The authoritative public forum
  for Metal Finishing since 1989
  

  -----

Experiencing more galvanic corrosion with one grade aluminum than another

2003

I have a problem with galvanic corrosion concerning A356 aluminum. Another material, 6061-T6, is performing much better but it also has different adjoining material. Both are exposed to the same environment - high humidity with possible salt exposure. A356 is painted and the 6061-T6 is unpainted.

Material combinations:

A356 (Base material)
4130 Steel (cover)
8630 Steel (thread inserts into A356)
CRES A286 (fastener)

6061-T6 (Base material)
CRES PH13-8 Mo
CRES A286 (fastener)

What is recommended without changing the base material, A356? Is the insert and cover causing the higher rate of corrosion?

Greg Gaston
Engineer - Pensacola, FL, USA

---

There is less galvanic difference between aluminum and SS than aluminum and CRES. The casting alloy has micro to macro pits in the surface and is a tiny bit lit a sponge. CRES will rust on its own. Paint slows it down, but does not eliminate it.Also you have three different "batteries" in the CRES unit vs two smaller "batteries' in the SS one. Absolutely no surprises with your problem.

James Watts
- Navarre, Florida
2003

P.S.:  OOPS-Foot in mouth. CRES is a SS. What I was trying to refer to was your steel shell to aluminum.

---

You could have the 356 cast aluminum vacuum sealed before installation. This should seal the pores and prevent corrosion.

Don Baudrand
Consultant - Poulsbo, Washington
(Don is co-author of "Plating on Plastics" [on Amazon or AbeBooks affil links]
           and "Plating ABS Plastics" [on Amazon or eBay or AbeBooks affil links])
2003