Materials to be used in fins

By "fin", do you mean a "cooling fin" to dissipate heat?
The best material for cooling fins on an aluminum cylinder would be - aluminum.
Aluminum is an excellent heat conductor; it is relatively inexpensive; it is easy to cut and shape; and it can be welded (or soldered) directly onto your cylinder.

I thought a new geometry of the fin and now i want to test it, the best material for the cylinder i found is alumimiun. My intention is to measure the rate of heat transfer throgh the new geometry, it may be cooling also as i haven't decided about it. Ankit Khandelwal( Candle) ********************************* Fortune favours the boldness ***********************************

Ankit, In general, when you are fabricating cooling fins you want to use the best heat conductor you can find. That would be diamond.
But, you also want the fins to also act as a black-body radiator so it can transfer heat by radiation AND by convection. Than means you want something that can be coated black but still conduct heat well. Usually the best cooling fins for electronic devices are made out of copper coated with a black oxide finish.
Unfortunately, it is difficult to attach copper to aluminum. It can be done using various plating and soldering techniques. But, the interface between the aluminum and the copper will not conduct heat as well as aluminum welded to aluminum.
Aluminum (with a black anodized coating) is a good material for fabricating cooling fins. It will give good performance and is relatively inexpensive.
Good luck with your project.

What are i and alumimiun, and why is it the best?

I am ankit khandelwal and aluminum is best because it is thermally conductive and relatively cheap.