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Making Zamak ZA-12 from Zinc

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vtsteam:
I needed to make some ZA-12 from pure zinc today, and don't recall if I ever mentioned how I've done that by melting the constituents together.

If not, here goes. I use a proportion of 88% zinc, 11% aluminum, and 1% copper. In my case the zinc was in ingots from a commercial foundry, the aluminum was soft aluminum round bar stock ends from a machining outfit making parts to be anodized, and the copper was some 3/8" soft copper tubing.

I put all ingredients together into a crucible today, and didn't try to melt the aluminum first -- which might have seemed more logical considering its higher melting point than zinc. And the copper has even a higher M.P. But, no, from past experience I guessed that the zinc would dissolve the aluminum, and the aluminum would in turn dissolve the copper, once it was in solution.

And this turned out to be exactly right. The zinc melted first, then attacked the aluminum, and finally the mix dissolved the copper. This was all done without having to go to an elevated temperature which would have fumed the zinc. The heat up was reasonably gradual in my Plaster of Paris lined propane foundry furnace, and I actually turned off the burner for a short period for a heat soak while the aluminum was dissolving and I pushed it under the surface a few times with a poker. It floats on zinc.

A faster and hotter furnace, might have been problematic, and it may have overheated the zinc before the aluminum even appeared to be dissolving. This brings up an interesting point. If I recall correctly I also once did a named aluminum copper alloy recipe as an experiment here, and successfully melted the copper into the aluminum, while Ironman reported that he'd had trouble melting copper into aluminum.

Since this earlier experiment and my zamak melt are both eutectic (dissolving) processes rather than true melting, maybe the reason for the problem was that his furnace was much faster to reach temperature -- Ironman, if you still read here, could that have been it?

With  the furnace's admirable Kaowool insulation, reflective hot coating, and powerful burner, it's possible that the copper never had time to dissolve before the aluminum just had to be poured. As we all know from making lemonade and watching the sugar swirl around at the bottom of a pitcher, dissolving things can take some transitional time. Compared to melting from solid to liquid, which happens within a few degrees.

Anyway, that's how I made Zamak 12, today. :beer:

vtsteam:
After casting a ball handle today, I have to say that the cast material has sawn and filed far easier than the Zamak I've used in the past. Files did not skid and a hand hacksaw went through it just a little slower than aluminum. It seemed less skiddy and soft. More crisp.

Hmmmm, what gives? My past experience machining Zamak 12, boring my lathe's headstock was a real pain! Was it really Zamak 12 that I was using? I've used foundry supplied Zamak 2 in the past, was that what I'd used?

I had to re-read my lathe build thread and finally found a post just before the pour which said I had used "homemade Zamak 12", but the mix was different then: 89% zinc and 11% 6061 aluminum.

It made sense, since 6061 aluminum should supply the missing copper in about the right percentage. But I now find there are definitely better working properties with this newer mix, where I used soft aluminum and supplied the copper separately. Don't know why, but I'm going to remember this for future use. Just thought you might want to know.  :beer:

Bee:
Interesting approach. Like a friend on mine recently making (lead tin) solder instead of just finding some old stuff now that lead is banned. Why are you using zamac when you have the capability to use aluminium? I always thought zinc based things were just for the accountant's benefit.

vtsteam:
Not even sure where to begin. Well, anyway, welcome, have a look around. Read some threads.  :beer:

https://madmodder.net/index.php/topic,8191.0.html  aluminum casting
https://madmodder.net/index.php/topic,8739.0.html  cast iron
https://madmodder.net/index.php/topic,10542.0.html zamak casting

And in particular read this page:

https://madmodder.net/index.php/topic,10542.650.html

Kjelle:
Hi Steve!
Nice to see you back at it again!
Now, I don't know squwat about casting, but had some theoretical education on it 40-some years ago, and your assumption seem right. Somewhere, sometime, I saw something about melting times and when making alloys, you had to take "heat soak time" into consideration... But I don't remember where and when, it might just be "common sense" (Yea, that thing missing everywhere today!)...

Interesting it was, to say the least!

HAve a nice week end!

Kjelle

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