Low Melting Point Alloy Stains Parts

[FieldsMet]

I have been experimenting with the use of low melting point alloys (LMPA) such as Field's Metal to hold parts during machining operations. The problem that we have run into is that there is a stain on the parts once the LMPA is removed. I have checked with the manufacturer of the alloys to see if there is any flux in these alloys and he assures me that there is none. I assume that this could be the formation of an oxide, but I would be surprised if it is because the temperature that we use is only slightly above 70C (122F).

Does anyone know:
1. what these stains might be,
2. how they can be removed and,
3. what steps can be taken to prevent the staining in the first place

The metal parts that we are using could be anything from steels, nickel alloys or titanium

 

[racookpe1978]

What are the two metals you are using the low melt point alloy between?
What fluid is your coolant while machining? (Or are you cooling with air)?
What previous fluids or metals have been used on that machine?
How are you cleaning the two metals before heating the LMPA?

How clean is the shop around the base plate and the parts?

I'm thinking you have contamination in the air or environment that is reacting between the LMPA and now-hot machined metals, not just those two metals by themselves on a lab-pure chemistry desk in a sterile isolated environment surrounded by an inert gas. Make sense?

 

[FieldsMet]

The shop is very clean.

One metal mounted in the LMPA at a time. Metals can be steels, nickels and titaniums.

The fluid is water based

 

[metengr]

Not enough information to provide assistance. It could very well be that the staining (in association with the area where the LMPA has been in direct contact with the substrate material) is showing mild surface corrosion or etching from either galvanic attack or under deposit pitting corrosion.

 

[EdStainless]

Or it could be related to how clean the parts are before they are mounted for machining.
Does the color show even if you don't machine?
You need to run some trials mounting parts under different conditions and seeing what the critical factors are.

Most shops wouldn't care because the parts need to be cleaned after machining anyway.
A wash and tumble dry (vibratory) might be enough to remove the stains.

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