Fabrikasi dan karakterisasi nano komposit Al-Si-Mg berpenguat Al2O3 dengan variasi fraksi volum 0,5%,1%, 2%,3% dan 5% melalui proses stir casting = Fabrication and characterization of nano composite Al-Si-Mg Al2O3 with variation of 0,5%, 1% ,2%, 3%, and 5 volum fraction produced by stir casting method