Birmabright

[tugboat]

Despite my 1970 2a having been used on heavily salted roads all its life until its engine popped about 20 years ago, and then having been "laid up"/dumped outdoors on the family farm ever since, it has no aluminium corrosion. On the other hand, the 1981 109 SW I bought recently for spares (but may in fact get through an mot) has quite a few pockets of blisters. And looking at Defenders on the road, quite a few surprisingly new ones are riddled with corrosion around this part of the country (wet, salty, west coast of Scotland).

Was Birmabright dropped by Land Rover when the Birmetals company closed up shop in 1980? Apparently, the name covers four possible specs, just to confuse things more (BS5056A, BS5083, BS5154A and BS5251).

Unfortunately, I'm no longer working or I'd have access to an X ray fluoresence gun which simply by pointing at the surface gives a direct readout of the alloy content and then we'd know.

If there actually is a difference, it would be worth knowing when it kicked in if, like me, you're on the look-out for second hand body bits.

[lexi]

Interesting that.

I know the quality of steel itself dropped from early models......especially BL ser 3.

Someone on another forum worked there and the steel supplies changed. Are your blisters near the steel frames?

[tugboat]

Yes, the blisters - not all that bad, to be honest - are generally closer to steel components, suggesting that there's a galvanic driving force. If the later steel grade is more chemically susceptible to corrosion than previously then, even although it will have the same galvanic potential as the original, it will be tending towards sucking electrons out of the aluminium at a greater rate. Hadn't thought of that possibility.

Another factor which may be significant is the paint treatment. The 81 SW has been resprayed, but what appears to be the original finish is peeling in some hidden areas, eg under the bonnet, leaving bare aluminium visible. The old 109's baked finish seems virtually bonded to the metal, almost as good as anodising, albeit it's thin enough to polish through if you're not careful. I guess this was discontinued at some point.

I have to say that I'm very surprised at the state of some 90s and 110s I've seen, now that I've started to pay attention. I get the feeling that the problem has become worse.

[Snagger]

I think the Birmabright was a surface treatment to the aluminium, giving it a goldish colour. The underlying metal is just plain aluminium.

[mickeyw]

The original Birmarbright alloy used in panels of series vehicles is relatively tough compared to say the panels of a 90/110/Defender. Try walking over the wingtops if you want to see the difference in strength. This is the reason my 90 has chequer plate wingtops My old SII and SIII took that treatment without sustaining any deformation!

Quite when they changed the alloy I'm not sure.

The difference in resistance to corrosion is quite apparent too. My 90 is covered in scabs where the paint has blistered, and not necessarily where it is next to steel. My series Landies never had any of that.

[Snagger]

I think that stiffness is due more the aluminium thickness than the alloy grade itself, though that's just a suspicion. The Defender panels are certainly a great deal thinner, though.

[tugboat]

First of all, "plain aluminium", by that I assume the 1xxx grades which have >99% Al, are poor for structural applications. Even these nominally pure forms still depend on small proportions of alloying elements to raise the strength above that of treacle. That's not to say that Land Rover didn't eventually use one of these grades, but Birmabright is definitely not plain aluminium.

Anyway, I've been digging for more on Birmabright. The name covers a range of Al-Mg alloys produced by Birmetals. Two types were used by Rover in body panels, BB2 and BB3. The main alloying element, to enhance strength, is magnesium, 2% in Birmabright BB2, 3% in BB3. In fact, the Al-Mg alloys are typically eight times stronger than a 1xxx series aluminium in its soft condition. BB2 was used in Land Rovers and in a number of panels of Rover P4s, the slightly stronger BB3 in the bonnet and boot of the P6. The current designation of Al-Mg alloys is the 5xxx series. The only spec I can find for BB2 gives it simply as 2% Mg, 0.25% Mn, balance Al, but I expect there are some other smaller traces in it and these could be crucial in terms of corrosion properties. The main features of BB2 and BB3 are: good finish, good formability, good strength, ability to be work hardened (i.e., the metal is further strengthened by being deformed into panel shape), excellent corrosion resistance (including marine applications), resistant to stress corrosion cracking. In short, just what you would want in car body panels! 5251 seems to be the near equivalent current standard alloy but, as I said, those smaller fraction elements in the composition could be important for corrosion and I haven't yet turned up a full spec for BB2.

The key question remains - did Land Rover change the spec of the body materials from BB2 at some time since the Series 2a? Wish I still had access to that XRF gun.

[mickeyw]

Remember than in 1948 Britain had a massive capacity for manufacturing aircraft, which were mostly built from timber and alumium.

When the Rover car company was looking for materials to built their new vehicle steel was in short supply, whereas we had plenty of aircraft grade ally available.

Now I would imagine that materials for aircraft use would have been decent quality, so the corrosion resistance, the stress cracking resistance, and superior strength for its weight of the BB alloys would be ideal. Maybe they were even developed for that purpose, I don't know.

Anyway, we know that Rover found a new application of the plentiful supply of this material in the post-war years.

As for why the spec for LR panels was changed, I think it is fairly safe to say that cost was the major deciding factor. Such as high spec alloy would not have been cheap, and car manufacturers are under increasing pressure to cut costs.

My only surprise it that it took as long as it did for the good quality alloys to be dropped. The quality of chassis steel has certainly had its ups and downs over the years, and well before the end of Series LR production.

[Gazzar]

I can testify to the (variable) quality of the steel - I own a 1981 109!

Front bumper, most out riggers, rear crossmember, and the exhaust hole in the centre rigger all replaced. And a pure b1tch to do - even to get the MIG to weld was fun, I ended up getting the ARC to weld some of the stuff. Still, all good now - replaced with superior britpart stuff (I know, I know), and waxoiled to death.

G.

[lexi]

The yellow passivation was a process done by Landrover. A kit can be bought to do it but quite pricy. Deoxodine cleans the alloy and then Alodine is applied. The finish is permanent.

[tacr2man]

The panel thickness changed somewhere around 90/110 going to defender , my 86 110 CSW is a lot thicker than a 1998 130 DC HCPU that I had for a while . you can walk on wing tops etc . I noticed the external rib roofs are much stronger(less deformation when walking about) than the later smooth roof as well . Still all original doors, and no welding to chassis yet either .