Yellow pasivate wood screws

[TJLinks]

Can anyone tell me if yellow passivate wood screws react with alluminium? We had some stainless screws sent with the roof hooks but we are a few short, the only ones I can find locally are made by Spax (0.94p EACH!!!) and are yellow passivate steel not stainless.
What size/type of screw is everone else using?

 

[Markc]

A2 coach bolt. M8 x 50 or 75mm.

Don't know about the Spax screw. Cost has always put me off them!

 

[TJLinks]

Me too, nearly fell over when I asked for a sample the bloke on the counter said "yeh but I will have to book it out for 94p" for one flaming screw

 

[Worcester]

Try Screwfix - stainless coach screws, our local depot stocks them, our local tool and fixings supplier doesn't !

 

[TJLinks]

Spoke to a fixing supplier today, he said that as the yellow passivate screws are made of steel, they will react with alluminium.. so he said beware and use stainless steel

 

[JulianC]

Are your roof hooks aluminium? Ours are stainless - just assumed they all were!

 

[zeljuga]

Spax screw bay far the best screw on the market, i have been using them four ten years and nothing could compare to it. Al-do use stainless steel version four outdoor use. Yellow will rust definitely with raisin -wood-aluminium-and rain combination.

 

[TJLinks]

Are your roof hooks aluminium? Ours are stainless - just assumed they all were!

We are using Schuco system, Ali slate hooks, approx 10mm thick

 

[MarkieSparkie]

Passivation is the process of making a material "passive", usually by the deposition of a layer of oxide on its surface, created by the spontaneous formation of a hard non-reactive surface film that inhibits further corrosion. This layer is usually an oxide or nitride that is a few nanometres thick.
Your fasteners will be exposed to elements, damp conditions in particular, and any break down of the passivated surface (e.g. through use of tools) will leave the fasteners vulnerable to galvanic corrosion. Although steel and aluminium appear close on the anodic index, there is sufficient potential difference to cause them to fizz in the presence of an electrolyte (water).
In industry in order to raise the potential of steel closer to that of aluminium, the steel is usually cadmium plated and then passivated, cadmium has a near identical anodic index to that of aluminium and thus creates a resistance to galvanic corrosion.
Stainless Steel and aluminium are even further apart (than plain carbon steel) on the anodic index and are therefore an even worse choice, very reactive, and should therefore not be used with aluminium.

 

[hopkins85]

Try Screwfix - stainless coach screws, our local depot stocks them, our local tool and fixings supplier doesn't !

WTF!

Sent from my HTC Desire using Tapatalk

 

[MarkieSparkie]

Further to the earlier post:
On the south coast, we are acutely aware of galvanic corrosion, because salt sea spray in the atmosphere, causes extremely aggressive conditions.
For instance, if we were to use the standard cast aluminium alloy bodied security lights, steel brackets and fixings they would last less than 6 months, by which time they would be reduced to fizzing mass of white aluminium sulphate and rusting steel. The once thick aluminium alloy casting becomes wafer thin and crumbles when touched.
On external work, we generally try to avoid the use of aluminium and its alloys wherever possible, but when unavoidable, we use nylon washers and sleeves on all supplied fixings to minimise dissimilar metal-to-metal contact.