Stainless Steel and Anodised Aluminium

[Fred Mundle]

TL;DR Summary

Stainless Steel Bolts in an Anodised Aluminium Block

Hello engineers,

Is it ok to use stainless steel bolts in an anodised aluminium clamp? I know that I should avoid using stainless steel with plain aluminium because of risk of corrosion.

Also, what torque would you recommend that I apply to an M10 stainless steel bolt in an anodised aluminium block?

Many thanks in anticipation...

 

[Baluncore]

Welcome to PF.

What is the anodised aluminium "clamp" or "block" ?
Does it have a thread cut, or a thread insert in the aluminium, or does the bolt pass through to a nut ?

Use silicon grease on dissimilar metal contacts.

What stainless grade alloy is the M10 ?
Who is the manufacturer ?

 

[Fred Mundle]

Hello Baluncore

It's a clamp that attaches a tiller to the rudder stock on my boat, so in use in a marine environment (photo
attached)

Bolt B passes through the clamp to a nut, the hole is not threaded..

The second bolt locates in a thread insert right through the block at C.

There are also grub screws located in threaded inserts in each side of the clamp.

All of these bolts/screws are currently stainless. The bolts are DIN912 M10 socket head screws CH A2, the grub screws are A2 (304), DIN 916.

I do not have any corrosion between the metals at the moment seeking advice to make sure I am doing the right thing?

Also, critically, I have been unable to get any advice on how many Nm I should torque the bolts and crews to. Any advice on that score would be greatly appreciated?

Thank you...

 

[anorlunda]

Use anti galling compound on all contacts between dissimilar metals. Do that anywhere on your boat. Check fasteners on the mast.

 

[Baluncore]

What stainless grade alloy is the M10 ?

Are you in a marine environment with chlorine, or in fresh water? The marks on the head of the bolt will identify the manufacturer and the grade of steel. Then the maximum torque can be found in the tables. Is the bolt a 316 marine stainless bolt or some other type of lower cost stainless steel like 304?

Where a steel bolt is threaded into aluminium, a stainless steel thread insert should be used. That should protect the aluminium surface from physical damage.
https://en.wikipedia.org/wiki/Threaded_insert#Helical_insert

 

[Fred Mundle]

Thank you very much, you've been very helpful

Best wishes..