metallographic Techniques for Aluminum and Its Alloys, ASM Handbook, Volume 9, Metallography and Microstructures, ASM International, p 711-751, 2004, doi. org/10.31399/asm.hb.v09.a0003769. 3. M. Mohammadtaheri, A New Metallographic Technique for Revealing Grain Boundaries in Aluminum Alloys, Metallography, Microstructure, and Analysis, 1, p 224-226, 2012. 4. A. Tamadon, et al., Development of Metallographic Etchants for the Microstructure Evolution of A6082-T6 BFSW Welds, Metals, 7, p 423-440, 2017. 5. E. Beach, et al., An Etching Technique for Characterizing Friction Stir Welds in Aluminum Alloy Tailor Welded Blanks, Metallography, Microstructure, and Analysis, 7, p 630634, 2018. 6. W. Papageorge, et al., Development of a Versatile Two-Step Etchant to Reveal Grain Boundaries in Multiple Aluminum Alloys, Metallography, Microstructure, and Analysis, 2023, doi. org/10.1007/s13632-023-01008-3. 7. ASTM E3-11(2017), Standard Guide for Preparation of Metallographic Specimens, ASTM International, West Conshohocken, PA, 2003, doi. org/10.1520/E0003-11R17. Fig. 2 — Optical micrographs of a resistance spot welded sample. The image in (a) is a low magnification image montage of the RSW showing the AA7075 (top sheet) and the AA6111 (bottom sheet) after etching with the Papageorge two-step etchant. The micrograph in (b) shows the partially melted zone (PMZ) in the AA7075, and the micrograph slice in (c) shows the grain structure in the parent metals, PMZ and weld of the dissimilar alloys. (a) (b) (c)
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