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Effect of porosity in metal finishing  

March 23, 2009

Dearsir,
I want to know that how does porosity effect in plating/phosphating

Suresh Mishra
technical service - Jaipur, Rajasthan, INDIA

Hi, Suresh. As a matter of semantics, a porous coating means that there are holes in it which expose the the next layer or the substrate to the environment. Your question is too broad for a thorough answer but, briefly, the substrate will probably corrode. And, depending upon the type of plating, porosity can mean that the plating will actually accelerate the corrosion of the substrate due to galvanic potentials. For example, a porous nickel plating on aluminum will cause very rapid corrosion of the substrate.

Regards,

Ted Mooney, P.E.  finishing.com Brick, New Jersey

Of course, if you mean porosity in the casting base material you will have a different set of effects, some of them just as devastating as having porous plating.

You need to be a little less abstract about what you are trying to do.

Brian Terry
Aerospace - Yeovil, Somerset, UK

Exfoliation of copper carbonate occuring on porous tin plating over copper substrate is an example for the destructive effects of porous plating.Porous gold plating increases the contact resistance due to corrosion products of the substrate copper or nickel.Porosity affects both functional purposes as well as corrosion protection.One way of overcoming this problem is to have sufficient thickness of the coating to minimise or eliminate the porosity.
In the case of phosphate coating like zinc phosphating and Manganese phosphating which are subsequently dipped in rust preventive oil for corrosion protection ,porosity may help.
S.Ramajayam

Subramanian Ramajayam     plating chemist Bangalore, Karnataka, India

HI Suresh,
if the parts are porous, more possibilities for corrosion.
to avoid that only we are doing sealent or passivation. if you are not sealing the porous it will get corrode. simple example if you using the parts with out passivation/sealent it will get rust easily.if you are using the parts after passivation, parts will give better life.

Kannan Boopathi
- Salem,Tamil Nadu