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Metal finishing Q&As since 1989


Required Pretreatment before E-Coating on Aluminum

Q. I am working in a CED Paint shop

Recently we got a query for E-Coating on a aluminium die cast part. Want to know what pretreatment process needs to be carried out before doing CED Painting.


Srinivasan Balakrishnan
Employee - Chennai, India
February 22, 2009

A. That is for the person that you are painting it for to determine, or in many cases the OEM that he is building the part for.

James Watts
- Navarre, Florida
February 25, 2009

A. Do non-chrome coating (Oxsilan:Chemetall / Bonderite:Henkel) prior to E-Coat.


March 22, 2009

March 27, 2009
"Phosphating of Metals"
by Werner Rausch
on AbeBooks

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"Surface properties of Conversion Coated Aluminum"
by Raj & Ali

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A. Hi,

Except Degreasing & Phosphating process, the pre-treatment process is almost similar for both aluminium casting & Mild steel components.

Usually, high temperature & strong alkaline Degreasing chemical can cause smut over aluminium components which will affect further Pre-treatment process leading in to quality problems (Poor phosphate coating)


1. Aluminium degreasing process temperature must be lower than the mild steel degreasing stage. Less than 55 °C is preferred for Aluminum casting but 60 -70 °C usually maintained for mild steel degreasing.

2.Degreasing chemical should be weak alkaline, preferably Caustic-free alkaline chemicals recommended for Aluminum casting products, whereas Strong alkaline chemicals are used for mild steel components.

3.Some additives should be added in the Phosphating process while processing the aluminium components.

If you are doing CED coating with any of the job coater plants in Chennai, the degreasing chemical suitability & Phosphate process must be studied. In case if you are planning own facility the ideal process will be

Hot water rinse --> Degreasing --> Rinse 1 --> Rinse 2 --> Surface Activation -->Phosphating --> Rinse 3 --> Rinse 3 --> Fresh DI Rinse --> CED --> UF rinse 1 --> UF rinse 2 --> Final DI rinse


paint shop manager
Chennai, Tamilnadu, India

April 9, 2009

A. Hi,
Usual Pre treatment process for Cast Aluminum is as follows:
1.Alkaline Degreasing (weakly alkaline)
3.Desmutting (usually Nitric Acid)]
5.Non Chrome / Chrome consisting - Chromatizing Process
8.UF rinses
9.Oven Baking
Above process will help you in E-Coating of Aluminum castings, the E-Coat thickness and Baking schedule can be received from your E-Coat suppliers.

Vijaya Kumar Kuppan
- Chennai, Tamil Nadu, India

Q. Why do we do chromotizing on aluminium & phosphating on mild steel?

Viviek Singh
- India
March 27, 2012

A. Hi Viviek.

Metals require pretreatment for a host of reasons including better paint adhesion, resisting filiform corrosion, minimizing galvanic hot spots, etc. The E-coating does not obviate the need for pretreatment.

Steel parts cannot be chromated because chromate will not react with steel; it will not form the required corrosion resisting compounds. Aluminum parts can be phosphatized, but chromate pretreatments are more corrosion resistant.

Please try to flesh out your question with who you are and what your situation is, and we can probably answer more fully and satisfactorily. Good luck.


pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey
March 27, 2012

Q. Which type of reactions take place in degreasing, phosphating and chromatizing process?

Jatin Kumar
- Haridwar, India
April 29, 2012

A. Hi Jatin. The basic reactions in a cleaning/degreasing tank usually involve saponification, wetting & emulsifying, deflocculation, chelating & sequestration, buffering, and inhibition ... for starters. Phosphating creates metal phosphates compounds on the surface of steel parts; they may be iron phosphate, zinc phosphate, or manganese phosphate -- often with additional trace compounds that improve the surface. Aluminum can be zinc phosphated. Chromating forms aluminum chromate conversion compounds on aluminum parts. Each of those topics has been the subject of whole books :-)

Good luck.


pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey

Q. Hi,
I am an E-coater and am having issues with some of our aluminum parts. We run both aluminum and steel parts on the same line. Most of our aluminum (both wrought and cast) come out fine; we only have a few customers that turn out rough. Running about 1-1.5 mils. Does rinse time affect this? Dirty R.O. rinse?

Chris Stebbins
- Spring Lake, Michigan, USA
May 1, 2012

Q. Before E-Coat how you do you remove oil from structure, Mostly for automotive works, specifically in seat structure.

Ananto Saiful
- Detroit, Michigan
May 10, 2012

A. Hi Ananto. Proprietary alkaline cleaners are the most common way to remove the oil. On steel parts you can use strong solutions and high temperatures. If necessary you can add ultrasonics or DC electricity, turning the soak cleaner into an electrocleaner. In that case, scrubbing bubbles of hydrogen or oxygen form on the surface of the workpiece and help to carry away the oil. Good luck.


pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey
May 2014

Process Flow diagram for CED coating on Aluminium substrates

Q. Can I get a CED coating process flow diagram on aluminium substrates. Related specifications. Can any one help me?

Thanks & Regards

Surya Narayana
Process Engineer - Tumkur , Karnataka , INDIA.
May 14, 2014

A. Hi Sachin. Chromate conversion coating.


pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey
April 2015

Cathodic Ecoat on Aluminum

Q. We do cathodic Ecoat on steel tubing. Can aluminum tubing be coated also? What changes would be needed to paint aluminum?

Carl Cusanelli
automotive products - Costa Rica
February 24, 2016

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