Defects in aluminum forgings

[AnnyB]

Dear all,

I have AA7075 aluminum forgings in O1 heat treatment. Then they get machined and hardened T6. The initial forging is US controlled after 01 ht but the part can't be US controlled after T6 because of its complex shape. Can defects develop or grow between 01 and T6 heat treatments?

Thanks a lot.

 

[metengr]

In other words, can defects develop after the 01 heat treatment, Yes, because of forging prior to the solution anneal heat treatment. Can defects develop after the T6 aging heat treatment, unlikely. You can perform nondestructive testing after forging and before the anneal heat treatment to ensure forging quality.

 

[AnnyB]

Actually the 01 heat treatment is done after forging.
So do you mean that any kind of heat treatment (01, T6 or other) don't generate defects? Only forging can be the origin of defects?
If so, could defects be acceptable for a class A ultrasonic testing done after forging and then become larger during T6?

 

[metengr]

That is what I stated originally, the solution anneal treatment, 01, is done after forging. There are two types of causes for defects in aluminum, either from casting the original ingot or from forging. Defect growth can occur during the solution anneal treatment because of thermal stresses generated during water quenching. The aging treatment is not likely to alter existing defects.

You need to determine if these are casting defects or forging defects.

 

[EdStainless]

Is there any HT between casting and forging?
Forging can make casting defects grow, and the anneal can also.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[WKTaylor]

AnnyB...

Can we presume that You are addressing a die forging, as opposed to a hand forging or forged block?

What is the: material spec? forging spec? heat treatment spec? US-NDI spec? Fluorescent penetrant spec?

When You first-article test [random-sample] one-or-more rough-machined-HT'ed forgings for chemistry, grain, grain-flow, mechanical allowables, etc... then a lot of Your questions may be answered.

WARNING. A 'first article inspection' to verify quality/properties of the raw forging is an absolute necessity.

Question: Why -T6x... and not -T76x?? Generally 7075-T6x DFs have poor exfoliation and SCC resistance.

Regards, Wil Taylor

o Trust - But Verify!
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[AnnyB]

Metengr,
When you say that defect can grow due to quenching thermal stresses, do you mean that a crack can propagate or is there also a possibility for internal cavities to coalesce or become larger?

EdStainless,
There is no HT between casting and forging.

WKTaylor,
It's an open-die forging, the shape is a thck disc.
Material spec? AMS4126
Heat treatment spec? AMS2772
US-NDI spec? AMS2154
Fluorescent penetrant spec? AMS2645

T6 is to achieve the highest mechanical properties. We have no corrosion issue.

Thanks to all,

 

[metengr]

When you say that defect can grow due to quenching thermal stresses, do you mean that a crack can propagate

Yes

is there also a possibility for internal cavities to coalesce or become larger?

No, under your stated conditions.