T6 or T651

[kevlar49]

6061 T651 is used to minimize distortion after machining vs T6, but when is it truly necessary. I am assuming that if you have a small diameter and very little machining to be done that the residual surface stresses make a big difference, but does anyone have a rule of thumb for what diameter and/or amount of machining warrants T651 to avoid problems?

 

[jfengmet]

T651 is a stress releive after solution treating by stretching. End user must request this to be done based on part geometry and the amount of material to be removed during the machining process. I have seen very few parts that require 6061 T651 as compared to 7075 T7351 which I see all the time.