aluminium sand cast DA 601 suffering oxidation

[dogbural]

Hi,

we have parts supplied from supplier who sand cast, heat treated then machined in order.

Once we opened the package, the machined face ONLY turned to black ( i guess this is called oxidation).

What is the possible cause of this? Simply exposed to moisture?

 

[Tmoose]

Looks pretty bad. Does it wipe off, or is Scotch-brite or chemical cleaning needed ?

Is this a recurring problem, or a one time event ?

What aluminum alloy? Are material certs provided ?
Who provides the castings ?

I'd inquire what cutting oil/coolant the machine shop is using, and how the finished parts are cleaned and packaged for shipping.
I think their process needs to change.
Is the package well sealed?
Does it travel on an open truck, in a fog of exhaust from a poorly tuned gasoline or diesel engine ?

where are the parts shipped from and to?

Pease describe the packaging.
Wrapped in VPI paper, or any desiccant in the box ?

 

[btrueblood]

Tmoose, he says DA601 in title, apparently an Australian spec (US equivalent is 356 cast aluminum). It's not necessarily oxidation, though it may be one cause. Can it be wiped off? If not, google "etch smut on aluminum" for causes and treatments.

 

[EdStainless]

It sounds like one of your QA people should pay them a visit to assure that the cleaning and packaging are what are required in your specifications.
Then again if you didn't specify anything then this is what you get.

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P.E. Metallurgy, consulting work welcomed

 

[dogbural]

Thanks all,

1. This issue is the first time happened.

2. Parts are packed in foam sheet - no desiccant or VIP paper

3. Parts were delivered by sea

4. We have to polish the surface using emery paper

4. What is the common process/way to clean the machined aluminium sand cast?