T6 Heat Treatment for Aluminum

[psoundappan]

During the T6 heat treatment for the cast 319 aluminum parts the surface darkens and they are inconsistent with each other. We quench the parts in city water and tried several combinations of quench water, increasing/Decresing the hardness, PH level but nothing produced any result.

Do anyone know what causes the parts to darken during the quenching process of the T6?

 

[Nadimuthu]

You must first rule out anything to do with water.Conduct experiments with different water samples.
Also do a macro etch of the component to find out the grain structure.
319 contains 6% Silicon and 4% Copper and segregation can cause this phenomenon.

 

[psoundappan]

In fact I tried quenching them in different water samples and it does make a difference. The water with more crap and high hardness produces a much better surface finish than the fresh water.

The water samples were taked and sent out for further analysis to determine the contents in them. Do you think the use of some kind off quenchents will eliminate this surface discoloration issue?

The Microstructure looks perfect all over the part.

 

[amorrison]

psoundappan: Could you give more details

re: "produces a much better surface finish than the fresh water."

Can the surface be enhanced by addition of particular
chemicals into the water?