Aluminium or magnesium?

[kerryg]

I have to get a bracket welded on a bike I'm doing up. It's the cast bracket that screws onto the bottom of the stanchion (upside down forks), the brake calipers bolt to it and the front axle runs through it. It's only a little job, just re-attaching a little "finger" about a cm square and 6cms long that comes of it, that the front fender bolts onto. Problem is that I have had it welded oncve and it just snapped off again like it was made out of cheese, and now I'm wondering whether it might be magnesium and hence more problematical to weld. Whew!!! Anyway the question is: anyone know a SIMPLE test to identify whether it is aluminium or magnesium? (The Kawasaki people don't know, the forums are no help and I can't find anything on Google...)

Any help appreciated. Cheers

[Pancakes]

So no-one else has light it so I will. Light it! (and have your camera ready incase it is)

[Motu]

Magnesium is a darker grey than aluminium,but you'd something to compare it to....

[marty]

file a little bit off it, onto a piece of paper. light the paper. if it flares off really bright white, it's magnesium.

if it is, bad luck, magnesium is VERY difficult to weld (it tends to catch fire, funnily enough) - which leads to my next point - if there are visible welds on it, then it's probably alloy.

[SixPackBack]

It is probably diecast zinc, or 'shit' metal [as tradesman will know].Do not waste your time trying to repair
Pure magnesium burns under high heat,is expensive to manufacture so i doubt it would be that.
Purchase a new one

[kerryg]

file a little bit off it, onto a piece of paper. light the paper. if it flares off really bright white, it's magnesium.

if it is, bad luck, magnesium is VERY difficult to weld (it tends to catch fire, funnily enough) - which leads to my next point - if there are visible welds on it, then it's probably alloy.

Yeah, that makes sense. I'll give it a try! Not sure if it would be pure magnesium or more likely an alloy ...possibly the latter as I imagine pure magnesium would be very soft. The stuff that we used to set light to in high school chenistry was, anyway.

It's been welded once but the weld wasn't very strong. It is apparently possible to weld magnesium and even to braze magnesium (according to some quick Googling I did), at least magnesium alloys anyway, so that it has been TIG-welded once (a weld which later cracked) is a bit inconclusive.

[Blackbird]

Almost certainly not a magnesium alloy as mag alloy corrodes badly through oxidation. That's why the genuine magnesium alloy minilites on racing minis and crankcases of AJS 7 R racebikes were painted gold to stop corrosion.

And for my next useless fact....

[Ixion]

Almost certainly Dural. Remarkably unlikely to be high Mg .

High magnesium alloy CAN be welded but it's a job for a REAL expert. Might be a handful in NZ, maybe.

Dural should be weldable OK. But weld porosity is always an issue in welding ali. Take it to a GOOD ali welder. And pin the broken off bit.

[kerryg]

Purchase a new one

No, Im 99% sure it's not that that shitmetal stuff. This is off a decent bike (2003 ZX636) and is a substantial and well-made part.

I'm guessing it is probably aluminium but am at a loss to understand why the first repair failed. Might be just poor workmanship in which case another better weld job will do the trick.

As for buying a new one...yeah right!! Too expensive to replace (just under $900) unless I have exhausted all possibilities for repair first, particularly as the damage is a clean break and only to a small bit of the casting that is smaller than my little finger and is not structural.

[kerryg]

Almost certainly not a magnesium alloy as mag alloy corrodes badly through oxidation. That's why the genuine magnesium alloy minilites on racing minis and crankcases of AJS 7 R racebikes were painted gold to stop corrosion.

And for my next useless fact....

Thanks for that and I expect you may be right.

[kerryg]

Almost certainly Dural. Remarkably unlikely to be high Mg .

High magnesium alloy CAN be welded but it's a job for a REAL expert. Might be a handful in NZ, maybe.

Dural should be weldable OK. But weld porosity is always an issue in welding ali. Take it to a GOOD ali welder. And pin the broken off bit.

Thanks. I've got Taylor Automotive lined up to do it up (who were strongly recommended by a bike shop as being good at this sort of work) so we'll see. But when I called them to organise it they said "it's not magnesium, is it?" in a manner which implied it might be a problem if it was, which set me to worrying that it might be magnesium....hence my seeking wisdom from others on this forum. However the consensus seems to be that magnesium is unlikely so I'll press on based on the assumption that it's an aluminium alloy.

Cheers for all the help

[Motu]

I'd go to Machine Part Welding in Penrose - repairing castings is their job,and a lot of places who say they will repair it for you just send it there anyway.

[TLDV8]

I'd go to Machine Part Welding in Penrose - repairing castings is their job,and a lot of places who say they will repair it for you just send it there anyway.

Its not Magnesium... and what Motu said,MPW can repair anything . (fwiw)

[kerryg]

I'd go to Machine Part Welding in Penrose - repairing castings is their job,and a lot of places who say they will repair it for you just send it there anyway.

Cheers for that. I'll check them out definitely

[marty]

Almost certainly not a magnesium alloy as mag alloy corrodes badly through oxidation. That's why the genuine magnesium alloy minilites on racing minis and crankcases of AJS 7 R racebikes were painted gold to stop corrosion.

And for my next useless fact....

if you think they corroded fast - you should see how fast it fizzes (when unprotected) on aircraft engines - hot/cold/hot/cold/wet/dry/hot again....