We continue our discussion of aluminum and aluminum alloys by focusing on the individual alloys series. Let’s talk about wrought alloys.

1xxx series:These are the so-called pure-aluminum materials having a minimum of 99% aluminum. They have excellent corrosion resistance, high thermal conductivity and good electrical properties. They are highly workable but have poor strength. Strain hardening can help improve strength somewhat. Iron and silicon are the major impurities affecting corrosion and electrical properties.

2xxx series:Copper is the principal alloying element in this group, often with magnesium as a secondary addition. These alloys are heat treatable. Heat treatment increases strength while lowering ductility. Yield strength is more adversely affected than tensile strength. The alloys have poor corrosion resistance and are susceptible to intergranular corrosion.

3xxx series:Manganese is the major alloying element of alloys in this group, which are generally non-heat treatable. Manganese can only be added to about 1.5%.

4xxx series:Silicon is the major alloying element of this group and can be present in concentrations up to 12%. Silicon lowers the melting point without producing excessive brittleness. Welding wire and brazing alloys are typical applications that take advantage of a lower melting point and good flowability.

5xxx series:The major alloy addition in this series is magnesium. These alloys are non-heat treatable but have moderate to high strength-to-weight ratios. They possess good welding characteristics and good resistance to corrosion, especially in marine environments.

6xxx series:Alloys in this group are heat treatable with silicon and magnesium additions. Though less strong than most of the 2xxx or 7xxx alloys, the magnesium-silicon alloys possess good formability and corrosion resistance with medium strength.

7xxx series:Zinc is the major alloying element in this series and is present at 1-8%. When alloyed with magnesium and/or copper, a heat-treatable alloy can be produced that will achieve a very high strength. Other elements, such as manganese and/or chromium, are also added in small quantities. Alloys such as 7049, 7050 and 7075 are among the highest-strength alloys available. Typical uses include airframes and other structural parts and components that are highly stressed.

References

 2. Substances & Technologies (www.subtech.com)

3. Herring, Daniel H., Fundamentals of Aluminum Heat Treatment, white paper, 2004.