Strut Tower Bar (am I crazy?)

[fastplant]

I think I"m losing it here. I put in one of those cheapo ebay strut bars for kicks and it was pretty weak (it would bend when you pressed on it). I figured, what the hell, it was cheap. Well, I've had it on for a week now and it gets really hot in there with the engine. I looked at it yesterday and pushed on it and it hardly budged when before you barely had to push on it to make it bend. It's much stronger than it was. Is it even possible that the heat strengthened it? I have to be losing my mind, it doesn't make any sense.

 

[90DSMTurboFWD]

Your losing it.

 

[Nub Styles]

I know that when you heat some metals up to an excessive degree, they do harden. Whether or not this is happening to your strut bar? I really doubt it. The temp. needs to be extremely high, from what I understand.

 

[fastplant]

Originally posted by Nub Styles
I know that when you heat some metals up to an excessive degree, they do harden. Whether or not this is happening to your strut bar? I really doubt it. The temp. needs to be extremely high, from what I understand.

That's what I'm thinking. I'm checking myself into the mental ward now.

 

[Defiant]

You're nuts, but buck-up: strut bars don't get bending load on them anyway. The eBays are fine.

 

[fastplant]

Originally posted by Defiant
You're nuts, but buck-up: strut bars don't get bending load on them anyway. The eBays are fine.

haha, thanks

 

[gaddis]

Aluminum will get harder when exposed to moderate temperatures for extended times. This is called age hardening.

I'm in materials science and I took this from an intro to an old lab.

"The strength of a material can be significantly improved by the precipitation of a finely
dispersed second phase in the matrix. This is accomplished by a solution treatment of the
material at a high temperature followed by quenching. The second phase is then precipitated
at room or elevated temperatures. For aluminum alloys this procedure is usually referred to
as age hardening and is also known as precipitation hardening."


Look it up if you want more info.

 

[tanner261]

Forming a precipitate from an alloy is done when the material is made, not after it has hardened. Heating aluminum will weaken it, grain growth will occur, and it will become more malluable. Heating steel can strenthen it depending on the temperature. It is possible to work harden the material, but I doubt there is enough movement between the struts to do this.

The temps around your strut bar are not high enough to greatly effect the material properties. Yes, the bar is easy to bend when it is uninstalled. Yes, the bar does not bend under a force you can apply by hand when installed, I'm guessing this is what you are describing?

 

[gaddis]

Okay lets try to break this down. There won't be any work hardening because no plastic deformation will occur. The bending that occurs doesn't surpass the yield strain so all deformation is reversible and when the load is removed, it returns to it's original shape.

On the subject of grain size: this is a seperate effect. Yes smaller grains make for a stronger material. Grain growth would definitely weaken it, but the underhood temps aren't enough to cause grain growth in any reasonable time scale.

Precipitation hardening is a different mechanism entirely. I'll use an analogy. Take salt in water these are your two phases in the alloy. When you heat the two up the salt dissolves in the water. This is equivalent to melting the aluminum alloy to make a homogeneous solution. It is then quickly solidified, but the second phase doesn't have time to precipitate out of solution. This takes time and can occur at room temperature. It occurs faster at moderate temperatures, although if the temperature is increased too far the precipitating phase becomes more soluable so you tend to get less precipitation and in larger precipitates. You can also quench salt water by dropping it in liquid nitrogen. Salt gradually crystallizes in very fine precipitates in the ice over time.

However, typically it is neccesary to add stabilizing elements to the aluminum alloy which promote formation of the second phase. These are often much more expensive elements than aluminum. Since these are cheap ass ebay strut bars I doubt that a high enough grade of aluminum would be used for precipitation hardening to occur. So yes, it is possible but in this situation who knows?

If anyone really cares to know, I could sand off a very small sample of my ebay strut bar and x-ray it to see what phases are present and do Electron Dispersive Spectroscopy to determine what elements are present.

It's a strut bar so it really doesn't matter for performance in my opinion, but it's sort of interesting.