What metal is a `74-`76 bumper made of?

[02Nut]

After following this thread for the past couple of days, its kind of interesting how its run its course.

ClayW - the bumpers are aluminum and originally came from the factory with a polished & anodized finish.

From my experience, "clear" anodizing tends to become hazy when exposed to outdoor weathering (i.e. sun & rain). Once the anodizing becomes hazy, there's not much that can be done to "repair" the anodizing except stripping and re-anodizing.

Unfortunately, the re-anodized bumper will again become hazy over time when exposed to outdoor weathering.

Personally, I would carefully strip the anodizing, polish the bumper and apply a clear coat.

[rogerspeed]

Rorshaque (spell checque) this.....Wikipedia sez that they put pure aluminum as cladding on an aluminum alloy substrate. And I have a question pending at 'aircraftspruce.com' they have quite a list of alloys and say that 2024 is for truck wheels. Report follows when (if) they reply.

Blotto, writing checks you can’t cash, “say nothing once, why say it again?” Wikipedia the fount of all knowledge. Any relevance to the bumpers we’re discussing.? Bumpers I’ve removed and weighed, scrapped at a major recycler for kash and examined the severed cross-sectional remains, thereof. Me, can't spell, or type while the checker on this site is balky (it ain’t heavy my brother) so my posts maybe construdal. Meanwhile on the AlfaBB a guy has claimed aluminum is not a metal! Good waders are required serving that periodic table.

[Pinepig]

Rorshaque (spell checque) this.....Wikipedia sez that they put pure aluminum as cladding on an aluminum alloy substrate. And I have a question pending at 'aircraftspruce.com' they have quite a list of alloys and say that 2024 is for truck wheels. Report follows when (if) they reply.

I'm dying here man, don't give up homie, the bumpers may not be aluminum.

[02Nut]

I also doubt that anyone would cover stainless steel! what would be the point and it is way to expensive. And coating or anodizing is totally different from "cladding" there is no aluminum clad steel, regardles of "aluminization"? Anodization is a dying process. I think our big bumpers are polished and then coated with a sprayed on coating to keep the shine.

Mike_R - the anodizing process deposits an aluminum oxide layer onto the aluminum. Decorative anodizing comes out of the "tank" without any color (OK - essentially colorless for 6061 aluminum). Color dyes can be applied to the fresh anodizing to give the anodizing "color". After color dyeing, a sealer is applied to "seal" the color into the anodized layer.

[Guest Anonymous]

I am your rorshack test......your worst nightmare. And apparently you can't take a bit of truth seeking! It is an alloy of aluminum with a coating! Thas good enough for me. The folks at 'aircraftspruce.com' didn't know. They said ask BMW.

[H_Krix]

I could have sworn I said that in the fifth post:

The whole thing is Aluminum (there might be some zinc and nickel in there too) thats been anodized

[rogerspeed]

translation....its actually 'metal' a type of steel that's electrically coated with aluminum. The cleaner is polishing the thin coating of aluminum on the metal bumper. The electrical coating process is called 'anodizing.'

steel this thread and pin a 'metal' of your chest

[Guest Anonymous]

I guess mr. Krix takes the prize. Aluminum alloy, a polished outer surface without cladding, and an anodized but not dyed protective coating. Although we're not sure about the anodized protective outer layer.....it could be naturally forning aluminum oxide. Or/ the polished surface could be spotting with aluminum oxide and creating the haze. I'll guess that buffing with a really light buffing compound would remove the oxide and repolish the alloy's surface.

Therefore, a non etching, supermild buffing compound woud restore the lustre?

Just for giggles there is another source of information that may respond. I'll post his comments if they are forthcoming.

[Guest Anonymous]

Sorry again guys.....I guess I'll beat this one to death. I just looked at the scratch made by the bottom of a bumper of a chev truck on my bumper. It peeled away two layers before it got into the main metal. It looks like a top layer of chrome on top of a layer of copper on top of the aluminum alloy bumper metal. I have heard that it is proper procedure to electroplate copper on top of aluminum as a transition or bonding layer before you plate with chrome. If this is the case, you need a cleaner for chrome not AL.

Anybody got a microscope......

[esty]

got a microscope......

the big bumper used between 1974 and 1976 on BMW 2002's is solid aluminum with an anodized finish

perhaps your "specialty" bumper was made by someone using various other metals

[visionaut]

this has got 2 B 1 of the most crazy FAQ threads eva... ;-)

Big solid alum bumper lover...

[02Nut]

Inkblot86 - Can you post a picture of your bumper? I'm curious to see if you're referring to a US Spec '74-'76 bumper or a Pre-'74 US bumper.

Sorry again guys.....I guess I'll beat this one to death. I just looked at the scratch made by the bottom of a bumper of a chev truck on my bumper. It peeled away two layers before it got into the main metal. It looks like a top layer of chrome on top of a layer of copper on top of the aluminum alloy bumper metal. I have heard that it is proper procedure to electroplate copper on top of aluminum as a transition or bonding layer before you plate with chrome. If this is the case, you need a cleaner for chrome not AL.

Anybody got a microscope......

[Guest Anonymous]

U.S. spec '74-76 bumper

[Guest Anonymous]

sorry guys....I only have a film cam at this time. Maybe I can borrow a friends....I'll post a pix when/if that comes through. Meantime the "plate" thickens .... there is a comment that suggests that the top layer on this bumper is Nickel not chrome. The older bumpers had a chrome exterior and the later big bumper cars have a dull finish even when brand new. The dull finish indicates Nickel not crome and the final top layer. Still trying to get a comment from some Beemer people.

And esty, how can one determine if it is a 'specialty' bumper. Though they're hard to find, I see a couple around. I think is OEM but maybe the PO changed it. I still wonder about the nickel not chrome.........

[Guest Anonymous]

Hear Ye Hear Ye Hear Ye...for Mensa folks, rocket scientists, and other fine folks only:

Regarding the USA '74-76 big bumper the final final final comment is:

Top layer: Proprietary BMW alloy of Nickel, Aluminum and Chrome

Transition layer: Electroplated Copper (Cu)

Casting layer: Aluminum alloy - T6061

There may be bumpers ou there that have had this outer layer stripped and base layer polished as part of a restoration process. Those are considered solid aluminum alloy.