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Solutionizing and heat treatment rob aluminum's luster

We are into Aluminium products for Automobile segment. Parts are made up of AlSi alloy with silicon ranging generally 11~13%, through gravity die system and are subject to solutionising T6/T7 and heat treatment. What we observe that after solutionising and heat treatment, we loose luster on parts and parts look dull in appearance. We want to improve finish without loosing physical properties and hardness.
Pls. advise us for improving the finish.

Mukesh Kumar
- Punjab, INDIA
2005

Use a vacuum furnace.

Guillermo Marrufo
Monterrey, NL, Mexico
2005

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2006

What type furnace are you using? A direct-fired furnace should not be used for aluminum due to excessive oxidation and discoloration from the products of combustion.

For bright solutionizing with good temperature control, a nitrogen atmosphere with forced convection can be used.

Ken Vlach [deceased]
- Goleta, California
Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at finishing.com, continue to benefit from.