heat treating aluminium

[Tim Mackey]

Having read a little on treating aluminium, I'm now suffering information overload.

Basically, I have used "technoweld" to add a length of aluminium strip to the front forks of my new nosewheel strut on my PC9. The job seems to have gone well, but does seem to have softened the previously quite hard original aluminium piece. After using the technoweld I left the work to cool naturally, rather than rapid quenching, as this is the recommended procedure for the "weld".

However, researching further, it seems the metal itself may need heat treatment in order to re-harden - but there is so much confusing info out there, and it differs depending on the alloy composition too. I have no idea what the make up of the original material was, other than it seemed pretty darned hard.

So, my question is - should I heat and quench the finished job now?

if so, to what temp? ( I have an infra red temp gun )

....and quench in what - ambient temp water I assume??

 

PS I am unlikely to see any replies to this for a while, so it may be some time before I acknowledge any response

[Olly P]

Tim, yes it will depend on the original alloy of the ali, if it was steel i could offer more detailed advice, but for ali, i would suggest maybe heating until yellow hot and then quenching in water, or light machine oil if you have enough....

 

Olly

[Myron Beaumont]

Timbo

It really does depend on the alloy of aluminium you have .There are so many around,from pure ali to the likes of duralumin and others .

Really helpful eh ! I'm sure you'll find more informative responses from "them as knows" about these things .What I do remember doing ages ago on more or less pure ali was to soak it at a temp that soap smeared on the surface turned black & then plunge into water but on reflection I think it was to normalise the material after bending / work hardening .

[Bob Cotsford]

I'd be very wary of trying to heat ali until yellow hot, in my experience it tends to go from solid to liquid without warning. Quenching, as Myron said, is for annealing ali. I alwayds used the soap trick when kaking m/cycle mudguard stays, then let it work-harden of it'ds own accord. IIRC, the alloys we used tended to harden naturally over time, the annealing had only a temporary effect. That was all a number of decades ago, so my memories may be a little fuzzy.

[Alan Cantwell]

easier to read this than go through it all

[Peter Miller]

Yes, Even dull red is beyond melting point for aluminium.

 

Aluminium does not reharden with heat treatment. IT can work harden but that is nt the same thing.

[Brian Parker]

Depends, but this has worked in the past..
Harden by boiling in a pressure cooker (above 115 degrees) for five hours.

Or try age hardening by resting for 5 days (the aluminium that is, not you).

[Malcolm Fisher]

Many aluminium alloys are "age hardening". After annealing, just leaving them at room temperature for some time restores the hardness. This can be a matter of hours or days to regain full hardness.

IIRC, the age hardening process was discovered accidentally when a heated and quenched piece of metal was found to be soft and discarded. It was tested again some days later when it was found to be much harder than it had been originally.

The method of heating aluminium until a soap covered surface turns black and then uenching in water is the usual method for annealing, and repeats are often required if the metal is shaped by hammering as this work hardens the alloy.

Malcolm

[flytilbroke]

Whatever you do, do NOT try to heat it till it glows as at least raw aluminium melts before that. It is one substance which looks the same hot or cold, solid or molten. Hardening, as you have found, very much depends on the alloy.

[kc]

Malcolm is correct I think, but in addition I have a textbook which says Duralumin "becomes fully age hardenend at room temperatures in 4 or 5 days. Age hardening is a gradual increase in strength but sometimes leads to brittleness"

[Ben B]

The other problem you'll have if you try and anneal it by heating and quenching is the technoweld will melt

[Tim Mackey]

So, still confused

Do I heat it and dunk.

Heat it and cool naturally ( surely this happened during welding anyway ) ?

Or just leave it altogether and see if it hardens.

 

KISS please guys.

[Malcolm Fisher]

Tim,

If I had done your modification, I would just leave the metal as it is. If the aluminium alloy is an age hardening one, the hardness will return with no further treatment.

I think the Technoweld metal has a considerably lower melting point than the aluminium alloys, and if the makers recommend slow cooling I would go with that.

You are right in assuming that the welding process has resulted in heating and slow cooling, and I don't think this makes any difference to the age hardening properties and, in my experience of annealing aluminium in order to shape it by hammering or bending, the hardness has always returned after time.

Malcolm

[Malcolm Fisher]

I should also have said that if the alloy doesn't have age hardening properties, I don't think you will be able to do anything about re-hardening it. Sorry.

Malcolm

[Brian Parker]

Tim, just let it age.
Most common aluminium alloys will temper/harden if left for a period of days.

But maintaining it at just above 100 degrees for a few hours will speed the ageing process to a few hours.

[Tim Mackey]

Ok guys, thanks Ill leave it see what happens

[Erfolg]

I think it is interesting that we all were taught about precipitation hardening Aluminium Alloys, as if they were the most common.

 

Yet move away from the aircraft, weapons industry, these types are not common. The Copper, Zinc and magnesium +silicon are generally considered to be the heat treatable, commonly used in specific fields.

 

I understand that silicon aluminum alloy is the most prolific group. As sand is a cheap alloying material and produces an acceptable product for general use.

 

The manganese aluminum alloy work hardens well.

 

Has any body experienced the effects of cold bending aluminum, being very satisfied with the result. Only to find a day or two later, an orange peel effect as the effect of stress starts to become apparent? Finally surface cracks appeared.

 

I found out the hard way that Cu alloy is quite reactive and corrodes badly, as per brackets on my then car, when exposed to road salt. Yet other grades are very good re corrosion resistance, without anodizing.

 

I guess the problem we have in modelling is that we do not know what grade the alloy is, not even knowing if it is in a group. One of my bikes you 6000 alloy, it tells you on a sticker. Buy a blank from MS, who knows?

 

Oh, I agree with those who advocate soap, as an indicator, that you have got the material to a reasonable temperature.

 

It is worth remembering that some grades of aluminum cannot be welded, as the whole area turns to sludge and runs away. So those comments made about care at high temperature can be very valid.

 

Yet We all seem to acknowledge it is an incredible versatile material, but not always.

[Erfolg]

I have just read the heading again "should i quench".

 

In steels we often quench to stop the steel which has been heated to red hot in its heated phase. The quenching prevents a phase change (atomic structure).

 

Again with steels when heat treating, it is often done to limit the extent that the material changes to its original phase (structure), being both "temperature and time related".

 

When annealing or stress releaving, we are undertaking something similar, which probably does not involve a phase change, but is primarily about allowing the materials structure to achieve an "energetically favorable condition". Which was a fancy way of saying, allow boundaries to move and grains to grow or realign. The underlying message of all of this it is all about energy, related to temperature and time.

 

I think you either wish to stress relieve, or anneal aluminum. As with steel, quenching is meant to arrest/stop further grain growth. If the grain gets large the material will possibly not exhibit the characteristics you probably want, being ductile etc.

 

A slight complicating issue is that there are some grades of aluminum that can be air cooled, and still retain many of the properties generally wanted. Just as adding some alloys to steel, change the "cooling velocity profile", to allow less aggressive means of cooling, yet still retaining the structure wanted.

 

In short I would quench and then try and judge, if I (think I) have achieved what I want.

 

Could you not have a CF undercarriage?