I can see a couple of problems here. Maybe my 2 cents for a better result in the future. 1. Try using a different alloy. Al is not really great for detailed castings use zinc (ZAMAC) or if you want to keep using Al use castable alloys. 2. To capture more details use investment plaster or dry wall compound and thinly cover your parts before placing them in sand. This way you will get a hard outer shell capturing more details. 3. Pouring basin with proper sprue was missing, so was a riser and a spin trap. This can in general improve your casting results. Tell me what you think.