ZAMAK and galvanic corrosion

[vavavroom]

ZAMAK is an alloy commonly used for diecast items. ZAMAK comes in five variants (2,3, 5, 7, HF), and contains slightly various amounts of
zinc (>90% of the alloy)
aluminum
magnesium
copper

I have been wondering about the possibility of galvanic corrosion when ZAMAK is in direct contact with the following alloys: steel, stainless steel, brass

Empirically, in a dry environment, I have not observed any corrosion that I could attribute to galvanic corrosion when ZMAK has been in contact with steel, stainless, or brass. I have however seen diecast zinc deteriorate with visible white oxide buildup and the material getting brittle to the point of crumbling.

I'm sure you want to know why I am interested in this. Since the mid or late '80s, I have built/modified many diecast ZAMAK models that use steel, stainless steel, and brass hardware and parts. I'm wondering if, for example, I should replace stainless steel axles that are in direct contact with ZAMAK.

 

[MasterSolenoid]

I'm no expert, but for galvanic corrosion to occur,
you need three things:
1) two different metals
2) they have to be touching
3) they have to get wet

There is a galvanic corrosion chart that shows all the various metals and how compatible they are with each other.

Galvanic Corrosion - SSINA

When two different metals or alloys are immersed in a corrosive solution or regularly connected by moisture, each will develop a corrosion potential. If the conditions for galvanic corrosion are present, the more noble metal will become the cathode and the more active metal will become the...

www.ssina.com

 

[ls1mike]

I could talk about this all day. If they are not getting wet in salt water I don't think it will be a huge issue for you.

 

[vavavroom]

I'm no expert, but for galvanic corrosion to occur,
you need three things:
1) two different metals

Yes

2) they have to be touching

Maybe not. Supposedly painted components can still suffer from galvanic corrosion.

3) they have to get wet

How wet? Condensation due to temperature changes might be enough,

There is a galvanic corrosion chart that shows all the various metals and how compatible they are with each other.

Galvanic Corrosion - SSINA

When two different metals or alloys are immersed in a corrosive solution or regularly connected by moisture, each will develop a corrosion potential. If the conditions for galvanic corrosion are present, the more noble metal will become the cathode and the more active metal will become the...

www.ssina.com

Yeah, I have seen those charts.

I found an old Matchbox toy car while mowing the lawn. It must have been under a bush for years. which means it was exposed to moisture. Steel axles in an unpainted ZAMAK base. Rusty axles but no crumbling zinc baseplate. In this scenario, the steel should have become the cathode and the baseplate the sacrificial anode. But that did not happen.

 

[wings&wheels]

I'd say you are fine in a household environment. That said, I thought ZAMAK was rather corrosion resistant for every day use? Isn't ZAMAK used for some firearm slides which would be in contract w/ other metals.

Now seeing your wonderful vintage collection, I have wondered if you ever experienced 'zinc pest'?

 

[jhellwig]

Normal household air will not make a sacrificial metal deplete itself to any appreciably degree.

 

[doitmyself]

I. too, have an interest in galvanic corrosion. I have wetted greenhouse cooling pads with stainless steel bolts touching aluminum - no corrosion. I have aluminum quick coupler components screwed onto constantly wet galvanized steel pipe (bare steel threads) - no corrosion after thirty years. I have not witnessed the galvanic corrosion suggested in the charts......... but maybe my data point is very limited.

"ZAMAK" caught my eye. I use IACO brand ZAMAK fittings into aluminum hand-set irrigation pipe.

 

[vavavroom]

I'd say you are fine in a household environment. That said, I thought ZAMAK was rather corrosion resistant for every day use? Isn't ZAMAK used for some firearm slides which would be in contract w/ other metals.

Now seeing your wonderful vintage collection, I have wondered if you ever experienced 'zinc pest'?

Yes, i have encountered zinc pest. It has been limited to some Racing Champion models from the '90s. Crumbling hood and door hinges, some crumbling bodies, and warping and crumbling baseplates. It was probably caused by poor quality casting alloy. It was a random occurrence. I had several versions of the same models and only a few deteriorated. Maybe ten altogether.