HELP 1

[maherpaul]

What the problem is that we have been told by our supplier
that there is porosity in the base metal and the zinc plating cannot stick to the part it usually take a couple of day for the so called white rust to appear
I have done a Materials engineering degree
but that has been a couple of years back
and i have never be involved in steel or iron manufacturing
when i was taking to the supplier he told that white rust come up after a couple of day after the iron has been plated
this is something that i find hard to believe
is there any exact way of measuring the Porosity
what is basically happening is that we submit plane iron and we get it platted with
Zinc and when we receive the parts there is a white staining on the zinc platting
do you know any way how Porosity can be measured ?
any info would be appreciated

 

[CoryPad]

Your message is confusing, but here are my comments.

1) The white corrosion products are zinc oxide. Zinc oxide forms preferentially to iron oxide because zinc is a more active metal.

2) Cast metals routinely have porosity due to entrapped gas, and this can cause severe problems with coating adhesion.

3) Two simple ways to measure porosity are:

a) measure the volume and mass of a sample and calculate density, then compare this to the accepted density of the alloy

b) cut a cross-section of the part and prepare a metallographic sample. Take a photograph and measure the area of pores vs. area of metal. This ratio is proportional to the volume ratio.

4) A more difficult method to measure porosity is to use radiography (x-rays) to detect porosity in the actual part.

 

[tomwalz]

Contact Ted Mooney
Do a google search for his name.

I think he addressed this from the plating end in one of his columns a while back.

Tom