Aluminum Copper Alloy Experiment

[Joules]

The slag is dross and impurities that precipitate out of the metal to the melt/crucible wall.   I was thinking your aluminium bronze wouldn't be true, but as you created it in a steel crucible it will have pulled some iron out of the metal into the melt.   Casting molten metal into moulds is almost a chill process as the temperature drops off quite rapidly.  if you can slow the cooling to extended times you will form large or even single crystal components as in Rolls Royce turbine blades, though they have a little more trickery than just that.   Watching the big forge hammers "beat the crap out" of metal is probably the simplest way of explaining whats happening.   You are purifying the metal by squeezing out impurities that would remain in the metal and create weakness across the grain structure.  The heat allows the impurities to migrate through the metal, as when it cools they are locked in.

[NormanV]

Thank you Joules for taking the time to read my questions and to reply. What you say makes sense. Now I just have to translate that into action and make my metal machinable.

[Joules]

Norman, as mentioned by others.  It work hardens rapidy and is really abrasive on HSS tooling.  You know when you have it wrong as the metal screams at you, and watch if you drill it, the metal is really grabby and will clamp down on a drill bit and shatter it.   LOL those have been my experiences with Ally Bronze, does make great bearings though.

[NormanV]

I've just been into the workshop and tried to drill it. After my heat treatment it seems to be harder than ever!   
At the moment it feels very disappointing, I searched for a long time to find some scrap copper. It took a long time to melt it and the result is....... difficult!
This is the problem when you experiment to try to save money, it can turn out cheaper to buy the thing that seemed so expensive in the first place.
No worries, I have learned something new and I will remember it because I did it and did not just read it.

[mattinker]

The answer to your question about why your alloy is not sof when cooling down after casting might be in this article.

http://mit.imt.si/Revija/izvodi/mit144/slama.pdf

The scale forming on the outside of you steel crucible looks like oxidisation.

Have fun with your traction engine on the beach!

Cheers, Matthew

[Joules]

What he said above....   

High heat and long cool down times, in hours not minutes.

If i didn't have the furnace, it would be wrapped in stainless shim and put in the the stove with coals burning bright for 30mins+ then run the stove down slow and move the metal out of the hot zone.   Might as well do some jacket potatoes as the heat comes down.   

[NormanV]

I put it in the furnace, heated it up to a nice red heat and then blocked the orifices. I'll leave it till the morning to cool and then see how it is tomorrow.

[David Jupp]

I noticed that some of the stuff quoted mentioned a high temp solution heat treat and quench to soften, followed by a lower temp age hardening, whilst other stuff seemed to suggest a very slow cool from high temperature for softest condition.  Seems like some possible confusion here, or that things are very dependent on actual alloy composition.

If composition is not very close to a published spec, expect that you may have to experiment to find exactly what gives the behaviour you desire (perhaps limited by heat treatment facilities available).

[sparky961]

This is the problem when you experiment to try to save money, it can turn out cheaper to buy the thing that seemed so expensive in the first place.

It's taken half my life for this one to finally sink in!  I still have days where I temporarily forget.

No worries, I have learned something new and I will remember it because I did it and did not just read it.

But alas, this is why I don't regret the learning process.

[NormanV]

This metal melting mallarky is mystifying! My first attempt at making aluminium bronze took nearly 5 hours to melt 3kg of copper plus 300g of aluminium. This produced an alloy that was almost unmachinable. Even after annealing. I decided to dilute it 50%.
I placed 2kg of aluminium in the crucible and when that was melted I added 2.3kg of my bronze. The total time to when it was ready to pour was 1hr50min. I was ready for another 4-5 hour stint!
I am waiting for it to cool down to see whether I have an alloy that will do the job.
This is such fun!

[NormanV]

I've just tested a piece. A file cuts it and it compares quite well with steel in its resistance. It turns ok but not a great finish and it is drillable. I'm going to use it for the bearings for my traction engine which is not going to see a lot of use so it should be good enough.

[mattinker]

You melted the Al first in the second attempt. Molten Al is very corrosive and will dissolve copper at well below it's melting point I think you will find the melting point of your Al bronze should be just a little above that of the Aluminium.

Regards, Matthew

[seadog]

I don't think it's corrosive. What does happen is that a eutectic alloy forms which has a much lower melting point than the copper.

[mattinker]

I don't think it's corrosive. What does happen is that a eutectic alloy forms which has a much lower melting point than the copper.

I don't doubt you for a minut! I was told it was corrosive, but I think your explanation sounds better! I know that the resulting alloy has a lower melting point than copper. I can't find it now, but if I remember correctly, it's just a little over Al, which is very handy.

[seadog]

When I was doing Engineering Science, a new A level for 1968, our teacher demonstrated this by heating a piece of copper strip whilst rubbing an aluminium rod against it. When the temperature reached the melting point of aluminium he  was able to push the rod through the copper. I don't think it reached more than a dull red heat.

[SwarfnStuff]

These last few posts reinforce to me the reason I like this forum. "I learn stuff." 
   In this case it actually confirmed what I sort of knew but Eutectic was a word I failed to recall but sounded sort of familiar.
   Thanks
John B

[NormanV]

I've had a go at making a part. It turned like cast iron with dust instead of curly swarf. It drilled but blunted the drills and it was too brittle to do anything with it.
Not a success.

[PekkaNF]

Aluminium alloys can be funny. My brother told few years back about some rivets used in aeroplanes. Can't remember exactly how it went but there was a very exact heat treatmen cycle and if I remember right there was a little time, something like few hours rivets kept froxen, really cold, something like -60C just before use and riveted in very conrolled manner and then they age hardened in two hours or so to full hardness.

Pekka

[Meldonmech]

 
   I have found this to be a very interesting topic, with practical experience combined with technical facts.
 I tried to produce a copper/aluminium alloy some years ago using copper wire to the melt. The percentage copper was quite small, and the difference in machined surface finish was similar. The intention was to produce duralumin but I never got round to doing any strength or wear tests.
 On my next melt, the aluminium is from the same source and I will use copper wire. From what I can remember only a small percentage of copper is required, to substantially increase the strength. I also have some small brass pipe  fittings and use some of these in a melt to compare  the results.

                                                                                                      Cheers David

[NormanV]

My last post on this subject. (famous last words!)
I had cast an ingot 100x40x250mm from the 50:50 aluminium:copper mix. I took it in my workshop and dropped it half metre onto a concrete floor. It snapped in two!
I don't think that this alloy has any practical use.
I will save it to use to add small amounts of copper to future melts.
This alloying business is quite complicated!

[WeldingRod]

If you really want a hard alloy try Beryllium with Copper. It’s used to cover expensive golf clubs and can be used for armour piercing bullets!

Please don't play with Beryllium; it's toxic.  The machining award from it is too.  We use Beryllium Copper for downhill tools, and it requires special handling in the machine shop.

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[WeldingRod]

I have just cast another alloy, 90% copper 10% aluminium. I tried a file on it and it just skidded with barely a mark. It is certainly hard, will I be able to machine it? I'll find out tomorrow.
What I found interesting is the colour, with all that copper I expected it to be bronze coloured but it is silver with just a blush to it.
The copper that I used was old plumbing pipes with a few brass glands on it, so the actual composition if a bit vague.
One problem that I encountered was the low heat output of my propane torch. When I melt aluminium it normally takes approx. one hour to melt my 3kg ingots. I had thought that this was due to the size of the ingot, I have read of people having molten aluminium in 15-20 minutes.
Today I melted the aluminium first and then added the copper, from start to finish was over 4 hours! After two hours I almost gave up but by that time I had invested so much gas into the project I thought that I would see it through. I don't think that I will be trying to melt any iron with this torch.

My experience was that my random aluminum bronze was brass colored, quite hard, and super brittle.  I shattered some parts just getting them out of the sand.

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[RotarySMP]

The rivets referred to above are -DD rivets. The need to be heat solution heat treated, and come of of the heat treatment in the unstable "W" state, where they are soft, but will naturally age harden. You keep them in a chilly bin with liquid nitrogen to retard that process, long enough to insert and rivet a whole batch in a shift. They are very nice to rivet with, as they are nice and soft. They are normally only used by the manufacturers. For repairs, -AD rivets are used, which have a stable heat treat, and are a fair bit harder to drive.

With resect to aluminium bronze, this patent https://www.google.com/patents/US3378413 has an interesting line:
 With the conventional copper-aluminum-iron alloy, lower annealing temperatures in the' range of 800 to 1050 F. cannot be used because the martensitic structure transforms to eutectoid which results in a more brittle alloy having reduced strength and loss of ductility.

The present invention is based on the discovery that by adding nickel, or nickel and manganese, to an aluminum bronze alloy containing from 10 to 12% aluminum, the tendency of the martensitic structure to transform to the eutectoid is substantially suppressed. The suppression or elimination of the tendency to form the eutectoid enables the alloy to be stress relieved and permits secondary alpha precipitation at a temperature in the range of 800 to 1050 F. to thereby produce an alloy having high tensile strength and high yield strength with good ductility. The aluminum bronze alloy treated in accordance with the invention compares favorably with the more expensive cast and heat treated beryllium copper alloys.

So basically Cupper/Aluminium/Iron alloy, is probably pretty useless, as you confirmed.
Mark

[vtsteam]

Photos restored after Photobucket broke the links.

Interesting re-reading this thread. Just wanted to point out that I began it by trying to compound a specific silicon and copper bearing aluminum alloy, rather than an aluminum bronze -- which is a copper alloy with some aluminum in it . Quite a different purpose and metal alloy.

The aluminum alloy I chose to try to make was EN AC-45000. Which is 6% silicon and only 4% copper. I think that was a success and it certainly machined fine. I will have to check it again now for hardness after aging a further 3 years. I did make a part for the lathe project  with it -- a base extension.