(Frequently Asked Questions.)

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Aluminium is a soft and lightweight metal with a dull silvery appearance, due to a thin layer of oxidation that forms quickly when it is exposed to air. Aluminium is nontoxic (as the metal), non-magnetic, and non-sparking. Pure aluminium has a tensile strength of about 49 megapascals (MPa) and 400 MPa if it is formed into an alloy. Aluminium is about one-third as dense as steel or copper; is malleable, ductile, and easily machined and cast; and has excellent corrosion resistance and durability due to the protective oxide layer. Aluminium mirror finish has the highest reflectance of any metal in the 200-400 nm (UV) , and the 3000-10000 nm (far IR) regions, while in the 400-700 nm visible range it is slightly outdone by silver, and in the 700-3000 (near IR) by silver, gold and copper. It is the second most malleable metal (after gold) and the sixth most ductile. Aluminium is a good heat conductor which is why it is used to make saucepans.

Density (near room temp) 2.70 g/cm
Liquid density at melting point 2.375 g/cm
Melting point (660.32 C, 1220.58 F)[1]

Alloys for casting generally have 3-digit numbers. Probably the most common is: A356...Has Silicon as it's major alloying element. Popular for it's strength, it can be easily heat-treated to T6 condition and machines nicely. Still strong in it's as-cast state, it can be a challenge to machine appearing to be relatively "gummy". Use lots of lubricant and sharp tools to get that shiny machined surface. Especially effective is a cutting lube made from kerosene and steric acid melted and poured into the Kerosene while whipping with a paint stirring paddle. Apply to the machining surface with an acid brush. A356 can be anodized however when using colors it can have grey spots.

Scrap aluminum can be found in many forms, and all can be melted in the hobby foundry with some success. The best results for casting will be obtained when using scrap that has been cast before. This helps insure you are using a good casting alloy, even though the specific alloy is unknown or guessed.

Targeted FAQ

Dave Rothermel wrote:
Is there any to tell the difference between aluminum and magnesium?
Heated some VW casting up in a brush fire. Had a nice white hot fire.
Clint Driggars wrote:
You can use a drop of HCI (Muriatic acid) from the Pool or Home Center stores. Mag will fizz right away and aluminum will not. Keep in mind zinc will also fizz. but is heavier than mag or aluminum

Rupert Wenig wrote:
A drop of house hold white vinegar will do the same and is less caustic. Clean a spot first to expose clean metal.