Aluminum Alloys

Although its mechanical properties are lower than those for steel, aluminum alloy has an excellent strength-to-weight ratio, making it suitable for most engineering applications. Alloy densities range from 2,6 to 3,0 grams per cubic centimeter and its strength could be as high as 700MPa after heat-treatment is applied.

In the presence of oxygen, aluminum creates a thin layer of aluminum oxide on its surface that protects it from most corrosion mechanisms.

Compared to other materials, aluminum’s low hardness makes it vulnerable to excessive wearing, especially in applications where it has to be in contact with other materials.

Aluminum is exceptionally recyclable. The energy costs related to aluminum recycling are only 5% of what is needed to make it from bauxite.

Aluminum alloys are used in everyday applications and about 25% of its production is used in the automotive industry, another 25% is used in the fabrication of beverage cans and other types of packaging 15% in both construction and electrical applications, and 20% in other applications.

There are two major groups used to label aluminum alloys depending on how they were fabricated: wrought alloys obtained by forge and work, and casting alloys obtained by metal casting. Their microstructures are considerably different and these major groups can be divided based on the possibility of hardening by heat-treatment.

Strengthening methods of the alloys are also classified using the letters, F for as fabricated, O for annealed, W stands for solution treated, T for age-hardened, and H for cold-worked.

1. Aluminum 2011-T3

Having higher quantities of copper, this alloy has very poor weldability and corrosion resistance but it’s the best choice for a CNC machining process. It is used in the automotive industry, electronic industry, and as a part for clocks and machinery. The surface finishes obtainable by machining are very good and its mechanical properties are relatively high. It also has a very high fatigue strength, which allows it to be used in shafts and gears.

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2. Aluminum 3003-H18

This alloy contains higher amounts of aluminum mixed with manganese and silicon which reduces its strength but enhances its formability, workability, and corrosion resistance. It is used as a machine component in the food industry, pressure vessels, and piping. Compared to other alloys it has low machinability, but this process can still be used to obtain complex figures. This alloy may be coated to improve its wear resistance.

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3. Aluminum 5052-H32

This Aluminum-Magnesium alloy has small quantities of chromium, iron, and silicon. It has been cold worked and stabilized at low a low temperature to augment its mechanical properties. It has a high fatigue strength, very good weldability, and excellent corrosion resistance. The 5052-H32 alloy is used for aircraft’s fuel/oil lines, fuel tanks, and sheet metal applications. This alloy is often processed in CNC machining centers because it has very good machinability regarding its strength.

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4. Aluminum 6061-T6

This alloy is composed by 95,8% to 98,6% of aluminum, 0,8% to 1,2% of other materials such as chromium, silicon, iron, and copper. It’s solution treated, artificially hardened, and used in the naval and aerospace industry for its high strength, corrosion resistance, and its good acceptance of coatings.

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5. Aluminum 6061-T651

Having the same composition as the alloy shown above, the T651 is stretched up to 3% to alleviate the residual stresses left after water quenching, allowing for a further increase in strength. It’s used in the marine industry, hydraulic pistons, pipe couplings, and in the electrical industry for fittings and connectors. Its high corrosion resistance, better strength, and acceptance of coatings make it a great choice for naval purposes.

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6. Aluminum 6063-T6

With a smaller magnesium concentration compared to other 6XXX alloys, the 6063 alloys need to be tempered to improve their mechanical properties. Having a higher amount of aluminum, it has good workability and formability and since the copper concentration is very small (below 0,10%) its weldability is also remarkable. This alloy is used in the transportation industry, it is commonly extruded into railing profiles and pipes and it can be also used in furniture because it allows for a very appealing surface finish.

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7. Aluminum 7075-T6

Composed by considerable amounts of magnesium, copper, zinc, chromium, and titanium the 7075 alloy also known as Zicral or Fortal Structural has one of the highest strengths and fatigue resistance compared to other aluminum alloys. It is used to manufacture shafts and gears for the automotive industry, bike frames, and aircraft components. It is highly used in extrusion processes and even though it is very strong, it has good machinability. The presence of copper in the alloy decreases its corrosion resistance and it may be coated or anodized to protect it from harsh environments.

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Before a design is completely manufactured and ready to use, surface finishing operations take place. These operations have 2 main functions: enhancing the corrosion resistance of the alloy and giving a better appearance to the product.

Here are some of the most common surface finishing operations performed on aluminum:

1. Mechanical Machining

Tolerances achieved in the manufacturing process are far from desired and a grinding operation is needed. Grinding is a basic mechanical machining operation in which excess material is removed from the product’s surface and it can be performed in a CNC machining mill or lathe depending on the product’s geometry. Abrasive sandblasting is applied to smoothen the surface before painting and to remove oxide. A polishing process gives a smooth mirror-like appearance to aluminum.

2. Anodizing

This operation is done to provide the aluminum with extra corrosion resistant layers making the surface more durable. The anodizing process can also be used to provide electrical insulation and colored finished to the product.

3. Painting

A regular painting operation is performed to protect the material from external agents that may damage its surface. Before painting it is recommended to polish the surface to achieve the best appearance. Painting admits a wide variety of colors and may also provide electrical insulation.

4. Powder coating

Its main goal is to provide the surface with extra corrosion resistance but it also increases impact resistance, UV protection and is used to color the surface, making it more appealing.

To help you improve your designs, here are some engineering tips for aluminum alloys:

1. The 2XXX wrought alloy series uses copper to increase the fatigue resistance of aluminum but it’s very hard to weld and has poor corrosion resistance. Reserve it for applications outside corrosive environments and where removable fastening elements are allowed.

2. Aluminum has a wear resistance, applying an anodizing or painting process can make the surface more durable.

3. Even though aluminum designs can be manufactured in many ways, the costs related to the processes that allow complex contours may be too high. Keep your design simple!

4. The relatively low costs of aluminum and its high strength-to-weight ratio makes it a proper competitor of steel alloys.

5. Aluminum is easy to recycle, making it cost-efficient since most of it can be recovered after the design’s working lifecycle and the energy-costs of recycling it are less than 5% of what its needed to make it from bauxite