A new light optical metallographic technique for revealing grain structures of common 2000, 5000, and 7000 series aluminum alloys
- Kaiser Aluminum and Chemical Corp., Pleasanton, CA (United States). Center for Technology
A new metallographic technique has been developed for revealing the grain structures of common 2000, 5000, and 7000 series aluminum alloys. This technique consists of four steps: (1) The aluminium alloy is solution heat treated and water quenched so as to keep soluble elements such as Cu, Mg, and Zn in supersaturated solid solution. (2) An optimized precipitation heat treatment then produces relatively coarse precipitates at grain boundaries and fine precipitates in the grain interior. These precipitates are {theta}-CuAl{sub 2} + S-Al{sub 2}CuMg in 2000 series, {beta}-Mg{sub 2}Al{sub 3} in 5000 series, and {eta}-MgZn{sub 2} in 7000 series aluminum alloys. (3) Metallographic samples are prepared from materials heat treated as specified in steps 1 and 2. The samples are then polished and deliberately overetched. The relatively coarse grain boundary precipitates accentuate the chemical attack at the grain boundaries. (4) The overetched sample is then lightly polished to remove etch pitting and etched precipitates in the grain interior. Excellent grain boundary contrast is now produced. The grain contrast of samples prepared with this technique is far superior to that of any existing etching technique for aluminum alloys. This new technique will make grain-size measurement much easier and more accurate. In this paper, the metallurgical and metallographic principles related to this novel etching technique are presented.
- OSTI ID:
- 532953
- Journal Information:
- Materials Characterization, Journal Name: Materials Characterization Journal Issue: 3 Vol. 38; ISSN 1044-5803; ISSN MACHEX
- Country of Publication:
- United States
- Language:
- English
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