6061 stress relief time
6061 stress relief time
(OP)
We have an aluminum welded structure consisting of .38 6061 plate with 3x3x.38 angles on one side for stiffness. This assembly will typically be used as part of a mold in an oven operating at 415°F for 3 hours, then cooling for an hour to about 300°F. At this point it is taken out an air cooled with fans. With the residual stresses in the weld as well as the stressed due to the thermal cycling welds will often crack. I found the stress relief temperature for aluminum to be 650°F, but our ovens will only do 550F. My thought is to reduce the residual stress by heat soaking the part at 550°F. My question is will this method work and how long do I need to soak the part at 550°F to get an effective stress relief.





RE: 6061 stress relief time
Shannon Mafodda
www.cryogen.com.au
RE: 6061 stress relief time
Could you please explain in technical terms how cryogenic processing affects the micro-structure of aluminium alloys? I have gone to your website and find very little hard data on aluminium alloys. I am specifically interested in clarification of the following statements:
Thank you for your time.
Nicholas J. Enright
RE: 6061 stress relief time
RE: 6061 stress relief time
As to your second question, of course there could be micro cracks due to welding. Again, these would presumably propogate during stress relieving and could be repaired afterward.
RE: 6061 stress relief time
Perhaps you can use one of the lower strength weld filler metals that would have increased ductility, and better accommodate residual stress from welding. You might be able to eliminate this problem without even having to perform a separate post weld stress relief.
RE: 6061 stress relief time
The web site below is one that I had found regarding improved dimensional stability of 6061 plate. The process is to cycle between low temperature (liquid nitrogen)and moderate temperature to improve dimensional stability. Besides this web site, several others popped up with similar but unexplained results. There was nothing mentioned about increased strength only improved dimensional stability by reduction of residual stresses. Some interesting reading anyway
http://www.noao.edu/ets/gnirs/SDN0013-07.htm
RE: 6061 stress relief time
svanden
RE: 6061 stress relief time
I used a bit different procedure to anneal 6061.
To full anneal:
Heat to 775°F hold for 2-3 hrs depending on size and cool @ 50°F/Hr until 500°F.
To just remove cold work heat to 650°F for 2 Hrs then air cool.
RE: 6061 stress relief time
The reason their isn't any hard data with relation to stress relieving of aluminium and aluminium alloys on my site is that there hasn't been any conclusive studies to definitively explain the results of the process with this type of material. We have relied on our field testing do develop our results (hence our statement), and from experience the process works very well. Its not a miracle cure-all but it does work, remember that commercial cryogenics is still in its infancy and when more technical data is released I will certainly make it available.
Shannon Mafodda
www.cryogen.com.au