Hello.

I'm making new mufflers from #6262 aluminium alloy. I like them thin-walled, and they are assembled by brazing.
Can anyone say if there is any easy heat tratment for re-gaining the hardness that is lost in brazing. Something I could do at home.

Thanks in advance,

Lauri

Depending on what other metals are in your alloy? one of them ,6061 can be, so maybe your in luck, you can use this technique ,Precipitation hardening, which is also called age hardening , you will need to find the melt point of your alloy, and heat it to just below that point, keep it there for several hours, then after rapid cooling you can put it away for a few weeks while it hardens, or you can heat cycle it many times, 200, 300 and up to 500 degrees. How many depends on your alloy matrix. But it will harden at room temp, just takes a long time
For a muffler I doubt you need this though??
Why not just use 2024 -T351 or  7075 alloy?

Randy

6262 T-6 is generally used for the hardware type screws and nuts. It has lead alloyed into It and is softer. Now you know why it round off so badly. I probably aged a few million pounds of it in my career as we supplied a lot of manufacturers with this alloy. Your right though, the lead makes it easy to machine. There is a slight difference between 6262-T6 and T6511 the most common alloys. I'd be reluctant to offer hardening advise on brazed metal, I'm not a metallurgist.

Below are some mechanical properties of many alloys of aluminum , maybe a help in picking alloys, you can also try to use some Gold Tap magic when you machine al. it makes it easier for me, and you get an excellent finish.  This may come in handy if, you run into problems trying to heat treat  Metal that you have brazed..  Another alloy  may be better suited

Alloy    Temper , Elastic Modulus  - E - (106 psi) ,Shear Modulus- G -(106 psi) ,   Yield Strength(103 psi) ,Tensile Strength (103 psi
-----------------------------------------------------------------------------------------------------------------------------------
1100         10.0    3.75    3.5    11
1100    H12    10.0    3.75    11    14
2014         10.8    4.00    8    22
2014    T6    10.6    4.00    58    66
2014    T62    10.8    4.00    59    67
2017    T4    10.5    3.95    32    55
2024    T3    10.6    4.00    42    64
2024    T4    10.6    4.00    40    62
2025    T6    10.4    3.90    33    52
2124    T851    10.4    4.00    57    66
2219    T62    10.5    4.00    36    54
2618    T61    10.7    4.10    42    55
3003         10.0    3.75    5    14
3003    H18    10.0    3.75    25    27
3003    H112    10.0    3.75    10    17
354    T61    10.6    4.00    36    47
355    T51    10.2    3.80    22    27
355    T6    10.3    3.80    23    37
356    T7    10.3    3.85    21    29
356    T6    10.3    3.85    20    30
5052         10.2    3.80    9.5    25
5052    H32    10.2    3.80    23    31
5056    H38    10.3    3.75    50    60
5056    ANL    10.3    4.00    22    42
6061    T4    10.0    3.80    16    30
6061    T6    10.0    3.80    35    42
6062         10.0    3.75    5    14
6062    T4    10.0    3.75    16    26
6062    T6    10.0    3.75    35    38
6063    T42    10.0    3.75    10    17
6063    T5    10.0    3.75    16    22
6063    T6    10.0    3.75    25    30
6151    T6    10.1    3.85    37    44
7075    T6    10.4    3.90    70    78
A356    T61    10.4    3.90    28    38
D712    T5    10.3    3.80    20    32

Thanks for info. The parts are only end caps for the muffler, they are glued to the center part thats made from good dural tube. So the heat treatment is not highly necessary. However, If there is something I could do to improve it, I'd like to give it a try.
The braze i use melts at around 580c (1076F), sovI don't want to go near that limit in the process and neither do I have an owen where to keep the parts for longer periods of time. But ageing in raised temperature should not be a problem.
So, is there any sense to just make the ageing after brazing (when the parts are kind of annealed)? Should I quench the parts as soin as the braze gets solid.
Sorry, my questions may be stupid.

Lauri

Thanks for info. The parts are only end caps for the muffler, they are glued to the center part thats made from good dural tube. So the heat treatment is not highly necessary. However, If there is something I could do to improve it, I'd like to give it a try.
The braze i use melts at around 580c (1076F), sovI don't want to go near that limit in the process and neither do I have an owen where to keep the parts for longer periods of time. But ageing in raised temperature should not be a problem.
So, is there any sense to just make the ageing after brazing (when the parts are kind of annealed)? Should I quench the parts as soin as the braze gets solid.
Sorry, my questions may be stupid.

Lauri

Hi Lauri
I would have no idea about HT on brazed parts, or for that matter  "glued parts"  will your glue stand heat over 900 degrees? That would maybe be a trail and error deal.
Lyle is the expert , maybe he would have a suggestion.. HT after brazing maybe a tough thing or it maybe would have no affect on your brazed parts, I know i would look for cracks at or near the brazing, especially after quenching and heat treating.
 I have made parts similar to yours, but instead of glue, I used 080 and 256 screws with tiny rounded or countersunk heads, I put them in with RED stud and bearing mount. have ever thought about bolting the parts together?

Randy

Hi Randy.

Sorry, I was unclear. I use brazing to join the header to front cap and exhaust stinger to the rear cap. Those 2 are glued to the center tube which is thin walled dural. Fur gluing I use 7mm wide overlap joint and JBweld and so far they have stayed well together. The first ones (like the one in picture) were assembled weit silicone glue and screws because I was not sure about carbon buildup, and also wanted some adjustability for baffles. Now, When I've found nearly zero carbon inside and finished with the acoustics, I just glue them together. The baffle section is just pressed in the dural tube with interference fit.
So, I forget the HT, maybe it hardens a bit by itself during time.

Lauri

Yes I see the picture you posted,  an nice piece of work.  If you do any HT on the parts, let us know how that worked out.

Randy