Aluminium alloy will change strength

[TSN79]

Is it the case that an Aluminium alloy will change strength (yield/ultimate) if subjectet to a varying load instead of a static one? I can't quite see why it should...can someone help me with this?

 

[FredGarvin]

You need to phrase your question a bit better. Are you talking about cyclic loads past the elastic limit? Are you referring to an S-N curve issue? Or are you possible talking about work hardening?

 

[Gokul43201]

I suspect it is the former.

(TSN, you could look up "fatigue" and its origin in the "Bauschinger Effect". )

 

[Gokul43201]

On the other hand, several Al-alloys are strengthened by work hardening...

 

[TSN79]

Well, I have two questions to answer. First, which Al alloy is the strongest, and in what region would the yield/ultimate strengths for this alloy lie?
Second, Is this region the same if the alloy is subjectet to cyclic loads instead of static loads?

On the first question I suspect the combination AlCu4Mg2 is the strongest, but I'm not at all sure...

 

[FredGarvin]

There are so many different alloys of aluminum out there, this is a bit of a tough question to answer.

Of the basic alloys that I am familiar with, 7001-T6 has the highest tensile strength of approximately 97 ksi. 7001-T6 is a zinc-copper-magnesium alloy that is age hardened.

In terms of cyclic loading, this is where you will want to look up an S-N curve for that material. The endurance limit for this alloy is 21.8 ksi which, as shown is for 500x10^6 cycles (infinite life). To answer your question, it will depend on how much load you are cyclically placing on the material. If you are continuously cycling past the yield point, you will strain hardent the material. In that case it will become stronger, but also much more brittle and, obviously, the fatigue life drops.