Non-Ferrous Metals

Examination of Copper and Copper Alloys

Non-ferrous metals, particularly copper and its alloys, play a critical role in various applications. The most well-known copper alloy as a material is brass. Brass consists of two elements—copper and zinc—with a zinc content typically greater than 15%. Brass is a well-formable material with countless uses, offering high corrosion resistance, long durability, and wear resistance. To further improve its material properties, additives are incorporated, resulting in over 60 different types of brass. The microstructure formation and associated material properties are closely tied to heat treatment.

Testing of Water-Conveying Components

Brass is often used as a material in sanitary applications, such as faucets, supply pipes, connection pipes, fittings, and distributors. Many of these components involve water-conveying parts, meaning they come into contact with tap water. Tap water can be hard or soft, hot or cold, and, due to its mineral content, acts as an electrolyte. Every brass component, regardless of installation location or water quality, must withstand these demands. Furthermore, mechanical stresses such as torque or tension caused by installation can also affect the components. It is essential to ensure that corrosion or cracks do not lead to leaks, especially in water-conveying components. We offer two tests specifically designed to assess these risks:

Dezincification Resistance

Resistance to Stress Corrosion Cracking

Dezincification Resistance

Brass consists of copper and zinc, forming different phases during heat treatment. The α-phase, characterized by light needle-like crystals, offers high corrosion resistance. The β-phase, which is richer in zinc and consists of darker crystals, is less resistant to corrosion. There are also mixed α and β phases as well as other microstructural components due to alloying additions.
Dezincification occurs when zinc is leached out from the surface of the brass, leading to spongy copper structures that can result in material fatigue.

In our laboratory, we prepare a sample from the component using a metallographic cross-section and store it at +75°C in a copper(II) chloride solution. This solution accelerates the leaching of zinc from the brass structure. After the storage period, we section the prepared sample and grind down to the storage plane to evaluate the depth of dezincification under the microscope.

Resistance to Stress Corrosion Cracking

Stress corrosion cracking occurs when internal and external tensile stresses combine with the presence of corrosive media. This results in crack formation without significant deformation, with intergranular or transgranular crack progression. This cracking can appear after a short period, even if the surface shows no visible signs of corrosion. Alloys with lower copper content are more susceptible to stress corrosion cracking. Suitable heat treatment can alleviate internal material stresses, which are often the cause of cracking. If heat treatment after cold forming is not feasible, this must be considered during material selection.

In our lab, we simulate the installation conditions of the test parts. We often use ammonia and its compounds as the corrosive medium. After sample preparation, the test specimens are stored in the gas phase of the selected medium and regularly assessed. After the specified testing period, the test pieces are examined and evaluated under a microscope. This allows us to detect even the smallest cracks, which are invisible to the naked eye but can cause significant damage once installed.

Spannungsrisskorrosion