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We have a 7075 Al pump housing that has currently undergone a T651 temper but requires a T751 treatment to alleviate stress corrosion cracking.

Is it necessary to re-stretch a 7075 aluminum part to relieve internal stresses after a T751 heat treatment (Solution heat treated and stretched to remove internal stresses then overaged/stabilized) when a T651 (Solution heat treated and stretched to remove internal stresses then artificially aged) heat treatment was performed just previously?

The part will only be held at minimum over-age temperatures to alleviate SCC in order to maintain most of the tensile and yield strength of the material.

eatscrayons
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1 Answers1

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I am going to start out by saying that aluminum is a mess. There are too many designations and things that you can do to it after it solidifies.

To directly answer your question, what might necessitate an additional round of heat treating is directly affected by the desired final mechanical properties. Each of the designations that you listed is a complete heat treatment. Either one is chosen or the other is chosen, they are not done in a sequence other than what is already defined by the string of numbers.

From the 7075 chart on page 11 of this pdf the only difference between the -T6 and the -T7 is that the -T7 has a slightly better resistance to stress corrosion cracking. If this is what you are looking for, choose the -T7.

The reason that there are so many different alloys and heat treatments is that each combination produces a material with slightly different physical properties.

Properties of the two heat treatments that you listed:

Without very detailed requirements (and lots of experimenting), it is almost impossible to say which alloy and heat treatment of aluminum will be the best for a given situation. You can always go with the most common types.

hazzey
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