I want a patent abuot alloy of Al + 3%cu.?

Question

just this

Answer 1

That seems to be obvious state of the art, or maybe available already commercially.

"Copper has been the most common alloying element almost since the beginning of the aluminum industry, and a variety of alloys in which copper is the major addition were developed"

http://www.key-to-metals.com/Article73.h...

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Answer 2

You need to ask yourself what is novel about your invention that is not obvious to someone skilled in that field.  If you can answer that, then do a patent search - you can do this online at no cost.  If you find no prior art patents then hire yourself a patent attorney and proceed.