Blistering during Heat Treatment of AA 6061
Blistering during Heat Treatment of AA 6061
(OP)
Hi,
My company is manufacturing aluminum 6061 forgings (forging temp ~500C). After forging, we are required to heat treat the part to T6 via solutionizing, quench and artificial aging.
One problem we are encountering is blistering at certain locations, blister size approx. 1-2mm diameter. The blisters do not appear at any stage during the forging process, only right after the solutionizing oven.
Do you guys have any idea about the cause of such blisters? I've tried solutionizing in an inert environment (N2) but to no avail. This seems to eliminate the possibility of hydrogen embrittlement from moisture? Could it be entrapped forging lubricants during our forging process within the material, which expands during solutionizing?
Thank you.
My company is manufacturing aluminum 6061 forgings (forging temp ~500C). After forging, we are required to heat treat the part to T6 via solutionizing, quench and artificial aging.
One problem we are encountering is blistering at certain locations, blister size approx. 1-2mm diameter. The blisters do not appear at any stage during the forging process, only right after the solutionizing oven.
Do you guys have any idea about the cause of such blisters? I've tried solutionizing in an inert environment (N2) but to no avail. This seems to eliminate the possibility of hydrogen embrittlement from moisture? Could it be entrapped forging lubricants during our forging process within the material, which expands during solutionizing?
Thank you.





RE: Blistering during Heat Treatment of AA 6061
That is where you start.
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P.E. Metallurgy, Plymouth Tube
RE: Blistering during Heat Treatment of AA 6061
I've compiled some pictures. Here you go!
Just to clarify, the SEM picture on the top right corner shows a cavity rather than blister. It is in fact a protruded blister. It shows a cavity because I have sanded off the blister, exposing the underlying cavity.
Thank you.
RE: Blistering during Heat Treatment of AA 6061
RE: Blistering during Heat Treatment of AA 6061
Could these internal fissures rupture during solutionizing since I am heating up to 560C?
RE: Blistering during Heat Treatment of AA 6061
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P.E. Metallurgy, Plymouth Tube
RE: Blistering during Heat Treatment of AA 6061
RE: Blistering during Heat Treatment of AA 6061
Hy Tan cited the forging temperature of 500C = 932F... which is roughly the solution HT temperature. This seems like an incredibly high temperature for forging 6061 for many reasons.
I would generally recommend cold [AQ or W temper] or warm forging 300-400F... but NOTHING close to HOT forging at 932F.
Regards, Wil Taylor
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RE: Blistering during Heat Treatment of AA 6061
The reason we require 500C (~932F) is due to tonnage being too high if I drop the temperature. 500C is the oven setting temperature. I believe the part cools off by about 20-40C right before forging.
Do you believe the high temperature of forging to be a cause of these blisters? Or would they lead to some other currently unforeseen issues?
Thanks for your feedback!
RE: Blistering during Heat Treatment of AA 6061