WELDING AND HEATREATING OF 6061 ALUMINIUM 2

[rinso]

I HAVE A PROBLEM WITH A MACHINE MADE OF 6061 ALUMIN"I"UM (I'M Australian ). I have had it welded before but it broke again. I believe the material needs to be heat treated when welded. Is this true? If so, how? I am a welder myself, but am not familiar with the material. Any assistance would be greatly apreciated.

Regards
Rinso

 

[Ron]

Rinso...
Most of the 60-series aluminum alloys are very susceptible to weld heat affected zone strength changes. For instance, in the US (using the Aluminum Association as the "code&quot, you must take a significant reduction in the allowable stresses for these alloys within 1 inch of the weld.

There are typically about 7 levels of "heat treatment" for this series from T-0 to T-6 ("dead soft" to strong), plus some variations of each. In the weld area, you don't always know the effect of the welding so if you weld on a T-6 for instance, after welding it might become a T-2 or T-3 or something else, each of which will likely have a lower strength than the original T-6 temper.

The breaking you mentioned could be a result of overstressing, temper change, weld defects, or filler incompatibility. Would need to know a bit more about the failure to offer anything other than the general comments I've provided.

Ron

 

[rinso]

Ron
Thanks for your reply to my query on welding of 6061.
The original failure was certainly stress related due to a seizure in a pivot of the arm that broke. Subsequent failure, ( I believe ), caused by incorrect welding proceedure, unlike filler material, no pre or post heat treatment and fairly high,though normal, stress levels during operation.
Other like machines don't suffer from the same problem so I would like to repair the failure. I can reinforce the repair with fish plates made from 6061 and use same material for filler but still need to follow the correct heat treatment proceedure to be certain of any longevity.
Rinso

 

[gdodd]

To achieve maximum strength out of your welded 6061 aluminium, apply a T6
heat treatment. This calls for solution treating and artificially ageing. For 6061 solution treatment entails heating the part to 500-520 degrees C in a furnace until temperature is equalised then quenching to room temperature. Ageing is then performed again in a tempering or air recirculation furnace for up to 8 hours at 170 to 180 dgrees C depending on desired properties.
See a contract heat treater in your area and he will be able to assist with more information.
Good Luck
also from oz

 

[rinso]

gdodd
Thanks for responding. This is just the sort of info I need.I really appreciate it.
Regards
Rinso

 

[rinso]

Further to this repair.
Is there any preheating or mid weld process that needs to be followed to ensure a good repair before the solution treatment and ageing?
Rinso

 

[gdodd]

If you are having trouble with cracking before using the part then you have a problem as 6061 is readily weldable.
The proposed heat treatment outlined above should be sufficient to produce a sound part provided the weld and materials are the same ie 6061.
You may have a problem with distortion after heat treatment so to counter this talk to a contract heat treater.

 

[Raulz1]

Rinso, Sir;
Setting your torch to a carborizing flame (lots of black smoke) apply a layer of this smoke to the aluminum you wish to treat. Now, adjust the flame of your torch to a normal welding flame and heat the carboned area of the aluminum until all of the carbon deposited on the aluminum is gone. You have heated the aluminum to the proper annealing temperature using this method. Now you can weld it with a torch or arc. I suggest you try this on scrap aluminum so that you get a feel for the process. Good luck.
Raulz1 <turkeynet@peoplepc.com>