how hot need to melt metal
A glory hole provides more than enough heat to melt most metals including copper (1981F), but not iron (2802F) (A list of metal specs) But a glory hole is awkward for melting trash (i.e. scrap metal with paint and key rings.).
Aluminium will melt at around the higher end of the 600 degC. bracket, but if you try to pour it at that temp. you'll fail! A good pouring temp. for aluminium is around 740 degC. but if your casting has very thin sections you will probably need to be much higher than this.