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I'm just getting-into melting-down cans to make aluminum-based slingshots, hammers and the like. In my ignorance I didn't realize that copper/brass were also things that I could process which has left me hoping to learn:

  • should I be looking to make an alloy or using 1 metal and, if 1, which would be optimal?

  • are there any "additional treatments", such as quickly cooling the hot metal-product into a block of ice, or perhaps having the casting box on a vibrating-panel to further 'settle' things? All I know to do for increased-strength is to make as-clean-as-possible a mix IE scoop as much slag/skim from the top of the molten metal as possible!

  • is there enough variance among aluminum (or non-alloy metal products) to make it worthwhile to source specific-types, IE maybe aluminum from a car-engine part will make a stronger/better ingot than one made from a heap of aluminum cans?

A hammer and a sling-shot are my 1st goals with this, so while I'm not the best at knowing 'strength-types' I don't think "tensile" strength will be as important as yield-strength or compressive-strength but not sure, if I've gotta choose between optimizing for the slingshot OR the hammer, the hammer is far more important (and I'm not interested in working with lead to do this!)

Thanks a ton for any insight on this am in the middle of diving-in, learning I could do this at-home was truly a christmas-present LOL :)

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  • $\begingroup$ Have you checked the local library for books on casting etc? $\endgroup$
    – Solar Mike
    Dec 14 '19 at 19:59
  • $\begingroup$ The big problem is that any scrap metal is already an alloy of unknown composition, unless you can trace exactly where it came from. Aluminium used in the food industry will also have coatings applied. For example "brass" may be anything from 50% to 90% copper and the rest mostly zinc (but there may some lead as well). An aluminium engine block may contain up to 5% magnesium as well as aluminium. Unless you plan to go very deep into this, or buy your raw materials as known alloys, it is likely to be a more about "try it and see what works" than "scientific metallurgy". $\endgroup$
    – alephzero
    Dec 14 '19 at 20:49
  • $\begingroup$ Solar Mike - No I haven't, I used to be a library-rat but in past half-decade have found the web FAR more efficient for virtually everything (what I learned in 1hr online Re alloys, would've taken many hours longer at the library) @alephzero - What if I just used known-alloys, for instance if I wanted to make a slingshot from 7075 aluminum, could I simply feed a chunk of 7075 alum into my crucible then cast with it? Also, w/ a laser thermom for surety, is it feasible to temper at-home, like 7075-T6 or -T5? Seems I'd just need an appropriately-sized forge/kiln & a laser thermom+timer! $\endgroup$
    – user23895
    Dec 28 '19 at 15:48
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Copper with aluminum is called aluminum bronze in the trade; no zinc. Up to about 10% aluminum and a couple % iron . That system will get to about 300 BHN / Rc 30; a respectable hammer - not ductile. Manganese bronze is copper with 30 % zinc and a few % Al , Mn, and iron , also a very strong system for copper alloys . Copper Development Association will have more info. On the otherhand , I can't imagine how you could make them in the "backyard". I used to work at a smelter that produced these and other alloys and even with full foundry and lab facilities the melter would keep his fingers crossed on the aluminum and manganese bronzes because it was not a simple matter of getting chemistry in the right ranges but also getting ratios correct such as Al/Fe, Al/Mn , and others. I suggest staying with copper + 9 % aluminum , no zinc, and see what happens. If you get in the ballpark , aluminum bronze has a narrow freezing range and requires a large riser to get a sound casting. I hate to say it but both aluminum and manganese bronzes have a "martensite" reaction and can be heat-treated but not nearly as much affect as steel heat treatment. For now just stay with melting.

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  • $\begingroup$ THANKS!! I've just been doing beer-cans, have made a few pounds'-worth of ugly castings as I get better at shaping styrofoam for my forms, at any rate a couple things occurred to me that I'd love to know if-possible: - Tempering seems like something I could do if I made a special forge/furnace for it & used a laser-thermom, am I on-point thinking this? $\endgroup$
    – user23895
    Dec 28 '19 at 15:50
  • $\begingroup$ Hit Enter before asking the more-important Q!! Instead of messing with mixing metals to make my own alloys, am I correct in thinking "the crucible gives-back what's put in"? IE, could I just take a known quantity of 7075 aluminum, molt it and cast with it, and know I have 7075 castings? Thanks!! $\endgroup$
    – user23895
    Dec 28 '19 at 15:52

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