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 (http://books.google.com/books?id=Wbwv3nt1gp0C&pg=PA263&dq=aluminum+%22hall+petch%22&num=100&ei=fp3yR_K4G4TazATm-8jmCQ&client=firefox-a&sig=dcsnylRXcHZCoys7lcV8rmp-FaQ) 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.