Home made cast Aluminium

Biggest 'don't' is don't spill the hot metal - it spits like hell on earth or cement - work on a sandbed is best.

Biggest thing is safety.

I would not be casting metal inside my home - do it outside. Not only a danger of fire, but fumes and escape limitations.

Wear appropriate safety clothing - (thick) leather apron, heavy duty foundry boots (no openings at the toe end).

Keep water away from the area where metal is molten - it can cause an explosion if the two come together, as water takes up a huge volume when vapourised suddenly to those temperatures. Especially so, if molten metal is dropped into water. I believe (several?) were killed in a Welsh foundry accident when molten metal spilled onto a wet area, some years ago while the crucible was being transported from the furnace to the pouring area.

A lad at work was hospitalised while melting white metal (only 400 degrees?) from a large bearing when the liquid metal hit water.

We used to pour molten metal from a large crucible into water to granulate it - perhaps as much as 50kg at a time. The melted metal was often around 1800 degrees Celsius. A dangerous operation at the time as the crucible tipping device was operated by hand - with no brake - and not controlled remotely! The metal was poured (slowly) into rapidly swirling water from about a metre and a half and the tank was about 1000-1500l, as I recall.

Induction furnaces were used and temperatures of molten metal often exceeded 2000 degrees Celsius by a significant amount.

Edited By not done it yet on 27/08/2020 08:21:15

Would 7075 and 2024 series scrap aluminium be good candidates for melting? I have access to good amounts of scrap pieces of these materials, I know they are unweldable but would they make useable roundstock if melted?

I had a rummage around on the interwebby thing and one thing that was fairly constant was the mention of how casting will lower the tensile strength of these alloys and 2024 is regarded as being moderately machinable so I don’t know what casting will do to that with either alloy .

You could make a test piece up by melting a small amount and cast a small billet - the suck it see approach !

Those alloys will tend to have a T number after then which is the temper, melting will in effect anneal then so you loose the hardness and other properties. If you can get it for free try a small pour and see how it goes

Yes sure will try it out and come back when I have the means to do it (will be a while!) Tried an online search for information on melting these alloys but didn't find much. As you say trying it out is the way to go.

7075 is high zinc low copper and 2025 the other way round. So they both have an alloying element to provide hardening. From a baic casting you get the -0 properties instead of eg -T6 heat treated. So it will have large grain size and the alloying element distributedinto in larger areas both of which make it soft.

From the phase diagram, not testing, you could harden it by holding at 400c for a while to put the zinc and copper into solid soultion and then quench to make them recrystalise throughout giveing a finer grain with inclusions at the grain boundaries which gives strength. It's 40 years since I did my metallurgy degree so can't remember the details.

Hi Chris

Melting these metals you will loose much of the strength of the original
alloy ,as you have found out there seems to be little information out there
on the heat treatment of aluminium.I found these two books from
Camden were most useful ,the book on the left has 35 pages
devoted to the treatment of aluminium and its alloys ,but just like the
casting will require a lot of time to make up some of the equipment
needed for this .The temperatures needed to do this vary according to
the copper content of the alloy and need careful control for the best results.
These books are still on their listing,the one on the left is the one that
you need.

It obviously can be done the 2 cast turbocharger rotors on the right are in
as cast condition and still have the test marks on the riser .For critical
components like this they are best made from a known alloy, the
milled compressor wheel on the left and the unmachined blank are
2014 t6 aluminium.
My own furnace seen here is a modified Gingery furnace use MPK
bricks built around 1990 , will hold an A8 crucible.

John

Are those compressor wheels your work John? Impressive!

I'm not after having the material properties in as purchased from the suppliers, I know that would be next to impossible to replicate. But if the alloy could be melted into useable bar stock at a considerable cost saving, then why not. For sure I would not use it for something like you're building!

EDIT:

Btw, what do you think of this Jason: https://www.metallab.net/ytongfurnace.php   He is using Ytong blocks for his ovens with good results if used lower temperatures. 

Edited By ChrisB on 29/08/2020 12:10:36

While better than say a dense concrete block they will not perform as well as a vermiculite block or the "wool" mentioned earlier, I think we covered this on an old thread of yours.

However they are cheap, easily available and better than nothing so could be used to make up a simple furnace as in your link, if you are only doing a few heats a year then the extra bit of gas used would still be less than the cost of better blocks. If you find you start to do more billet casting or even get into casting parts then you can get better blocks for the MkII furnace. It could be a false economy to spend out a lot on making an efficient furnace that won't get much use as the money spent on it could go towards buying barstock.

Hi Chris
I was given the cast wheels they are about 56 mm diameter about the
same size used in the Wren 54 turbine engine.

The wheel on the left is for a KJ 66 size turbine and was milled on the Dore Westbury
cnc machine ,seen here was a test cut in wax.

John

Would someone be so kind as to private-mail me a link to the original video which generated so much discussion - just so I can see what generated the big discussion ... thanks - Jann

Hi Jann ,

You have a PM in your inbox .

Well Rob has been at it again and in his latest video he uses an old slave cylinder as a mold - worked well but he used alloy of an unknown grade and although it cast ok it didn’t machine well so his trick of using old mag rims is something one should stick to if they want Bar stock that machines ok .

Surely this is a case of expectation management?

If a bunch of unknown Aluminium scrap is melted the resulting metal won't be to an engineering specification. Unknown composition and not heat-treated to recover properties lost in the melt. Quite difficult to fix in an amateur foundry because few home workshops have the necessary equipment to heat-treat Aluminium - it needs a temperature controlled soak.

Doesn't mean casting Aluminium is a waste of time. Although home-made castings can't be top-notch, could still be fit for purpose. Casting safety critical parts in a shed would be insane, but provided the limitations are recognised, casting Aluminium seems a good wheeze to me. Castings are useful even if they are a bit soft, slightly weak, and don't machine particularly well.

Same objections apply to home-melted cast-iron being a flawed material, but many find that worth doing.

Can't think of a good reason for not trying it.

Dave

I'm reluctant to add anything to what John has said as he has much real world experience and skill in aluminium casting and I have only played around with small castings in brass and white metal.

However, I do understand that most aluminium alloys 'age hardening' at various different rates and some do so at normal temperatures so don't lose heart is a casting appears delicate at first, it may well become stiffer at room temperature on a scale of hours to weeks depending on the mix.

Some types machine better when still ductile, others are sticky like pure aluminium. All I can suggest is that a bit of experimentation may be in order, and if your original source material was nice and hard then the result may well age harden without intervention.

Neil

<edited to qualify that only some alloys age harden at normal temperatures>

Edited By Neil Wyatt on 30/08/2020 11:34:29

Apart from the satisfaction of actually making an ingot of al.alloy, I really cannot see the point. If you want to make something from an al.alloy it might be worthwhile being aware of the difference between annealed and heat treated conditions for two of the materials mentioned earlier

6061 T0 ult. (ksi) 18, yield (ksi) 8, hardness 30 (Brinell No, 500kg load, 10mm ball)

6061 T6 ult (ksi) 45, yield (ksi) 40, hardness 95 (Brinell No, 500kg load, 10mm ball)

7075 T0 ult (ksi) 33, yield (ksi)15, hardness 60 (Brinell No, 500kg load, 10mm ball)

7075 T6 ult (ksi) 76, yield (ksi) 67, hardness150 (Brinell No, 500kg load, 10mm ball)

So, in broad terms the annealed material, apart from being pretty poor to machine would possess approximately 50% of the ultimate strength, 20% of the yield strength and the hardness would be significantly less for both.

Now obviously this will not matter if all you are making is a name plate, but if you are planning to make something strong and light (after all this is what Al. Alloy has been developed for) you may be kidding yourself. No doubt lots of people will chime in with "Well Fred Bloggs made a phoo phoo valve from rescued material, and it works just fine" Well good for Fred would be my response.

cheers, and the very best of luck

Bill

Edited By Bill Pudney on 30/08/2020 12:19:48

Of course you will not be using the cast aluminium for aircraft parts, I would imagine that's clear to all. That does not mean it does not have it's use tho, I normally use aluminium for ease of machining and where strength is not a critical requirement. I have a block of 7075T6 alloy which I use sparingly for special projects. Knowing how expensive the material is I don't want to waste it.

As for heat treating, if you have a pid controlled oven it would not be so difficult to do. Would definitely like to try it out.

The point seemed to be cost saving. For something like an engine bed or just a block to use as a one off jig or arbor this source would be fine.

Chris, this one popped up on Youtube today

Edited By JasonB on 30/08/2020 13:25:08

Yes Jason, that would be similar in principle to what I had in mind and it looks like it works. There are some things I would do differently especially when it comes to electrical safety but the principle is the same.

I had already purchased all the material needed for the furnace quite a while ago to build a heat treat oven. They have sat there ever since collecting dust! A project for the coming winter, summer to unbearably hot here to be spending any length of time in the workshop

One of the channels i subscribe to who has also watched the video on casting has made a video on how he made his funace - Thought it might have some useful info for U.K forum members .