Where the
world gathers for metal finishing
Q&As since 1989


-----

Alkaline Resistant Coating for Aluminum 6061

I am designing a part that will be exposed continuously to a high-concentration alkaline solution (> 12 Molar).

The part will be excessively heavy if I fabricate it out of stainless steel, so I would like to make it out of aluminum, with an alkaline resistant coating. Any ideas?

Thanks!

Steve Dayton
- Berkeley, California, USA
2005

---

Dear Steve Dayton,

Your aluminum alloy 6061 is a wrought alloy and it is excellent for anodized coating . but if your alloy is 99.5 %pure aluminum you can make an enamel coating with suitable conditions . and the enamel coating very good as chemical resistance.

Thanks,

Aly Gomaa
- Egypt
2005

---

If your part is not intended to flex or distort apreciably, then electroless nickel high or low phos, 0.001"-0.002" thick will do a great job if properly applied. It is excelent for severe alkalinity but has low elasticity. Has to be inspected for imperviousness (pores, cracks, voids, etc.) before putting into service.

Guillermo Marrufo
Monterrey, NL, Mexico
2005

---

Anodize will seriously degrade in an alkaline solution, as will the exposed aluminum. Not a good coating for your indicated application.

I can not offer any solution for you, I am sure someone else here will shortly!

Good luck,

Bill Grayson
- San Jose, California
2005

---

Apply a very light chromate conversion coating and top off with powder coat.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

2005

---

I think that 0.0015 of High P EN will be your best choice, possibly the same amount of boron reduced EN might be better. You will have to specify where contact points are allowed and it can not be a shape where gas bubbles and air from the agitation can be trapped, preventing further plating.

Titanium is a high priced alternative.

James Watts
- Navarre, Florida
2005

Against strong alkalin, like KOH, PFA (One of Teflon Family)coating will be work even though using temperature is 100C. However, you need at least 200 micron (8 mil)thickness of coating.

Masahiko Yamamoto
- Hayward, California
2005

---

Any high nickel alloy will protect your substrate from high caustic environment. Typically the low P EN is designed for high caustic envrionment and the high P EN for acidic conditions. The best information on the use of nickel in this environment is NIDI.

George Shahin
Atotech - Rock Hill, South Carolina
2005