It’s often a difficult task for quality professionals and engineers to ascertain the hardness of a metal such as copper just by sight. Often, the requirements of specifying a metal for a specific design purpose often depend on critical factors that include the hardness of the material. As one of the most used metals in the manufacturing and engineering industry, copper’s material property is often required, and its hardness is a primary identifier of its suitability for many industrial processes. Want to know how to test the hardness of copper? Then read on.
I. What is the Hardness of a Metal?
The ability of a material to maintain its durability relies on its hardness and a very hard metal often lasts longer than a softer material under the same condition. Hence, the hardness of a metal can be described as its ability to resist external forces and loads that can cause its deformation and other external injuries to the metal. These injuries can include wear and tear, abrasion, and surface dents that can affect its efficiency and aesthetics. Determining the hardness of a metal helps designers to calculate its tensile strength which helps to provide a suitable material for a specific design or use case.
II. What is the Hardness of Copper?
The hardness of copper is its ability to resist the application of external forces that might be responsible for damage or inefficiency of the copper material. Copper is naturally soft, and it is used in many industrial products for its anti-corrosion properties and high conductivity especially for electrical conduction purposes. However, to make copper suitable for high intensity impact, specific elements are added to form alloys and increase its hardness. For instance, brass is an alloy containing copper and zinc. Also, bronze contains copper and tin, nickel, aluminum, or beryllium to form the hardest copper alloy.
III. What is the Hardness of Half Hard Copper?
While copper exists at different levels of softness or hardness including cold rolled, high yield, half hard, three quarter hard, and hard, their various hardness value often indicates their specific use. For half hard copper, its hardness value is often designated as H02 according to ASTM B370 as the standard specification. It has a minimum tensile strength of 37Ksi and a maximum of 46Ksi with a yield strength of 30Ksi which makes it useful for instances where malleability and strength are both important.
IV. Is Copper a Hard or Soft Metal?
Copper exists naturally as a soft metal and is limited in its use to manufacturing components that don’t require resisting the impact of an external force or load. Its high thermal and electrical conductivity, and anti-corrosion makes it suitable for different industries including electrical and electronics, chemical, automotive, and building industries. Various components that include cables, tubes, roofing, and refrigeration pipes are some of the products made from copper and some do not need to be hard.
V. Why is Pure Copper Soft?
Many metals including copper are soft in their pure state. The reason is because metals’ internal structure is arranged in a way that the application of an external force causes the metals’ atoms to slide over each other moving in layers. But for pure metals including pure copper the force to move these atoms is really small which explains why they are soft since harder metals need more force to move the atoms.
To make pure metals harder, other elements such as tin, aluminum, nickel, and zinc are added where the atoms of these other elements move in to fill the spaces between the atoms of the pure metals. Hence, it requires more force to move the atoms of the resulting alloy making it harder than its natural soft base metal.
VI. What is the Difference between Soft and Hard Copper?
Soft copper despite being soft in its natural state has unique uses including its uses for manufacturing electrical and electronics components like cables, semiconductors, tubes, and pipes. These components make use of the malleability, high conductivity, and anti-corrosive properties of soft copper. Unlike hard copper which is basically used for its strength and hardness along with its anti-corrosive properties.
VII. How do you Test for Hardness?
Generally, testing the hardness of a material requires the impression from an indenter with a known load for a specified time on the material surface. The depression imprinted on the material after removing the load gives an indication of the material hardness as the measurement of the depth or the width of the impression is used in the formula for calculating the material’s hardness. Further, there are different types of hardness testing methods which measure either the width or the depth of the indentation. For width measurement, the Rockwell hardness test falls in this category, while the Brinell and Vickers hardness test measures the width of the indentation.
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VIII. Test Method for Hardness
Here are the most popular methods of hardness testing.
- Rockwell Test – Using a Rockwell hardness testing machine helps to carry out this test. It also includes a ball indenter made from tungsten carbide in four different sizes that causes a depression when it is released on the surface of the material. A diamond indenter is also used sometimes with loads ranging from 15kgf to 150kgf. The combination of these different indenters and loads gives 30 varieties of Rockwell scales often used in measuring the different hardness values of materials. Also, the sequence of load application involves first a minor load followed by a major load to cause the final depression on the material. The measurement of the depression is used in calculating the Rockwell hardness value.
- Vickers Test – For this test, a wide range of load is employed making it suitable for measuring the hardness of a variety of material thickness and hardness. The indenter in this case is a pyramid-shaped diamond that utilizes loads from 10gf to 100kgf. The specified load is applied to the material surface and the width of the indentation is measured to use in the calculation of the Vickers hardness value of the material. Also, an optical instrument like a microscope helps to measure the indentation.
- Brinell Test – To measure the hardness value of a material with a large surface area or with rough surface, the Brinell hardness test is often ideal for this kind of situation. The reason is because the indentation resulting from the application of the carbide ball indenter with diameters ranging from 1 – 10mm often causes significant indentation. This deep impression makes the Brinell test only suitable for thick materials. Additionally, it uses a load range of 1 – 3,000kgf with an optical instrument for measuring the depression.
Conclusion
In conclusion, though copper is very soft in its natural state, its unique properties which include high conductivity and corrosion resistance make it very useful for many specific uses. However, it can be hardened by adding a variety of elements depending on the intended design or usage. Also, the confirmation of the hardness of copper is often done using one of the three most popular hardness testing methods. These methods include Rockwell, Brinell, and Vickers hardness testing. Your choice of hardness test will be dependent on the material application, size, and accuracy required.