Cold Press Aluminum Plate

[pcschmid]

We are receiving portions of an aluminum 5456-H116 plate (4.00" wide x 0.250&quot that has been pressed to form a Vee shape of 110 degrees. On the external side, where the bending is we are seeing small longitudinal cracks. the engineer from the company providing the plating says this is normal surface irregularities. I, on the other hand, am concerned of possible stress corrosion cracking in the future. However, I have not been able to find "industry standard" for accept/reject criteria of any cracking as part of the fabrication process. Anyone have ideas on where to look?

Thanks

 

[ERV]

pcschmid,

Search this site for info or publications:

http://www.asm-intl.org/

 

[GoodnPlenty]

It sounds like it could be "Strain Age Embrittlement". I am familiar with this in steels and can't tell you where to research in aluminum, although the cause is the same.

Strain Age Embrittlement is a result of cold forming and is related to material properties and bend radius. The material continues to embrittle with age and embrittlement accelerates with temperature. Cracks can form immediatly with sharp bend radius or impact forming.

Approximate test for ductility can be performed by reversing the bending process without material failure. Initial cracking from cold working is normally reason for immediate rejection.

 

[IFRs]

Your plate should bend well if the proper radius was used. A minimum inside bend radius of 5/8" is recommended for 5456 H116 in 1/4" thickness.

Note that aluminum plate has very distinctive grain visible on the plate. Your bend should be across the grain, not parallel to the grain.

Sounds to me like you have bad bends that have cracked the outer fibers. I'd get them re-done, especially if they are bent with the grain and are used in a critical appliation.

 

[pcschmid]

Thanks for the info.

I had checked the bend radius of our plates, before I read your posts and found they used a 1/2" bend radius. To me this to one of the reasons for the problem. Although I read in Alum Const Manual that 90 degree bend radius for 5456 H321 is 3t-4t or a minimum of 3/4" radius. My copy is from 1969, so the rules may have changed or the temper does make the difference. They did not list H116.

Also, they are using flat bar and not cut plate, my mistake. They are bending the flat bar parallel to the grain. In discussions with others in my field I believe I am on pretty strong ground to reject.

Again, Thanks to all.