Do aluminium frames oxidise.

[Mutley]

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.

I live near the sea so everything has to put up with salty air.

[August West]

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.

[Mutley]

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.

[Gearhead]

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.

[Mize]

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.

[Oddity]

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.

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.

[Mize]

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.

[Oddity]

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.

[Mutley]

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.

[August West]

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?

[Oddity]

I really don't think frame material matters. I think we mostly perceive what we want to perceive and take material properties from MDS and other industrial applications and errantly apply them to wheelchairs. Especially after we've invested in one type vs another. There are numerous posts here of cracked titanium. Those are anecdotes too. Do you dismiss them?

I'm not 'fighting' anything. I will always question the lack of data, very high pricing, and marketing BS rife in our world without the independent or objective data to back any of it up.

I've had titanium, magnesium alloy, and both 6000 and 7000 series aluminum chairs. (My Marvel was half 7000 and half carbon fiber.) One that broke was the titanium axle plate on my Quickie Ti. It also flexed so badly it could endo on front impacts, the only chair I've ever had that did that. I also had an aluminum shock mount break on a Quickie XTR.

I rode a magnesium alloy chair for 8 years daily and it never gave me a single issue and rolled super smooth.

None of that experience has yet convinced me one material is objectively better than another.

I don't think any of us could tell what our chair was made of if we hadn't been told ahead of time. The differences if any are so subtle as to be mostly psychological IMO. Except the pricing. Those differences are real and not insignificant.

I think the vast majority of the 'this vs that' material debate serves manufacturers way more than it serves us.

At the end of the day I want fit, efficiency, and intelligent design. Material isn't on my radar with the possible exception of the new fully carbon fiber designs (i.e. Panthera X, purely from a transfer weight consideration).

[August West]

Never seen titanium crack. Based on personal experience and what I read, aluminum is worse. While strength is always an important factor, I also consider transfer weight, appearance, comfort, and maintenance.

The chair frame that best meets all these needs for me is the Quickie Titanium. It's survived for 15 years so it's strong enough for me. It's super light (never seen a lighter frame other than the Python) to get in the car. It flexes (some may say too much) so it's comfy going down a road. A quick polish is all it takes to restore it's appearance. It requires no other maintenance. If there's another chair frame that can do all this better then I want it.

[Oddity]

Our experiences are precisely why we shouldn't be left to make decisions based on inferences taken from single/small sample anecdotes and "personal experience". Your favorite chair that lasted 15 years was a Quickie Ti. My only chair that ever broke and dumped me onto the ground, far from home, with no way to even get back to my car, was a Quickie Ti. These are both meaningless and why, as consumers of very expensive medically necessary equipment, the market should demand data and not have to rely on marketing slicks and anecdotes for important purchasing information.


(There are at least 3 threads here of TiLite ZR and TR frames cracking that I found easily, but I'm not gonna link them in because, again, they don't "prove" anything in the material debate. Everything breaks. I'm only giving TiLite the guff because they're the only company left making claims of superior performance using titanium without providing any proof, or even higher weight tolerances or better warranties aka putting their money where their mouth is. I'd love the proof because I'd happily spend more to get more if I KNEW I was actually getting more.)

There are basic "destructive" tests that have to be done as part of FDA approval (Icon shared some film of one of theirs). We should have all this data from all the manufacturers IMO, and then some (independent pushed to the limit data. Maybe I should start an organization to try to do this. Hmmmmmmmm...edit: I suspect they're all so similar it doesn't really matter, relative to the expense of doing it, but I sure think it would help us make more informed decisions.)

[August West]

Can’t disagree with your logic. But don’t hold your breath on the study. In the absence of a study what are you selecting and why?

[Oddity]

I choose my most recent chair because I was curious how close I could get to the fit and performance of my $7,000 Lasher Sport BT-Mg for as close to 1/10th the cost as possible. I choose the BT-Mg because the transfer weight was advertised as less than 10lbs (it was actually 11.5lbs). I bought my Marvel and Icons to support Jeff and Christian's businesses. My next chair will most likely be a Hands on Concepts Rigid Lite (titanium) because I want to support Steve's business and have a chair hand made to my exact specs, welded from one end to the other, for what I consider a very reasonable price.

(My first 3 chairs, all Quickies, weren't so much chosen as they were settled upon based on a lack of awareness, knowledge, and involvement on my part.)

My choices today mostly revolve around doing business with people I respect, economics, and for the chair itself my priorities are fit, efficiency (to include weight and strength to weight), and intelligent designs (including maximizing/exploiting the potentials of whatever materials it happens to be made from.)

To make the most informed and best decision possible I wish I had real data. For the types of $ involved it seems criminal that I don't. I'll complain about this until it changes or I do something about it myself, frankly