What Is Super Duralumin?
Super duralumin is an aluminum alloy made by adding copper, magnesium, and other elements to aluminum.
It is stronger and easier to cut than duralumin, which is made by adding copper and other elements to aluminum. The hardness of super duralumin is 105HB, whereas that of super duralumin is about 120HB.
However, a disadvantage is that its corrosion resistance is reduced due to the high copper content.
Uses of Super Duralumin
Super duralumin has a specific gravity of about 1/3 that of steel. Taking advantage of its lightweight and high strength, it is used for various structural materials such as aircraft fuselages, bolt materials, and spindles.
Since weldability is inferior to other aluminum alloys, rivets and bolts are often used to join products made of super duralumin. In recent years, welding methods have advanced, and welding joints by resistance spot welding, etc. are used.
Principle of Duralumin
Pure aluminum is an extremely lightweight and workable material, but its disadvantage is its low strength. In general, “the strength of the base material increases when it contains copper. Super duralumin is an alloy in which copper is added to aluminum to improve strength and machinability.
In addition, super duralumin is made by adding copper and magnesium to aluminum. Compared to duralumin with the same composition, the amount of magnesium is increased to further increase strength.
The properties of aluminum alloys are greatly affected by heat treatment. Heat treatment is the process of heating a metal to a certain temperature and then cooling it. The heat treatment symbol T3 indicates that the alloy was cold worked after quenching, T4 indicates that the alloy was only quenched and left at room temperature for about 4 days to age-harden, and T6 indicates that the alloy was cold worked after quenching and then tempered.
The melting point of super duralumin is about 500-650℃, and it can be cast and processed relatively easily.
Types of Super Duralumin
There are three types of material known as super duralumin. Specifically, they are A2017 duralumin, A2024 super duralumin, and A7075 super duralumin. All of these materials are made by adding copper to aluminum to increase strength. They are precipitation-hardening alloys, in which inter-metallic compounds, such as copper precipitate and harden.
1. A2017 Duralumin
A2017 duralumin is an alloy of aluminum with copper and magnesium added. In Japan, industrial production of A2017 duralumin began in 1921 at Sumitomo Copper Works, and the following year, domestically produced duralumin was used in airplane structures.
With a specific gravity of 2.79, A2017 duralumin is characterized by its extremely lightweight, yet excellent strength and machinability. On the other hand, its corrosion resistance and weldability are inferior to those of other aluminum materials. It has the disadvantage of being prone to intergranular corrosion, and its high susceptibility to cracking makes it an extremely difficult material to weld.
A2017 duralumin is manufactured by adding 3.5-4.5% copper and 0.40-0.80% magnesium to aluminum. The addition of copper to aluminum increases its strength but makes it more susceptible to oxidation. The hardness of duralumin increases to 105HB compared to 65HB of aluminum.
A2017 duralumin is used in a wide range of fields, taking advantage of its lightweight and high strength. These include parts for aircraft and rockets, for ships, machine parts such as hydraulic equipment and gears, attaché cases, fastening members such as screws and rivets, and window frames of buildings.
2. A2024 Super Duralumin
A2024 super duralumin is an alloy similar to A2017 duralumin, but differs in the content of copper (3.8-4.9%) and magnesium (1.2-1.8%). It has a higher hardness than A2017 Duralumin, about 120 HB, and its strength increases. On the other hand, corrosion resistance is slightly lower due to the effect of increased copper content. It is also a material with excellent machinability.
A2024 super duralumin has the disadvantage of low weldability. The oxide film on the surface has a higher melting point than that of the base metal, requiring the removal of the oxide film in advance. Another disadvantage is that the heat from the base metal easily escapes, making the welding process unstable.
3. A7075 Duralumin
A7075 duralumin is an alloy of aluminum containing 1.2 to 2.0% copper, 2.1 to 2.9% magnesium, and 5.1 to 6.1% zinc.
It has a hardness of 160HB and is the strongest duralumin material. Its tensile strength is about 570 N/mm^2, which is a significant increase over the 425 N/mm^2 of A2017 duralumin and 470 N/mm^2 of A2024 super duralumin.
Applications for super duralumin include aircraft, rolling stock, and sporting goods. As with super duralumin, its corrosion resistance is inferior, so care must be taken in the environment in which it is used and in corrosion-proofing treatment.