Rather than further thread jack MP' thread about the effect on Young's modulus of casting defects, I thought it better to start a specific thread about casting in aviation.

Foundry Joe brought up a good point on forging verses casting in aviation...

Foundry Joe:
That is a great question, I spent years tracking down something similar, I could never get my test bars to consistently meet the published values

for A356-T6

Ultimate Tensile Strength Yield Strength Elongation

Typical Handbook 34,000 PSI 24,000 PSI 3.50 %

Handbook values came from ALCOA during WWII and were called out as "typical"

Results reported are actually “what a good foundry can achieve on a good day” not average and definitely not a minimum

These results may or may not have been from separately cast test bars and not excised from actual castings

The lawyers got involved and no company now accepts responsibility for these results due to fear of lawsuits if a design fails

Auto designers decided to find out what they were actually getting in their parts

This data was from excised samples from production castings made at high quality foundries, suspension parts, parts driving down the road

Industry was surprised to see huge scatter within part and across parts

Strength is pretty good, buy look at elongation as high as 17% and as low as zero….porosity, oxides and shrink are killers for elongation and fatigue strength

That is why forgings are used in Aerospace, no inclusion defects....

Values are approximate

Ultimate Tensile Strength Yield Strength Elongation at Break
Max 51,000 39,000 17%
Avg 41,000 32,000 8%
Min 36,000 25,500 0.7%

So for design Yield strength would be very low after safety factor is allowed, how high would you go - 15,000?

Unfortunately I don’t have YM data, but you would have to down rate, maybe around 25% of the published values?

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Mark added:
Since it came up, in aviation, we require additional factors of safety with castings, due to the inconsistencies inherent in the process.

For example, for a casting used in critical structure of a small aircraft, the requirement 23.651 would require a factor of safety of 1.5, in addition to the standard factor of safety of 1.5 for structural elements. So 2.25x calculated worst case stack up of design loads. At the least, critical castings must receive 100% visual inspection and dye penetrant inspection, plus X-ray inspection of the structurally significant internal areas, with at least one casting load tested to those factors of safety.

That casting factor can be reduced, by testing more specimens to obtain statistical data to demonstrate the actual process used is more robust.

Your original question was of the achieved Young's modulus, and the effect of casting defects on such. In aviation (and I would guess the automotive industry is similar), you normally assume the Young's modulus of the homogenous material, and then insert the worst case (-3 sigma) defects which your process produces into your FEM model, and assess the effect on crack initiation and propagation, rather than assuming a lower Young's modulus and designing with it.

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FoundryJoe added:

Do you have any experience in how 3D metal printed parts are being treated in aviation? What unique defects do have have or are they considered like a forging?

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MP Added:
This is a bit off topic, but why would a forging be more structurally sound then a casting, because isn't the metal that is used in the forging cast at some point. Is it because there is better control of turbidity and inclusions in the casting of the stock used for forging?

Forgive my ignorance, the only way to learn is by asking questions (and failure )