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Q&As since 1989
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Looking for aluminum casting information
Q. Dear Sir,
My name is Gerry Lynas. I am a sculptor and designer living in NYC. I am interested in aluminum sculpture and aluminum casting methods and materials other than traditional lost wax. I see that you represent a number of sculptors who work in aluminum and am particularly interested in small scale graphite and sand casting techniques and materials. I am working with a resort in the Caribbean that has initiated a recycling program that will produce fine art from aluminum cans. Any information that you can provide would be most helpful. Thanks very much.
Sculptor - New York, New York
2007
A. Smelting of aluminum cans is best left to major operations. Due to a high surface area-to-metal ratio, there is a high impurity content: pretreatment coatings (phosphate or chrome-phosphate), ink or paint, clearcoating such as vinyl, acrylic or lacquer, and dirt. Nasty smoke and lots of possibly toxic slag when melted (and dangerous if any water is present), and the thin metal easily oxidizes unless covered with flux. The aluminum companies clean and de-lacquer before smelting, and then use a higher-than-usual amount of chlorine gas to refine the melt.
The can body is usually alloy 3004 and the lid 5182. Overall composition is about 95.65 wt% Al, 0.2 Cu (max), 0.6 Fe (max), 1.9 Mg, 0.9 Mn, 0.3 Si (max), 0.25 Zn (max), 0.2 others (max). Doesn't correspond to any casting alloy. From a brief Internet search, hobbyists smelting aluminum cans obtained 40 to 75 wt% metal, and only one claimed to have produced good, shiny castings. Adding 2.7 and 4% Zn would give approximately alloys 705.0 and 707.0, respectively (although Mn is a bit high, and Cr & Ti a bit low). These are sand casting & permanent mold alloys. Properties are poor with respect to casting fluidity, hot tearing and solidification shrinkage; good w.r.t. machining, polishing, anodizing & corrosion resistance.
Melting ranges: alloy 705.0: 1105-1180 F (596-638 C), alloy 707.0:
1085-1165 F (585-629 C).
If you proceed, let us know how things turn out.
- Goleta, California
Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015.Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at finishing.com, continue to benefit from.
2007
Casting of 6061-T6
Q. I am working in a foundry that like to develop castings with material 6061-T6. Unfortunately the shape of the casting are quite intricate so could not use T6 blocks or billets. So we are thinking to melt 6061 and cast into shape and heat treat to get T6. From this we plan to machine.
Would like to inquire if this is possible and what is the proper heat treatment procedure to avoid cracking.
Foundry Metallurgist - San Pedro, Laguna, Philippines
September 30, 2015
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