Aluminum fatigue

Will Subaru's suffer from Aluminum flex in the long run? Hope not:(

 

http://www.leftlanenews.com/2006/01/19/bmw-z8-owners-furious-over-frame-warpage/

 

Thank goodness its just the hood and the trunk lid on the wagon!

^ I dont think it's that much of a problem. The ENTIRE chassis of the Acura NSX is aluminum, all of it, for the past 10+ years. Problem with aluminum is that it's not a commonly practiced metal for body shops, not to mention that it takes a completely different approach when it comes to mending and welding to it. Another thing is that aluminum is lighter, and it's also more "bendable", but if the design of aluminum is correct, it should hold strength (see a lot of cast aluminum wheels for example).

 

Grade of the aluminum (alloy) is also important.

Grade of the aluminum (alloy) is also important.

+1

 

Aircraft grade aluminum alloy is subjected to much higher stresses. Of course it cost more as well. Maybe BMW did not heed their metallurgy research and cheaped out. I have personally handled small scraps of AC aluminum that was almost as thin as those used to make beer cans and could not bend it with my bare hands at all.

^ who do you think you are? the HULK?

Yeah my uncle handed me a piece of a Japanese Zero that had Kamakazied into his battleship and said "See if you can bend it" And I'm thinking "This is a joke, right?" I felt like a dork because it would not bend. Only after that did he tell me what it was.

Wow, i've never seen anything like that.

Um.... we don't have aluminum frames..... so why would Subarus be at risk?

Aluminum is just like any other metal. There are so many alloys that are taylored to the specific application. Just like any other material there can be process defects. Usually the design is done at a decreased yield piont to cover any manufacturing faults.

 

AL is unique in that it can be processed so many different ways and be heat-treated. It's yield does drop as the temp drops and it does not have the fatigue life of steel but, it really is a great material when applied proper.

 

Don't drive your Audi A8 through salt water or in the artic.......

 

Peace,

 

Greg

E-ngineers!

E-ngineers!

 

Yeah? What is your point?

Problem with aluminum is that it's not a commonly practiced metal for body shops, not to mention that it takes a completely different approach when it comes to mending and welding to it.

I remember when the aluminum-bodied Audi A8 came out, there were only something like twelve body shops in the whole USA that were certified to fix body damage on it. You had to take it to one of those shops for body work.

 

Would that be a problem with our LGT's, like if the hood or trunk lid were damaged? I'm thinking not, because those parts would probably just be replaced rather than repaired.

Um.... we don't have aluminum frames..... so why would Subarus be at risk?

 

Um...the fit and finish for one. You have an AL part matted with a steel part in the hinges. I was just wondering if over time the stress at the hinges in particular would cause misalignment.

 

Sounds like it highly unlikey if the AL parts are made correctly. I guess only time will tell. Anybody keeping their Legacy for 20 years

There is no load (at least not significant) at any of the aluminum to steel attachment points. They are talking about stress failure.... frames, control arms, etc. Things that absorb shock, vibration, thermal cycles, .....

 

Not your hood hinge.

Things that absorb shock, vibration, thermal cycles, .....

 

Not your hood hinge.

 

 

Really, last I checked my hood goes through all these. But hey maybe i'm wrong. Engine heat, outside temperature changes, road vibration and shock I guess don't count especially overtime.

 

I'm not saying total failure as in the Audi's but maybe misalignment. Like I said time will tell.

Yeah.... I guess.

 

But I think you are worrying about nothing.

that's really minor considering that a control arm sees WAY more forces upon cornering loads of a car than a hinge on a hood.. besides, you have rubber weatherstrips to soak up the vibration and heat resistant paneling on the underside to keep the temps lower and all that jazz to keep the hood from warping.. besides, the underside of the hood is held up by a structured skeleton.

Perhaps it's also BMW cutting the subframe thicknesses/strength too close as well? If I recall correctly, some E36s (and maybe 46s) have subframe issues as well when equipped with stiffer suspensions.

Aluminum does have a limited lifecycle. In other words, if you subject aluminum to a certain load, it will fail (break) once it hits a certain number of cycles, unlike steel that is pretty much infinite. But with a car, the safety factor is design pretty high so unless you run into something, you will not see loads that will cause the aluminum to fail. The number of cycles will probably never reach a critical level either unless you drive the car daily for like 10 years.

 

Aluminum is harder to work with in certain ways like welding. Tig welding is pretty much a must and it requires a lot of electricity. If you ever see a spot welder for aluminum, you will understand.

scotty, I just forgot, some engines are made of aluminum as well think about that kind of metal technology

 

Last time I checked, I thought our cars use aluminum heads

 

metal quality selection is very important per application. It's the same thing that I am going through right now testing with Racing Brake on Iron alloy for brake rotors.

If you are worry about a car being aluminum, most airplanes are about 70+% aluminum. And most of it is either riveted or glued together.

mccorry I was just trying to shed some light on the subject. Since I have some background in AL I thought it may help. If my reply just said "don't worry about it" with out any explaination would that help more?.......

 

AL's life-cycle is because it is considered notch-sensitive. Meaning that cracks spread easily, once they form. The alloying design keeps them from forming in the specific application.

 

Peace,

 

Greg