As a member of the eBay Partner Network & Amazon Affiliate we receive compensation for qualifying purchases

Home /
Search 🔍
the Site
pub Where the world gathers for
plating, anodizing, & finishing Q&As since 1989


E-coat issues when painting welded zinc coated steel

July 1, 2010

I'm welding Galvannealed steel plates of 1.4 mm thickness, which after welding need to be painted by e-coat.

During welding, a thin "white" layer is formed around the seam; then once painted, there are several "yellow stains" which looks like Silicon precipitation issue but in a high amount. My assumption is that this is caused due to my wire filler composition.
Process description is as follows:

100% robotic MIG
Welding type: Fronius CMT (Cold Metal Transfer)
Robots: Motoman
Welding speed: 23-25 in/min
Gas: 100% CO2
Material: 1.4 Thickness, Galvannealed
Coating Layer Thickness: 7 microns
Filler Metal: ER70S6

Does anyone have experience in this issue?, any recommendations to avoid the formation of those "yellow stains"?

Thanks in advance

Alex Heredia
Manufacturing engineer - Stockton, California

Ecoat performance over zinc-coated steels (galvanize, galvanneal) depends on the quality of the phosphate layer that is deposited after cleaning. In order to obtain a good phosphate coating with appropriate crystal size, etc., the welded parts must have a minimum of oxidation and slag. Best performance is achieved when using weld wires with low Si & Mn, which means using ER70S-3 rather than ER70S-6. In combination with the weld wire, the shielding gas should be mostly Ar, with 1-5% CO2 maximum. You also want to minimize the heat input into the weld, so that oxidation in the HAZ is minimized.

Toby Padfield
Automotive component supplier - Michigan, USA
July 6, 2010

(No "dead threads" here! If this page isn't currently on the Hotline your Q, A, or Comment will restore it)

Q, A, or Comment on THIS thread -or- Start a NEW Thread

Disclaimer: It's not possible to fully diagnose a finishing problem or the hazards of an operation via these pages. All information presented is for general reference and does not represent a professional opinion nor the policy of an author's employer. The internet is largely anonymous & unvetted; some names may be fictitious and some recommendations might be harmful.

If you are seeking a product or service related to metal finishing, please check these Directories:

Chemicals &
Consult'g, Train'g
& Software

About/Contact  -  Privacy Policy  -  ©1995-2024, Pine Beach, New Jersey, USA  -  about "affil links"