• 21 April 2024

The hardness of a metal is a characteristic of how well a material resists local plastic deformation. There are several different scales and systems that measure the hardness of a metal such as aluminum.

Aluminum hardness scale by method

When it comes to determining hardness, the Mohs scale is most commonly used. This system determines hardness based on surface wear - scratching one material with other materials. If material A can scratch material B, then material A is harder than B. This scale is used almost exclusively for minerals and precious stones, but it can also be applied to metals. In this case, the Hardness of aluminum is at 2.75 and is between tin and copper.

The Rockwell hardness method compares two indentations made in a material. One made with a low load, the other with a high load. A unique feature of the Rockwell scale is that it correlates linearly with the tensile strength of the material. Rockwell hardness is usually reserved for harder materials. The hardness of aluminum here is in the range of 20 - 25 points. And, as with Mohs, it is between tin and copper.

The Brinell hardness scale is a widely accepted measure of the hardness of materials. It involves pressing a ball of steel (or tungsten carbide for harder materials) into the test piece with a constant and known force. The softer the material, the deeper the ball will penetrate, and vice versa. The next step is to measure the diameter of the resulting impression. The hardness scale for aluminum using this method is 15 points.

The Vickers hardness scale uses a square pyramid-shaped diamond that is imprinted into the material. A measurement is then taken. The size of the impression determines how deeply it has been pushed into the material. A formula is then used to determine the hardness of the material. Aluminum here records a hardness of 160 - 350 points.

Scale of aluminum hardness according to alloy

Aluminum is most often combined with copper, zinc, magnesium, silicon, manganese and lithium. Small additions of chromium, titanium, zirconium, lead, bismuth and nickel are also added. There are more than 300 wrought alloys, of which 50 are in common use. They are usually identified by a four-digit system that originated in the US and is now widely accepted. A table of aluminum alloys usually ranks them from hardest to least resistant to deformation. However, the aluminum hardness scale does not always reflect the properties of a particular alloy.

Cast vs. forged aluminum

Aluminum alloys can be generally divided into two categories: cast aluminum alloys and wrought aluminum alloys. Cast aluminum alloys are those that contain > 22% alloying elements in their composition. The percentage of alloying elements has a huge impact on the material's properties. Aluminum loses its ductility as more alloying elements are added, making most cast alloys prone to cracking. Conversely, forged alloys have allowed designers to increase aluminum's strength, corrosion resistance, conductivity, etc., While maintaining ductility and other favorable properties.

Cast aluminum alloys typically have low melting points and tensile strengths compared to forged aluminum. The most widely used aluminum alloy is aluminum-silicon alloy, which has a high silicon content, allowing the alloy to be easily cast. The whole and properties of the various alloys are shown in the table of aluminum alloys. The hardest aluminum alloys

The table of aluminum alloys shows that the hardest ones are the 7xxx series alloys. However, they have a major disadvantage - they are prone to stress corrosion cracking. The scale of aluminum hardness here is high due to the elements used. The most common is 1 to 9% zinc, 1 to 3% magnesium, and for some alloys up to 3.0% copper, aluminum. These alloys are strengthened by heat treatment. The applications of these alloys are related to their high strength. These are - aerospace engineering, military equipment and nuclear power equipment. In addition, they are used in construction, as well as in the manufacture of sports equipment, such as ski poles and tennis rackets.

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