Aluminum castings - Surface color modification after heat treatment
Aluminum castings - Surface color modification after heat treatment
(OP)
Hello there.
I am trying to find out why aluminum castings suffer a color modification on its surfaces after heat treatment (T6/quenching). We use Foseco's dycotes in our dye casting process, and I wondered if these substances would react with the aluminum oxides on the parts surface, therefore generating different oxides (that will bring a different color to the casting).
The coloration is not homogeneous over the castings surfaces - even some cavities that are unreachable by tools and (dirty) gloves have a different color pattern too.
I appreciate any help/comment on the topic.
eSchein
I am trying to find out why aluminum castings suffer a color modification on its surfaces after heat treatment (T6/quenching). We use Foseco's dycotes in our dye casting process, and I wondered if these substances would react with the aluminum oxides on the parts surface, therefore generating different oxides (that will bring a different color to the casting).
The coloration is not homogeneous over the castings surfaces - even some cavities that are unreachable by tools and (dirty) gloves have a different color pattern too.
I appreciate any help/comment on the topic.
eSchein





RE: Aluminum castings - Surface color modification after heat treatment
RE: Aluminum castings - Surface color modification after heat treatment
RE: Aluminum castings - Surface color modification after heat treatment
The surface of any metal being heat-treated should be first be cleaned to avoid unwanted reactions with contaminants. However, some discoloration is typical of diecast Al alloys due to alloy segregation, and it is accentuated by heat treatment.
Re Foseco's Dycote lubricants/dressings for aluminum diecasting: Most contain colloidal graphite and will cause discoloration. However, Dycote 670 contains an aluminum paste and is specifically advertised to produce stain-free castings. Contact Foseco at http://www.foseco.com
What alloy and diecasting process are you using?
A T6 heat treatment is unusual for diecastings: a) solutionizing is impossible for most alloys due to limited solid solubility and b) solutionizing temperatures can cause blistering of pressure diecastings due to gas porosity. Are you perhaps only artificial aging (T5)?
RE: Aluminum castings - Surface color modification after heat treatment
I have had problems with AC2B aluminum alloy and discolored parts.
RE: Aluminum castings - Surface color modification after heat treatment
eSchein