Deformation Experiment: Learn about Experiment Results & Processes

[disclaimer]

Hi all;

Hope it's the right place to post this, so

I am missing a report from the classes I was absent from and I can't find help anywhere... Here's the result of the experiment:

http://img300.imageshack.us/img300/5452/plasticdeformationjx8.jpg

These are thin pieces of aluminium that had been previously stretched to reach certain lengths (from shortest to longest). Basically this is all I know. I also know that they were put into an oven or furnace for some time (a bit more than 60 minutes), then they were washed in some liquid (chemical substance?), and the result was something like what you can see in the picture. The more stretched a sample was, the smaller grains we can see.

So, could someone name the processes that should take place while carrying out such an experiment? Or maybe someone could post an extensive description of a similar experiment? Help will be greatly appreciated. I'm in a tight corner now, so I am clutching at a straw. Many thanks.

 

[Astronuc]

I suspect the Al samples were etched to show up the grain boundaries.

Drawing and forging at around room temperature, i.e. cold working, increases the dislocation density in a material.

Heating in a furnace will anneal the material such that the dilocations will move and cancel, and atoms will pop back into lattice positions. In some cases, dislocation networks will form new grain boundaries in a process known as recrystallization.

Another aspect of annealing is the promotion of grain growth in which smaller grains grow to larger grains, which depends on the alloy composition, time and temperature.

Is it possible that region with small grains was not in the furnace?

Key-to-metals is a good site for references on metallurgical topics.

Heat Treatable Aluminum Alloys
http://www.key-to-metals.com/Article39.htm

Effect of Aging on Formability of Aluminum Alloys
http://www.key-to-metals.com/Article144.htm