heat treat thickness vs as-forged thickness

[kevlar49]

AMS 4141 para 3.3.1.1.2 speaks for an as-forged thickness and a heat treat thickness. What is the difference? Why wouldn't they both be the thinnest direction in the forging?

 

[tbuelna]

kevlar49-

I don't have a copy of AMS 4141, but with your 7075-T73 material there can be reduced mechanical properties through thicker sections. In order to achieve optimum properties after heat treat, it is common to rough machine all surfaces to within a couple mm of the final shape (even die forgings) and then put the part through heat treatment just before final machining. This approach would present the minimum section thicknesses during heat treatment and yield slightly better mechanical properties in the finished part.

I've attached the relevant table from MIL-HDBK-5 showing the reduction in min. mechanical properties for 7075-T73 die forgings versus section thickness.

Hope that helps.
Terry

 

[kevlar49]

Thanks Terry. That does help. Say, would you know the answer to the other question that I posted related to this? Does T7352 impart better dimensional stability after machining than T73? I need to make one 9" diameter forging and one 17" diameter forging. I am wondering if it is better to specify AMS 4147 (T7352) or AMS 4141 (T73).

 

[tbuelna]

kevlar49-

It looks like TVP provided an answer to your question on the other thread, and I would agree with it. The T7352 spec includes a post-heat treat mechanical stress relief, while the T73 spec does not. The less residual stress there is in the part before you begin final machining the less it will move around during/after final machining.

Regards,
Terry

 

[kevlar49]

Thanks! Btw, why is the mechanical working after solution heat treat required? Isn't the aging temperature high enough to relieve stresses?