Strengthening In Aluminum Alloys

Rasputin

Hi everyone!

I have a question about mechanical properties of the materials. As I understand, when in metals microstructure the grains size decreases, the mechanical properties increases, specially metals strengthening.
But I have a discussion with one Prof. who says that this is a minor eefect in Al alloys as compare to the steels. In Al only an Orowan mechanism works. In this mechanism, the dislocation bends between the particles leaving a dislocation ring about each particle.

Is he right? Anyone can help me to find the strengthening mechanism in metals.

Thanks a lot.

Mapes

Your understanding is correct; grain size influences yield strength. (Anything that impedes dislocation motion in ductile polycrystalline materials increases strength.) However, perhaps your professor is saying that in a particular alloy, particle strengthening is so effective that changing grain size has little effect. Do you know what alloy he or she had in mind?

Rasputin

He means all kinds of aluminium as compare to steel where grain size have a big influence to its mechanical properties.

Mapes

See here for a brief discussion in the Handbook of Aluminum.

Modey3

Rasputin,

Your professor must be nuts! When grains get down to the sub-micron level grain size most certainly will effect yielding. Dislocation pileup is a real effect and has been observed on TEM. Making blanket statements like that in Material Science is wrong!

modey3

Rasputin

Modey3, Thanks, I got this book and seems very good with good theories and their explaining.