aluminium body?

**digger** · 17th February 2015, 02:26 PM

Originally Posted by Loubrey

Why...?

Not questioning the advice, just interested why it would be a problem. I have done so for years and not seen any adverse reactions.

Cheers,

Lou

(stolen from elsewhere but I found it interesting!)

Torque Values

If the same materials are being fastened together, then they are assembled dry to the manufacturer's torque values - unless otherwise specified. In critical fasteners such as the axle nut that holds the rear wheel on superbikes, the spec calls for lubricating the threads prior to assembly. The torque spec assumes a lubricated thread. Read your manual.

In general, a thread treated with either an anti-seize or a lubricant requires a lower torque value (than a higher-friction dry thread) to create the same tension in the fastener. So, if you make a modification that changes a component material, such that anti-seize is now needed, you'll need to torque the fastener to a approximately 10% lower value to avoid over-tensioning the fastener (according to Machinery's Handbook, 25th ed.). A new torque wrench is usually accurate to ? 3%.

Galvanic Corrosion

The manufacturer uses a number of different metal alloys, plastics, and coatings - each selected for its cost, weight, strength, appearance, and corrosion resistance among other things. What also needed to be considered, is that when any two different metals touch each other, electricity flows between them (which is how a battery works), and the surface of the metal lower on the list (below) corrodes.

For example, when aluminum or magnesium are in contact with carbon or stainless steel, this galvanic action will corrode the aluminum or magnesium. So the approach is to use steel fasteners to fasten steel parts together, whenever possible.

One problem is that aluminum fasteners aren't very strong, so aluminum parts are held with steel fasteners, but in special ways to reduce corrosion. Carbon steel bolts threaded directly into aluminum is generally avoided for example.

Here's a list of some commonly-used metals. The farther apart (top to bottom) on the list the two materials are, the more corrosion that will occur to the material lower on the list when they are held in contact.

Gold
Graphite
Silver
18-8-3 Stainless steel, type 316 (passive)
18-8 Stainless steel, type 304 (passive)
Titanium
Nickel (passive)
Silver solder
Bronze
Copper
Brass
Nickel (active)
Tin
Lead
18-8-3 Stainless steel, type 316 (active) 18-8 Stainless steel, type 304 (active)
Cast iron
Mild steel
Aluminum 2024
Cadmium
Galvanized steel
Zinc (commonly used as a sacrificial anode in marine environments)
Magnesium alloys

One way to control this galvanic corrosion is to use metals closer to each other in the above list, or by electrically isolating metals from each other. Cadmium plating of steel fasteners for example, is used to reduce the metal dissimilarities with aluminum and magnesium. Paint and coatings are used to prevent metals from touching.

Keeping the two dissimilar metals dry will also slow the corrosion process but just the moisture in the air on a humid day is enough to cause a problem.

Anti-Seize Products

If a fastener won't get disassembled for long periods of time, it's a candidate for using an anti-seize compound during assembly. There are three formulations widely-available based on copper, aluminum or nickel.

The way anti-sieze compounds work is by placing a third dissimilar metal between the two base metals. So the corrosion of a thread in a magnesium part caused by a titanium bolt is reduced by an intermediate copper-rich or nickel-rich thread coating. The aluminum anti-seize compound is for use between (say) stainless steel and magnesium.

The grease in anti-seize products prevents water vapor and liquid water from entering the joint as well, thus preventing galvanic corrosion

**Loubrey** · 17th February 2015, 02:38 PM

Thanks Digger,

I appreciate a bolt that needs specific toque values to work properly would have an issue with a copper grease type anti seize compound due to the reduction of friction, but I don't use stainless bolts on anything that is "mechanically critical".

I've got stainless bolts on the door hinges, bonnet hinges and safari door hinges and I've over the years always used copper grease to avoid bi-metallic corrosion between the aluminium and SS for all the reasons in your post and they work perfectly at that. Where steel plates and Ali meet I use Duralac and I've not seen corrosion in any of those parts either.

Just interested if there is a chemical reason that SS and copper shouldn't be used together as posted by Tombie.

Cheers,

Lou

**Grappler** · 17th February 2015, 06:16 PM

Originally Posted by Loubrey

Swap to stainless bolts where possible and make sure there's no future corrosion...

Cheers,

Lou

Be careful replacing steel bolts, especially in structural parts like door hinges, with stainless
I thought about this but decided against as the ss kits with torx heads are lower strength grade than the steel originals

**Loubrey** · 17th February 2015, 06:45 PM

Hi Grappler,

You're right, the bolts are certainly not as strong as the original steels.

I still however believe they are more than strong enough for the hinges, but I certainly won't use them anywhere near moving mechanical parts and recovery or towbar fixing points.

Add to that the brown streaks of weeping rusty hinge bolts and the SS option is still a good option IMO. Again, I've fitted them to all my UK DEfenders as well as my current one here in WA and I've not experienced any issues with them.

Cheers,

Lou

**JDNSW** · 17th February 2015, 08:00 PM

There are very few places in the body where the lower strength of SS is a concern. This is simply because there are very few places in the body where the required strength is anywhere near that of the size bolts used. Possibly the main bolts holding the base of the bulkhead to the chassis outriggers, and the ones holding the steering column to the bulkhead, but I can't think of any others.

However, as the table in digger's post shows, there are very good reasons for not having stainless steel in contact with aluminium - and using a copper or nickel based antiseize is no help. In marine work, where stainless fasteners and aluminium alloys are extensively used, nylon washers and sleeves are always used to insulate the stainless from the alloy, and this practice should be always followed on Landrovers.

Of course, the hinge bolts are not normally in contact with alloy, although they will certainly encourage the steel hinges and door frames and bulkhead to rust rather than the bolts themselves. But all of these bits are easier to keep a continuous film of paint on, where the bolt heads you can just about guarantee that any paint film will be broken by the tools used to tighten them, and by the threads of the nut.

John

**jackdef90** · 17th February 2015, 08:46 PM

Originally Posted by Loubrey

Why...?

Not questioning the advice, just interested why it would be a problem. I have done so for years and not seen any adverse reactions.

Cheers,

Lou

It CAN cause some form of abrasion, I don't know exactly how I had a chief engineer tell me off once, but at work we generally use molykote on ss , I usually just put a smear of go grease on bolts to stop them from seizing.

**Red90** · 18th February 2015, 02:49 AM

Originally Posted by Loubrey

Agree with the body cappings and bulkhead, but not so sure about the gutters.

I've seen them damaged in the past (roofracks being pushed back through the rear corners) and those were certainly aluminium and part of the roof.

Galvanized steel on mine (1991). I checked with a magnetic before posting just to be positive.

**JDNSW** · 18th February 2015, 05:33 AM

Originally Posted by Red90

Galvanized steel on mine (1991). I checked with a magnetic before posting just to be positive.

Yes. The original 90/110 design had all panels alloy, with galvanised steel gutters, body capping and door trim, inner guards, and ungalvanised steel bulkhead, seatbox, 'C' pillar and sills, and assorted brackets. (Early Series used a lot more both alloy (radiator support, seat box) and more galvanising (sills, door frames in Series 1) but this had already decreased by late Series 3.)

The galvanised door trim was dropped in 1987 when the push button door lock was introduced and the galvanising was dropped altogether in the early 90s.

Through Defender production more and more steel panels have been introduced, as outlined in earlier posts.

John

**Loubrey** · 18th February 2015, 10:38 AM

Magnetic check and confirmation as well:

2010 Defender

Bulk head - Steel
Doors - Steel
Safari Door - Steel
Hinges - Steel
Body Capping Steel
Bonnet - Steel

Everything else aluminium. The roof and gutters form one piece (except for the obvious joints) and is fully aluminium. As per my previous post I was pretty much sure the roof gutters on '96 and '98 Defenders were aluminium and I've just confirmed it on the 2010 as well.

They must changed the roof design for the 300Tdi if a 1991 still has steel gutters. Back to confusion about rust in the gutter of a new Defender...?

Cheers,

Lou

**Laurie 123** · 5th February 2019, 11:55 AM

Originally Posted by Wildduke

Which defenders had an aluminum body? I know the series 3 had an aluminum body, does any of the defenders?

Hi there i have been checking on this one myself.The component is actually called BIRMABRIGHT (AA5152) which is a combination of other metals but basically Aluminium same as the ALCOA truck wheels The later models is still Aluminium but not as strong as Birmabright. This applies to ALL land Rovers

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