Author Topic: Making Zamak ZA-12 from Zinc  (Read 688 times)

Offline vtsteam

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Making Zamak ZA-12 from Zinc
« on: December 04, 2020, 12:50:14 PM »
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:
I love it when a Plan B comes together!
Steve
www.sredmond.com

Offline vtsteam

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Re: Making Zamak ZA-12 from Zinc
« Reply #1 on: December 04, 2020, 02:35:26 PM »
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:
I love it when a Plan B comes together!
Steve
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Offline Bee

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Re: Making Zamak ZA-12 from Zinc
« Reply #2 on: December 05, 2020, 06:45:24 PM »
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.

Offline vtsteam

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Re: Making Zamak ZA-12 from Zinc
« Reply #3 on: December 05, 2020, 10:36:32 PM »
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
I love it when a Plan B comes together!
Steve
www.sredmond.com

Offline Kjelle

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Re: Making Zamak ZA-12 from Zinc
« Reply #4 on: December 12, 2020, 05:06:27 AM »
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

Offline vtsteam

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Re: Making Zamak ZA-12 from Zinc
« Reply #5 on: December 12, 2020, 11:01:10 PM »
Hi Kjelle, thanks! what are you up to these days?  :beer:

Yes, the more I think about it the more it makes sense that dissolving a metal in another metal could be inhibited by too fast a heat. Zinc has to be poured when it is not too hot, or it flares up. Aluminum and copper take time to dissolve in it, so it seems logical that you should keep zinc just above its melting temperature, and not hotter, while waiting for the others to be absorbed. That will take time. Too fast a heat will force you to pour before the others have a chance to begin to dissolve.

I'm re-lining my oil fired furnace to do some iron casting, next.

I love it when a Plan B comes together!
Steve
www.sredmond.com

Offline mattinker

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Re: Making Zamak ZA-12 from Zinc
« Reply #6 on: December 13, 2020, 07:45:02 AM »
Hi Steve,

My personal experience has been, melt the Al, just above 640C dissolve in the Cu (I use very fine electrical wire) stop the heat source, and feed in the Zn. As the Zn content rises, the melting point will drop. If it "flares up" you are way to hot, remember the boiling point of Zn is 700C so, if you start adding the Zn at just above the melting point of the Al, it won't get above 700C. Pyrometers with a K type thermocouples are very cheap now, the IR pyrometers don't always work on molten metal!         Cheers, Matthew

Offline vtsteam

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Re: Making Zamak ZA-12 from Zinc
« Reply #7 on: December 13, 2020, 04:49:56 PM »
Interesting Matthew. Sounds like an excellent and precise way to go about it.  :beer:

I'm doing my whole melt at about 450C, and using ordinary soft copper tubing. No problem with zinc flare, and I seem to get good results, too.

Zinc is pretty forgiving stuff, until you get up to dealing with it when brass melting. Then it can be tricky. I think a pyrometer would be useful there for me. Think I'd want a type R, however, because of the iron furnace. But so far, have managed pretty well without any of them.
I love it when a Plan B comes together!
Steve
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Offline vtsteam

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Re: Making Zamak ZA-12 from Zinc
« Reply #8 on: December 14, 2020, 09:08:35 AM »
Speaking of pyrometers. Matthew, the type R are very expensive, using rare metals. As you say, the new digital IR pyrometers may not work well with molten metal.

There is one other type, not expensive, which I've been meaning to build. That's an incandescent filament comparative pyrometer. About 5 years ago I found this DIY version here. Glad the site hasn't disappeared yet:

https://www.metallab.net/pyrometer.php
I love it when a Plan B comes together!
Steve
www.sredmond.com

Offline mattinker

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Re: Making Zamak ZA-12 from Zinc
« Reply #9 on: December 14, 2020, 09:27:33 AM »
Steve,

I have both a Ktype and an IR pyrometer, the Ktype is rated up to 1260C, so, it should be useful for cast iron as well!

Cheers, Matthew

Offline Lew_Merrick_PE

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Re: Making Zamak ZA-12 from Zinc
« Reply #10 on: December 14, 2020, 04:22:55 PM »
According to ILZRO

 The chemical composition of zinc-aluminum ZA12 alloy is given in the following table.
Element    Content (%)
Zinc,Zn    Remainder
Aluminum,Al    11.5
Copper, Cu    1.2
Iron, Fe    0.075
Magnesium, Mn    0.03
Lead, Pb    0.006
Cadmium, Cd    0.006
Tin, Sn    0.003

Does this help?  --  Lew

Offline vtsteam

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Re: Making Zamak ZA-12 from Zinc
« Reply #11 on: December 14, 2020, 05:45:03 PM »
Actually, Lew, the iron, lead, cadmium and tin you mention are maximums, ie contaminants. Primary constituents of ZA-12 are the zinc, aluminum, and copper, and a trace of magnesium.

Also per ASTM the aluminum in ZA-12 can range 10.8 - 11.5% and copper 0.5 - 1.2%.

I used 11% and 1% respectively. The aluminum I used probably had some magnesium in it. But all of this is relatively academic when using scrap sources, as I do, eg. copper tubing and my "soft" aluminum round cutoffs from a machine shop.

Nevertheless it cast well, machined well, and I have a 5 year old lathe with similar homemade Zamak "ZA-12" in headstock, carriage, tailstock slide, etc.
I love it when a Plan B comes together!
Steve
www.sredmond.com

Offline vtsteam

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Re: Making Zamak ZA-12 from Zinc
« Reply #12 on: December 14, 2020, 11:23:42 PM »
Matt, can't say for sure because I haven't used one, but I think 1260C limit for the pyrometer seems low for iron foundry work. But willing to be corrected!  :wack:

Terry Aspin used the stir stick test -- if a 3/8" steel poker used for stirring the melt comes out with a clump of iron on it, it's too cool. If it comes out shiny and maybe even pointed (from melting) you're good to go!
I love it when a Plan B comes together!
Steve
www.sredmond.com

Offline mattinker

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Re: Making Zamak ZA-12 from Zinc
« Reply #13 on: December 15, 2020, 05:44:33 AM »
Steve, it is low for Iron but useful! Good for Bronze brass zinc and Al!

Cheers, Matthew