Brass Plate Testing

Brass plate inspection mainly conducts scientific testing and analysis on the chemical composition analysis, mechanical property testing, dimension and shape deviation inspection, surface quality inspection, electrical and thermal conductivity testing and corrosion resistance evaluation, objectively assessing the product quality grade and issuing a detailed test report, providing a basis for manufacturers' quality control and downstream users' product acceptance.

Testing Items

Chemical composition analysis: Through the techniques such as the spectrometry analysis, the contents of the copper (Cu), zinc (Zn) and main alloying elements (such as the lead, iron, tin and aluminium) in the brass plate are precisely determined. This is the basis for judging whether the brass designation (such as H62, H68 and HPb59-1) meets the standard, directly affecting the mechanical properties, corrosion resistance and processing characteristics of the material.

Mechanical property testing: Mainly including the determination of the tensile strength, yield strength, elongation after fracture and hardness (Brinell, Rockwell or Vickers). These indicators directly reflect the load-bearing capacity, deformation ability and wear resistance of the brass plate under the loading conditions, and are the key to evaluating whether it meets the use requirements of the structural or wear-resistant parts.

Dimension and shape deviation inspection: The precision measuring tools (such as the micrometers, callipers and tape measures) and optical projectors are used to measure the dimensions and shape parameters such as the thickness, width, length, flatness and camber of the brass plate, ensuring that they meet the tolerance requirements of the drawings or the relevant product standards (such as GB/T 17793). It is the premise for ensuring the subsequent assembly and processing precision.

Surface quality inspection: Under the sufficient lighting, through the visual inspection or with the aid of the low-power magnifying glasses, it is checked whether there are the defects such as the cracks, peeling, inclusions, oxidation colours, scratches, indentations and corrosion on the plate surface. The surface quality not only affects the appearance, but also may become the stress concentration points, reducing the fatigue life and corrosion resistance of the parts.

Electrical and thermal conductivity testing: A conductivity tester or thermal conductivity tester is used to determine the electrical conductivity and thermal conductivity of the brass plate. As an important electrical engineering and heat dissipation material, the electrical and thermal conductivity performances of the brass are one of the core parameters for the material selection, directly affecting the efficiency of the electrical connection parts and the effectiveness of the heat dissipation devices.

Corrosion resistance evaluation: The salt spray testing (such as the neutral salt spray testing NSS) is usually adopted to simulate the harsh environments, evaluating the corrosion resistance of the brass plate. By observing the time and morphology of the corrosion products appearing on the specimen surface, the coating quality or the corrosion resistance grade of the material itself is judged. It is suitable for the environments such as the marine and chemical industries.

Testing Scope

Brass plates of the different designations: The testing scope covers the common brass designations, such as the ordinary brass (H90, H68 and H62), leaded brass (HPb59-1 and HPb63-3) and tin brass (HSn62-1). Due to the composition differences of the different designations, the key items and index limits of the testing have different emphases, and need to be carried out according to the corresponding standards.

Plates of the multiple processing states: Including the hot-rolled plates, cold-rolled plates, and the products of the different heat treatment states such as the annealed (soft state), half-hard state and hard state. The processing states significantly affect the mechanical properties and internal structures of the material. During the testing, the supply state must be clearly defined, and the corresponding testing methods should be adopted.

Plates of the different specifications and thicknesses: From the ultra-thin plates (thickness < 0.1 mm) to the thick plates (thickness > 50 mm), from the narrow-width to wide-width plates. The sample preparation methods, testing equipment and performance evaluation standards of the samples of the different specifications may be different, and the suitable testing schemes need to be selected according to the specific product standards.

Plates after the surface treatments: The testing scope extends to the brass plates after the surface treatments such as the electroplating (such as the nickel plating and chromium plating), chemical polishing, passivation and coating. At this time, the special tests such as the coating thickness, adhesion, porosity and the corrosion resistance after the surface treatments need to be added to the testing items.

Special plates for the specific application fields: Such as the elastic brass strips for the electronic connectors, embossed brass plates for the building decoration and special brass plates for manufacturing the cartridge cases. For these special materials, in addition to the routine items, the special performance tests such as the elastic limit, stress relaxation and the corrosion in the specific media also need to be carried out.

Raw materials and finished plates: The testing runs through the whole process from the melted and cast brass ingots (slabs) to the final rolled finished products. The testing of the raw materials helps to control the source quality, and the testing of the finished products is the basis for the final delivery and acceptance.

Testing Methods

Spectrometry analysis method (OES/ICP): The spark discharge atomic emission spectrometry (OES) or inductively coupled plasma atomic emission spectrometry (ICP-OES) is adopted for the chemical composition analysis. The OES is suitable for the fast non-destructive screening of the bulk samples; the ICP method has the higher precision and can analyse a wider range of elements, especially suitable for the determination of the trace elements.

Tensile testing method: In accordance with the standards such as GB/T 228.1 or ISO 6892-1, the standard tensile specimens are prepared and tested on a universal material testing machine. By recording the load-displacement curves, the tensile strength, yield strength and elongation after fracture are calculated. It is the most classic and direct method for evaluating the mechanical properties of the material.

Hardness testing method: According to the thickness and state of the plate, the Brinell hardness (HBW, suitable for the thicker or softer materials), Rockwell hardness (HRB/HRE, suitable for the thin plates or medium-hardness materials) or Vickers hardness (HV, suitable for the thin layers or precise measurement) testing is selected. During the testing, it is necessary to ensure that the back side is flat without the supporting cavities, and the results are valid only in this way.

Metallographic examination method: The specimens are cut, and after the mounting, grinding, polishing and etching (commonly with the ferric chloride hydrochloric acid solution), the microstructure is observed under a metallographic microscope. The grain size, second-phase distribution, inclusion contents and processing flow lines can be evaluated, used to analyse the reasons for the advantages and disadvantages of the material performance and whether the heat treatment process is appropriate.

Eddy current conductivity testing method: A non-destructive testing method based on the eddy current principle. The probe contacts the brass plate surface, and the conductivity (usually expressed in IACS%) is indirectly determined by measuring the impedance changes caused by the eddy currents. This method is fast and convenient, commonly used for the on-site batch screening and incoming material inspection.

Salt spray testing method: In accordance with GB/T 10125 or ASTM B117, the specimens are placed in an enclosed salt spray test chamber, and the sodium chloride solution of the specified concentration is continuously sprayed, creating a constant-temperature and constant-humidity corrosion environment. After the continuous spraying for a certain period (such as 24 h, 96 h and 240 h), the corrosion conditions on the specimen surfaces are checked and rated.

Testing Standards

Domestic Standards:

1. GB/T 17793, Wrought copper and copper alloys — Plates, sheets and strips

2. GB/T 228.1-2021, Metallic materials — Tensile testing — Part 1: Method of test at room temperature

3. GB/T 229-2020, Metallic materials — Charpy pendulum impact test method

4. GB/T 232-2010, Metallic materials — Bend test method

5. GB/T 230.1-2018, Metallic materials — Rockwell hardness test — Part 1: Test method

6. GB/T 10125-2021, Corrosion tests in artificial atmospheres — Salt spray tests

International Standards:

1. ISO 6892-1, Metallic materials — Tensile testing — Part 1: Method of test at room temperature

2. ISO 9227, Corrosion tests in artificial atmospheres — Salt spray tests

Note: The applicable standard can be selected according to the product use and customer trade requirements; standards agreed in the contract take precedence over general standards.

Testing Instruments and Equipment

Direct-reading optical emission spectrometer: The core equipment for the fast quantitative analysis of the chemical composition. It excites the sample to generate the characteristic spectra, which are received by the CCD detectors after the grating dispersion, and by comparing with the standard sample database, the precise contents of the multiple elements can be simultaneously given within tens of seconds, with the extremely high detection efficiency.

Universal material testing machine: The key equipment for carrying out the mechanical property tests such as the tensile, compression and bending. The modern testing machines are usually composed of the loading frames, servo control systems, high-precision force sensors and extensometers, as well as the computer data acquisition and analysis software, realizing the automatic control of the testing process and the high-precision recording of the data.

Digital hardness tester: Including the various types such as the Brinell, Rockwell and Vickers. The modern hardness testers mostly adopt the electronic loading, and automatically measure the indentations through the optical or sensor methods, directly displaying the hardness values in the digital form, eliminating the human reading errors. Some models are equipped with the software for the data statistics and transmission.

Metallographic microscope system: Composed of the inverted or upright microscope main bodies, digital CCD cameras, image analysis software and automatic stages. It can not only be used for the microstructure observation, but also carry out the quantitative metallographic work such as the grain size rating, phase area percentage calculation and inclusion analysis through the software.

Salt spray test chamber: The dedicated equipment for simulating the marine or industrial atmospheric corrosion environments. The chamber body is made of the corrosion-resistant materials, and is equipped with the precision spraying systems, saturated air barrels, heating and temperature control systems and automatic water replenishing devices, ensuring that the testing conditions (temperature, humidity and salt spray sedimentation rate) are stable, controllable and compliant with the standards.

Precision dimension measuring instruments: Including the digital micrometers (resolution 0.001 mm), large vernier callipers, laser thickness gauges, flat plates and feeler gauges (for measuring the flatness), as well as the coordinate measuring machines (CMM). For the plates of the high precision or complex shapes, the coordinate measuring machines can carry out the precise three-dimensional dimension mapping through the probe contact.