The Al-alloys are classified according to the type of further processing in wrought and cast alloys and in this both groups again in curable and not treatable alloys. In addition, a distinction is made according to their specific characteristics casting, piston, cutting alloys.
All Al-alloys show over pure aluminum increased tensile strength, yield strength and hardness. Also other properties are influenced by alloying additions, such as thermal expansion coefficient, electrical conductivity, resistance and moldability. Aluminium has a melting point of only 660 ° C and with a density of about 2.7 g / cm³ it belongs to the typical light metals. Its chemical stability resulting from a stable closed top layer of the oxide. This top layer can be enhanced by electrolytic oxidation of aluminum (called Eloxal process).
As a basis for Al alloys is usually a pure aluminum with 99.5 % Al . The main alloying elements are Cu, Si, Mg, Zn and Mn. Their effect is already different by nature, but also depends on the nature of their occurrence in the alloy.
Aluminium reacts with oxygen. In this case, a very thin layer of oxide gets formed. Although this layer is only a few hundred µm thick, it provides excellent protection against corrosion. In case of damage, this layer regenerates itself. Aluminium is extremely durable in neutral and slightly acid environments. In environments that are characterized by high or low pH values, corrosion starts rapidly.
Non-curable alloy with 0.6-7 % Mg and 0.2-0.6 % Mn. Increased resistance to sea water. Usage very extensive, depending on the Mg content: for example AlMg1 as pure aluminum, AlMg5 (tensile strength in soft condition over 200 N / mm²) in the automotive and shipbuilding. With more than 5 % Mg there's a noticeable deterioration with regard to processability, weldability, stress corrosion and the otherwise very good anodic oxidizability.
Treatable alloy with 0.4-1.4 % Mg, 0.3-1.6 % Si, and 0-1 % Mn. Medium to high strength, almost as weather resistant as pure aluminum. Good weldability without risk of corrosion in the weld. It has got a very high conductivity in relation to the strength.
Treatable alloy with 2.5-4.5 % Cu, 0.4-1.5 % Mg, and 0.5-1% Mn. High strength, but caused by the Cu content (more noble than Al) sensitive to corrosion.