Aluminum and aluminum alloys can be smelted in a variety of different ways. Commonly used are coreless induction furnaces and trough induction furnaces, crucible furnaces and reflective open hearth furnaces (using natural gas or fuel oil combustion) as well as electric resistance furnaces and electric radiation furnaces. Furnace materials range from high-quality pre-alloyed ingots to furnaces made up of low-grade waste. However, even under the most suitable conditions for smelting and casting, molten aluminum is susceptible to three types of adverse effects:
• Under high temperature conditions, the adsorption of hydrogen causes an increase in hydrogen dissolved in the melt over time.
• At high temperatures, the melt oxidizes over time.
• Loss of alloying elements.