Yellow zinc passivation of steel

[dsb]

Cars' monocoque body construction are primarily welded. Galvanized steel doesn't weld. Post weld galvanizing produces too uneven coating thickness to support automotive class A finish, notwithstanding poor paint adhesion to zinc. Also, its a time consuming process requiring inspection: expensive.

On example posted, as described it is a chromate conversion coating. This is one of the most common coating on formed and stamped sheet metal chassis components, others being "Satincoat" (pre-galvanized sheet metal, i.e. all PC chassis) and electroless nickel. It can be a clear chromate conversion, colour is added, usually by default now if not otherwise specified, to visually indicate it's there. For example, a clear chromate conversion coating on aluminum resembles very closely clear anodizing. Where the colour is of interest is that the anodized surface is non conductive.

More than you ever wanted to know about metal coating...

[bulgin]

Hi All

@ auplater

I do seal the things in boiling deionised water for a time equal to the usual 40mins anodising time. I also have acetic acid which I use to adjust the tint ph. I haven't used it in the sealing bath yet. Will try. Thanks

@ steerpike

I never got the black the way I want it. I will soon get the cost lowdown on professional black tint from my supplier as Dylon Ebony General purpose dye doesn't seem to be around any more.

@ Elsewhere in this thread a member mentioned about painting of galvanised steel. I made such a steel fence around 1988. After galvanising, I scoured the lot with coarse rouge and pieces of hessian cloth. What a job

The paint job lasted well more than 14 years without peeling.

Everything is in the preparation.

bulgin