PDA

View Full Version : Alloying aluminum and zinc



SirLesPatterson
05-27-2014, 08:07 AM
I was just reading about a machining project in which the person used ZA27, a zinc-aluminum alloy, to make a dividing head casting. ( link (http://www.modelenginemaker.com/index.php?topic=826.0) )

I tinker with aluminum casting, and thought about casting in zinc but I hear that zinc can be a nasty thing to machine because of tiny razor/needle like chips that embed in everything from flesh to clothing. Yes, I know zinc is dangerous to melt too. Having on hand both cast aluminum scrap and zinc I would like to know people's thought about home blending a zinc-aluminum alloy? It appears a lower melting point and increased strength over aluminum only would be a benefit. What about blendability and machinability? Thank you.

ironmonger
05-27-2014, 09:58 AM
Zinc isn't inherently dangerous, it's the zinc oxide that results from overheating, read boiling, the zinc and causing it to 'burn' in the air that's a problem. Zinc's melting point: 419.53C or 787.15F and the boiling point: 907C or 1665F should make the alloy quite safe. If you can get pure zinc, possibly melting the zinc and adding the aluminum would be faster.

When I alloy bronze from pure metals I melt the tin first and add the copper. It melts faster that way. Mostly due to the surface area of the molten tin transferring heat faster to the copper by virtue of having it's 'feet wet' in a pool of molten tin. The zinc will melt and not boil and still be hot enough to melt the aluminum.

You would likely need some kind of flux. I would be mindful of maintaining a reducing atmosphere in your crucible furnace as well.

paul

Duffy
05-27-2014, 10:53 AM
I think that you are talking about "Zamak" alloys. One of them is Al 4%, Zn 95% and I think Cu 1%. I have melted zinc in a coke-fired furnace with few problems. I say "few" because one of them was when a bit of skimming dross spilled into the fire and a grand, but brief, plume of zinc oxide fume appeared. Otherwise, it melts easily in an iron plumber's solder pot. I have had no problem with overheating.
I vacation on an island off the New Brunswick coast, (Grand Manan,) and the lobster boats are serviced there by haul-out on the shingle at low tide, (20+ foot tide swings.) Zinc anodes, (virtually pure zinc cast onto a steel bolting strip,) litter the beach, and I collected all I will EVER need.
I have been melting scrap cast Al, (NEVER savage barbecues!) and cleaning and casting it in old cast iron muffin pans. I have done the same thing with the zinc. Have not gone to the next step because I need an assistant. My furnace is sized to #16 and #20 crucibles, (they were free,) and it is definitely NOT a one-man operation.
It is my intention to eventually cast both Zamack and aluminum, and then graduate to brass and then gun metal as I also have a supply of pure tin.

SirLesPatterson
05-27-2014, 11:11 AM
Thanks for the responses. I guess my biggest curiosity about a Zinc-Aluminum alloy is the machinability. Any experiences?

lakeside53
05-27-2014, 09:54 PM
It machines very easily. Small crumbly chips.

boslab
05-28-2014, 03:54 AM
Watch out for zinc, it sublimes, solid can go to vapour in one go, you always know when you have been exposed if you smoke, tobacco tastes real funky, burning and welding galv steel same effect, can make you ill, i tried it, metal fume fever, shiver ****e and shake, the best they could give us was milk to drink, not even sure if it helps
Machines as said crumbly, hard to get a finish on it without polishing with abrasive
Mark

ironmonger
05-28-2014, 10:00 AM
Watch out for zinc, it sublimes, solid can go to vapour in one go, you always know when you have been exposed if you smoke, tobacco tastes real funky, burning and welding galv steel same effect, can make you ill, i tried it, metal fume fever, shiver ****e and shake, the best they could give us was milk to drink, not even sure if it helps
Machines as said crumbly, hard to get a finish on it without polishing with abrasive
Mark

While I am cautious about zinc, and never pour brass at public demo's, it has nothing to do with zinc 'sublimating'. Zinc's boiling point is over twice the melting point. It will not sublimate. I don't use brass and the attendant zinc content as I am easily distracted... If you start talking to someone at a public demo and don't pay attention to the 'melt', bad things can happen.

If you do boil the zinc, the metallic zinc vapors will combine rapidly with any free oxygen and release even more heat, the formation of zinc oxide is an exothermic reaction. The resulting cloud of zinc oxide is definitely bad for your health. The blacksmithing community lost a member a number of years ago to 'zinc' poisoning. He attempted to burn of the galvanizing from some hardware in a confined space.

see:
http://www.anvilfire.com/iForge/tutor.php?lesson=safety3/demo

be safe
paul

boslab
05-28-2014, 08:56 PM
Ok to be precise, the oxide sublimates, ie the metal oxidises then the oxide vapourises, however which way you do it zinc can get into your body by heating the stuff, its called metal fume fever, it isnt imaginary and it certainly isnt safe, welding cutting or melting zinc can lead to this, as can overheating alloys containing zinc, i just want folk to be safe.
Mark

SirLesPatterson
05-29-2014, 07:10 AM
... Yes, I know zinc is dangerous to melt too. ...

This is why I stated this in my original query, I was trying to avoid being schooled on metal fume fever as I am well aware of the hazards and take great precautions. I do however suppose that it is quite important for others that might read this thread now and in the future to be made aware of the hazards. With that being said, boslab, ironmonger, thank you for contributing hazard information to this thread as it is VERY important.

On the original topic, I think I will attempt some alloying this summer. If I do I'll post an update.

Thanks!

Chaz
05-29-2014, 08:40 AM
Why bother trying to create the exact alloy when we are surrounded by scrap zinc alloy items? In my zinc alloy bucket there are bits of pressure washer, toy cars, windows catches, etc Doesn't seem to matter much what the zinc alloy came from, it all seems to cast well, machines nicely and makes good bearing material.

Chaz

michigan doug
05-29-2014, 03:10 PM
Proper precautions are not overly complex. Don't overheat the zinc and don't breath the fumes. Inhaling zinc fumes can kill you.

If this is for critical applications, you should buy proper alloy zinc. Castings using zinc of questionable purity can lead to zinc corrosion, aka zink pest.

http://en.wikipedia.org/wiki/Zinc_pest


doug

boslab
05-30-2014, 03:22 AM
A lot of the time making alloys like titanium steel, titanium ali adding boron as a grain refiner etc, the higher melting point component never melts at all, its actually dissolved not melted, like low carbon titanium steel, the mp of the steel is around 1450 or so and Ti wont budge till 1600 ish, you cant heat the steel to 1600 but adding Ti is just dump it in and wait for it to dissolve, some things dissolve fast like copper in steel, bang its right through the cast
Mark