Pengaruh Penambahan Logam Tanah Jarang (Er) dan Laju Pendinginan terhadap Mikrostruktur (Fasa Intermetalik Beta, Silikon Eutektik, dan SDAS) Paduan Al7SiFe = Effect of Rare Earth Element (Er) Addition and Cooling Rate on the Microstructure (Beta Intermetallic Phase, Eutectic Silicon, and SDAS) of Al7SiFe Alloy