Cylinder head failure

[metgeek]

What are the dark areas on the fracture surface of an aluminum die casting?

 

[Pud]

Any pictures? They say a 1000 words.


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[metgeek]

Area of interest is upper left portion below as cast surface. Also, to the left of the tear on the right side.

 

[MintJulep]

They might be carbon.

 

[IRstuff]

The shiny edges of the breaks would suggest that it cracked, and oil, etc., got into the cracks and then the fracture completed and the part broke free

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[Tmoose]

Got any pix of the entire cylinder head ? Engine, air compressor, vacuum pump, or ???

 

[enginesrus]

Areas cracked first and carbon forced in the crack. Anything in that photo looked like shadows from lack of light to me.

 

[metgeek]

Thank you all for the replies.
Apologize for the poor photo of this small piece. I've seen this failure before on a non engine application. It was a structural member that failed exhibiting the dark areas on the fracture surface. It was due to a casting defect from the producer but can't remember what was wrong in the casting process. The producer eventually fixed the problem.

 

[GregLocock]

Sometimes the shiny surface of the grains gets dulled by rubbing as the crack vibrates.

Cheers

Greg Locock


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[swall]

It just looks like the fracture is dirty. Try sticking it in an ultrasonic cleaner for about 30 seconds.