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Thread: Do aluminium frames oxidise.

  1. #1
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    Do aluminium frames oxidise.

    Being talked into buying a sub4 (4kg) wheelchair from RGK. Mainly because my shoulders are screwed and getting a 14kg titanium wheelchair into the car has become too hard (not sure what it weighs without spinergy lx wheels with natural fit hanrims and a leather backrest) I doubt below 10kgs. The last time I had an aluminium wheelchair it oxidised and cracked within 2 years of use. So I'm hesitant.

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  2. #2
    Just about everything oxidizes. But the results of oxidation vary from metal to metal. For example iron oxide (rust) is destructive. Aluminum oxide forms a protective layer which strengthens it.

    Cracking of your aluminum frame is probably unrelated to oxidation.
    Last edited by August West; 01-20-2020 at 05:45 AM.

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    Ive had one particular titanium wheelchair for 20 years, and apart from a few scratches, there's no discoloration or any form of degradation. The other titanium wheelchair I use as a daily I've had less than a year has nuts where screws go thru the frame to hold the footplate in place and they are covered in rust holding on for dear life. I'm not impressed at all. the 20 year old wheelchair came from the same company as the 1yo chair. But a change in company ownership has proven to be bad for consumers.
    Everybody wants freedom.... They just don't want it for everybody else...

    A college professor, a man I now consider my dad, once told me...
    "The minute you let someone decide what you can and cannot do, your life is no longer yours." A truer word has never been spoken in my opinion.


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    Aluminum oxidation to the point it effects structural integrity should be very obvious unless it's internal (inside tube). Aluminum is shiny when new, then dulls to light gray with an oxidation patina that offers slight protection.
    If oxidation continues to progress, it will be white and can be felt. This is where the oxidation is eating the aluminum, returning it back to it's natural ore state, just as rust is to steel.

    Titanium is lighter and stronger than aluminum. I would guess your aluminum frame failure was due to stress of some sort or manufacturing flaw that took time/use to show up.
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    Almost all aluminum tubing for wheelchairs should be hard anodized to begin with simply for wear reasons. As noted, aluminum oxidizes to Al2O3 which is actually a good, protective layer and a self-arresting process; unlike rust, it stops after it forms a thin protective layer. Titanium's chief weakness is hydrogen embrittlement which is caused by surface scratches and cyclic mechanical stress. Still very unlikely with the stresses seen by a wheelchair.
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    I thought titanium was heavier than aluminum? Atomically speaking I'm pretty sure it is. Only "lighter" when you use less of it because it's stronger. But when you do that it isn't (much if at all) stronger (depends on alloys being compared) at the same weights. How it's all heat treated really matters too.

    Quote Originally Posted by Gearhead View Post
    Aluminum oxidation to the point it effects structural integrity should be very obvious unless it's internal (inside tube). Aluminum is shiny when new, then dulls to light gray with an oxidation patina that offers slight protection.
    If oxidation continues to progress, it will be white and can be felt. This is where the oxidation is eating the aluminum, returning it back to it's natural ore state, just as rust is to steel.

    Titanium is lighter and stronger than aluminum. I would guess your aluminum frame failure was due to stress of some sort or manufacturing flaw that took time/use to show up.
    Last edited by Oddity; 01-20-2020 at 09:42 AM.
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    Quote Originally Posted by Oddity View Post
    I thought titanium was heavier than aluminum? Atomically speaking I'm pretty sure it is. Only "lighter" when you use less of it because it's stronger. But when you do that it isn't (much if at all) stronger (depends on alloys being compared) at the same weights. How it's all heat treated really matters too.
    Titanium is denser, but much stronger allowing, as you stated, less to be used. Also important is that Titanium tubing is more compliant giving a softer ride than Aluminum. Technically steel can be made thin and flexy too, but the weight penalty is quite high.
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    Quote Originally Posted by Mize View Post
    Titanium is denser, but much stronger allowing, as you stated, less to be used. Also important is that Titanium tubing is more compliant giving a softer ride than Aluminum. Technically steel can be made thin and flexy too, but the weight penalty is quite high.
    my question remains, and has always been, given what I can get off the MDS for annealed (workable) 6al4v titanium vs heat treated 7000 series aluminum, the titanium is ~45% stronger but 60% heavier by volume. How much of that strength advantage is given up to get it down to being as light (or lighter) than the aluminum? TiLite publishes the same weight limits for their chairs of either material so I suspect there is no additional strength given how thin they'd need to make the tube to save weight, but I don't know. I wish there was an independent organization doing destructive and other tests on mobility equipment to cut through the hype marketing BS and end user anecdotes and induction.
    "I have great faith in fools; self-confidence my friends call it." - Edgar Allen Poe

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    Sorry I should have noted the nuts holding the screw which holds the footplate in place has been confirmed to not be titanium. most likely steel (not stainless). Cost cutting measures perfectly exemplified.
    Everybody wants freedom.... They just don't want it for everybody else...

    A college professor, a man I now consider my dad, once told me...
    "The minute you let someone decide what you can and cannot do, your life is no longer yours." A truer word has never been spoken in my opinion.


    Professor Bill Johnston
    (1930- )

  10. #10
    Quote Originally Posted by Oddity View Post
    my question remains, and has always been, given what I can get off the MDS for annealed (workable) 6al4v titanium vs heat treated 7000 series aluminum, the titanium is ~45% stronger but 60% heavier by volume. How much of that strength advantage is given up to get it down to being as light (or lighter) than the aluminum? TiLite publishes the same weight limits for their chairs of either material so I suspect there is no additional strength given how thin they'd need to make the tube to save weight, but I don't know. I wish there was an independent organization doing destructive and other tests on mobility equipment to cut through the hype marketing BS and end user anecdotes and induction.
    My personal experience has been bad with aluminum frames, footrests, and axles. More than one has cracked on me. All positive experience with titanium. You may call that anecdotal and dismiss it.

    But this is supported by the industry consensus that titanium is more flexible and less brittle. Why are you fighting it? If you're waiting for a specific study, you may be waiting a long time. So what are you going to do in the meantime? Are you sticking with aluminum?
    Last edited by August West; 01-20-2020 at 11:37 PM.

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