For making a alloy sample of 25 gram calculate from the %wt

in general metallurgical practice, the alloying elements must be in the range of 2 to 8 % depending upon the type of alloys. let us consider, if you are preparing 25 gm alloy mass you, you have to take 23 gm of pure aluminium metal in a pre-cleaned graphite crucible and it is allowed to gradually heating. When the mass started melting, you add 2 gm of (for 2% allowing element) silicon oxide and it is stirred to get homogeneous mixture. 

Note : this silicon aluminium alloys is for high performance anode preparation.

Thanks Dolli, I meant it to be prepared by powder metallurgy method and not to be stir cast . Any suggestions in that direction?

This is a good example for you to prepare Al matrix composite by powder metallurgy method:

https://www.researchgate.net/publication/314276639_A_deformation-processed_Al-matrixCa-nanofilamentary_composite_with_low_density_high_strength_and_high_conductivity