effect of delay between solution heat treat and artificial aging 3

[brin]

Is it possible to overage (and weaken) 7075 forged material if there is a significant (eg: 2-3 months) delay between solution heat treatment/quench, and artificial aging to T6 condition? AMS 2770J table 7 note 5 indicates that furnace aging can be started any time after quenching, which suggests there is no delay limit.

 

[TVP]

The ultimate strength is somewhat reduced by extended natural aging (time delay) prior to precipitation treatment. Take a look at Figure 46 on page 185 of the book Aluminum: Properties and Physical Metallurgy by Hatch:

http://books.google.com/books?id=dU...#v=onepage&q=natural aging 7075 delay&f=false

 

[brin]

Thanks TVP. I saw that chart and ordered the book yesterday. Looks good.

So the next question is why is there no time limit between quench and artificial aging in AMS 2770 (or MIL-H-6088). Is there a risk of overaging so that the mechanical properties do not meet 7075-T6 as listed in MMPDS?

 

[brin]

For example- it seems to be an accepted practice to solution heat treat, quench, and form/rework flanges on 7075 extrusions, etc. when they are soft. Then the item may need additional machining, etc. and the aging treatment (to T62 condition per AMS2770) is not completed until several weeks or months after the solution heat treat/quench operation. In the end should we be relying on this to meet the 7075-T62 mechanical properties?