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"Chrome Plating on Aluminium"

January 22, 2010

Good day,

My name is Richard, and I work for an engineering company in South Africa. We are finding that there is a need in a number of industries to coat Aluminium. We have several chrome tanks, and use them on standard engineering type pieces (shafts, etc.) I have done some basic tests on trying to coat Aluminium with Chrome using different methods of plating etc. We often get the Aluminium to plate, but our bond is not sufficient. We have tried using Electroless Nickel as a layer between the two, but this would mean setting up a whole new type of plating. The Nickel does work well as a middle layer between the two. I was wondering if there is a way that I can get a layer of Chrome with a good bond to take to the Aluminium, without having to use Nickel as a substrate. I have tried some zincate, similar to that used in Electroless Nickel, but the coating comes out patchy. Our prep is currently a caustic etch followed by a de-smut. Does anyone have any suggestions? Thanks.

Richard Hansen
Coating Sales - Durban, Kwa-Zulu Natal, South Africa

February 2, 2010

Hello South Africa,
The standard procedure for Hard Chrome on Aluminium is the use of a zincate. No intermediate layer required. Etching and type of Zincate would depend on the Aluminum alloy. The zincate does dissolve in the Chrome solution rather fast. My recommendation is to use low concentration of sulfate in the Chrome solution. Enter alive at 2 Volt. Wait for 10 seconds and ramp up current fast to desired current density.
Greetings from Germany

Helmut Horsthemke
- Langenfeld, Germany

February 3, 2010

I agree with Helmut's comments. Zincating aluminum is a very sensitive operation where the time of immersion and the temperature are both important variables. But, the low pH of the chromium solution will dissolve the very thin layer of zinc almost immediately if not covered.

In addition to entering the solution live, you may want to consider a layer of sulfamate nickel over the zincate before chromium plating.

Lyle Kirman
consultant - Cleveland Heights, Ohio

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