Invented in 1900 in Sweden, the Brinell test is one of the oldest hardness tests still in use today. In this test, a load is applied to a hardened sphere (constructed to a specific diameter) over a work piece. The load causes the sphere to indent the work piece placed beneath the sphere. A material's Brinell hardness value is assigned based on the size of the indentation made on the work piece and the weight of the load needed to make the indentation. The Brinell number is defined as the weight of the applied load in kilograms divided by the indentation in square millimeters. Aluminum measures approximately 115 on the Brinell scale, which ranges from 0 to 10,000.
The Rockwell test of hardness is conducted in much the same fashion as the Brinell test. Pressure is applied to a work piece on either a steel or diamond-tipped spherical indenter. Indenters and the size of the load used for measurements are assigned a letter (A or B, for example). Different work pieces are measured on different scales. Aluminum is measured using the B scale, which ranges from 0 to 110. Aluminum's hardness is approximately 68B on the Rockwell scale.
Aluminum has many desirable properties, which is why its use is so widespread. Aluminum has a relatively low density (0.098 pounds per cubic inch) among metals. Aluminum is very ductile and resistant to corrosion. Heat-treating aluminum or adding other elements like silicon and manganese greatly increases aluminum's strength and durability. Aluminum melts at approximately 1,220.7 degrees Fahrenheit.
Aluminum's low density lends to its widespread use in the many industries such as the aerospace industry. Cookware and pressure vessels are often constructed out of aluminum, as are countless cans and bottles. Aluminum is also widely used in transportation, electrical transmission and construction.