Aluminum Alloy Material Testing

Aluminium alloy material inspection mainly conducts scientific testing and analysis on the chemical composition analysis, mechanical property testing, metallographic structure analysis, dimension and geometric tolerance testing, surface quality and coating testing and physical property testing, 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: This is the basis of the aluminium alloy material inspection, aiming to precisely determine the contents of the aluminium (Al) and alloying elements (such as Si, Cu, Mg, Mn and Zn), as well as the limits of the impurity elements (Fe, Pb and Sn, etc.). Through the chemical methods and spectroscopic methods, whether the material meets the standard designation requirements such as GB/T 3190 and ASTM B209 is verified, ensuring that the basic properties of the material match the design expectations.

Mechanical property testing: Used to evaluate the behavior characteristics of the aluminium alloy under the applied forces, and is the key to judging whether it is suitable for the load-bearing structures. The main testing items include the tensile strength, yield strength, elongation after fracture, reduction of area and hardness (Brinell, Vickers and Rockwell). These data are directly related to the safety, reliability and service lives of the material.

Metallographic structure analysis: The micro-structures of the aluminium alloy, including the grain sizes and morphologies, the distributions, amounts and morphologies of the second phases (such as the strengthening phases and impurity phases), are observed through the optical microscopes or scanning electron microscopes. This analysis can reveal the metallurgical quality and heat treatment states (such as whether the solution treatment and aging are sufficient) of the material, and can assist in the diagnosis of the material defect causes.

Dimension and geometric tolerance testing: The actual dimensions (such as the thicknesses, widths and diameters) and geometric tolerances (such as the straightness, flatness and roundness) of the aluminium alloy plates, sections, castings or forgings are measured. This testing ensures that the product geometric precision meets the drawing and technical agreement requirements, and is the premise of guaranteeing the subsequent assembly and use functions.

Surface quality and coating testing: Whether the aluminium alloy material surfaces have the defects such as the cracks, peeling, bubbles, inclusions and corrosion spots is checked. For the products with the surface treatments such as the anodizing, electrophoretic coating and powder spraying, the coating thicknesses, adhesion, hardness, corrosion resistance (such as the salt spray testing) and colour differences also need to be tested, to evaluate their decorative and protective properties.

Physical property testing: Covering the determination of the parameters such as the density, electrical conductivity, thermal conductivity and thermal expansion coefficient. These properties are crucial for the application of the aluminium alloy in the specific fields such as the electronics, heat dissipation and aerospace, and directly affect the thermal management efficiency, electromagnetic compatibility and dimension stability of the products.

Testing Scope

Wrought aluminium alloys: Mainly including the plates, strips, foils, pipes, bars, sections and wires made through the plastic processing methods such as the rolling, extrusion and forging. The testing needs to be carried out targeted on the mechanical, dimension and surface quality items according to their processing states (such as the O, H and T states) and product forms, involving the standards such as GB/T 3880 and GB/T 6892.

Cast aluminium alloys: Referring to the aluminium alloy castings produced through the processes such as the sand casting, permanent mold casting and die casting. The testing emphases are the chemical composition uniformity, non-destructive flaw detection of the internal defects (such as the porosity, blowholes and shrinkage cavities), mechanical properties (especially the tensile strength and elongation) and dimension precision, and the relevant standards include GB/T 1173 and GB/T 15114.

Aluminium alloy weldments: Targeting the aluminium alloy components connected through the welding processes such as the MIG and TIG. The testing core is the weld quality, including the chemical compositions of the welds and heat-affected zones, mechanical properties (tensile and bending), metallographic structures, internal defects (X-ray and ultrasonic flaw detection) and surface forming, to ensure the integrity and reliability of the welded joints.

Aluminium alloy composite materials: Such as the aluminium-based silicon carbide particle reinforced composites and aluminium-steel clad plates. In addition to the base alloy properties, the testing focuses more on the distributions and contents of the reinforcement phases, interface bonding strengths, anisotropic properties, as well as the evaluation of the specific functional properties (such as the wear resistance and specific strengths).

Recycled aluminium alloys: The aluminium alloys made by the recovery and remelting of the aluminium scrap. The testing needs to particularly pay attention to the accumulation control of the impurity elements (such as Fe, Mn and Cr), metallurgical qualities (inclusions and hydrogen contents), as well as the property stability of the final products, to ensure that they meet the quality requirements of the specific application fields.

Special functional aluminium alloys: Including the high-strength high-toughness aluminium alloys, corrosion-resistant aluminium alloys, heat-resistant aluminium alloys and special anodizing aluminium alloys. In addition to the routine items, the testing scope needs to go deep into their special properties, such as the stress corrosion susceptibility, high-temperature lasting strengths and anodizing film characteristics, verifying their functional specificity.

Testing Methods

Spectroscopic analysis method (OES/ICP): The spark discharge atomic emission spectrometry (OES) is the mainstream method of the fast quantitative analysis of the aluminium alloy chemical compositions on site, with the high precision and fast speed. The inductively coupled plasma atomic emission spectrometry (ICP-OES) is often used for the trace element analysis and arbitration inspection, with the wider linear ranges and lower detection limits.

Tensile testing method: According to the standards such as GB/T 228.1 or ASTM E8, the axial tensile loads are applied to the standard specimens on the universal material testing machines until the fracture, and the key mechanical parameters such as the tensile strength, yield strength and elongation after fracture are automatically recorded and calculated. This is the most direct method of evaluating the load-bearing and deformation abilities of the material.

Hardness testing method: According to the material states and expected hardness ranges, the Brinell hardness (HBW, suitable for the softer or medium-hardness materials), Vickers hardness (HV, suitable for the thin materials or surface treatment layers) or Rockwell hardness (HRB/HRE, suitable for the medium-hardness materials) is selected for the testing. This method is simple to operate and causes the small damage to the specimens.

Metallographic microscopic analysis method: Through the sample preparation processes such as the sampling, mounting, grinding and polishing and etching, the metallographic specimens are prepared, and their micro-structures are observed with the optical microscopes or scanning electron microscopes. The grain sizes and second phase area fractions, etc. can be quantitatively analysed, and it is the important means of studying the process-structure-property relationships of the material.

Non-destructive testing method: Under the premise of not destroying the material, the internal and surface defects are probed. The common methods include: ultrasonic flaw detection (UT, detecting the internal cracks and inclusions), radiographic flaw detection (RT, detecting the volumetric defects), eddy current flaw detection (ET, detecting the surface and near-surface cracks and electrical conductivity changes) and penetrant flaw detection (PT, detecting the surface open defects).

Corrosion property testing method: Evaluates the environmental corrosion resistance of the aluminium alloy. The neutral salt spray testing (NSS, according to GB/T 10125) is the common method of accelerating the evaluation of the coating or matrix corrosion resistance. In addition, the more professional evaluation means such as the intergranular corrosion testing, exfoliation corrosion testing and electrochemical testing (such as the polarization curve measurement) are also included.

Testing Standards

Domestic Standards:

1. GB/T 3190, Wrought aluminium and aluminium alloy — Chemical composition

2. GB/T 3880, Wrought aluminium and aluminium alloy plates, sheets and strips for general engineering

3. GB/T 6892, Wrought aluminium and aluminium alloys — Extruded profiles for general engineering

4. GB/T 1173, Casting aluminium alloys

5. GB/T 15114, Aluminium alloy die castings

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

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

8. GB/T 4340.1-2009, Metallic materials — Vickers hardness test — Part 1: Test method

9. 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

3. ASTM E8, Standard test methods for tension testing of metallic materials

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 spectrometer: Used for the fast quantitative analysis of the aluminium alloy chemical compositions. The instrument excites the samples to generate the characteristic spectra, which are received by the CCD detectors after the grating dispersion, and compared with the built-in standard curves, the contents of the various elements can be simultaneously given within tens of seconds. It is the core equipment of the smelting and incoming material inspection links.

Universal material testing machine: The key equipment of carrying out the mechanical property testing such as the tensile, compression and bending. The modern models are equipped with the high-precision transducers, digital controllers and computer data acquisition systems, which can precisely control the loading rates, display and record the load-displacement curves in real time, and automatically calculate the various mechanical property indicators.

Hardness tester: According to the different principles, divided into the Brinell, Rockwell, Vickers and micro Vickers types, etc. The equipment presses the indenters of the specific shapes and sizes into the specimen surfaces under the standard test forces, and measures the indentation sizes or depths, thereby converting and obtaining the hardness values. The digital hardness testers can directly read and store the data.

Metallographic microscope and image analysis system: The metallographic microscopes are used to observe the micro-structures of the aluminium alloy. The digital microscopes equipped with the cameras can transmit the images to the computers, and combined with the professional image analysis software, the automatic or semi-automatic quantitative analysis of the grain sizes, phase proportions and defect areas can be carried out, improving the analysis precision and efficiency.

Scanning electron microscope and energy dispersive spectrometer: The SEM provides the micro morphology images with the higher resolutions and larger depths of field than the optical microscopes. The equipped X-ray energy dispersive spectrometers (EDS) can carry out the qualitative and semi-quantitative chemical composition analysis of the micro-areas while observing the morphologies, and are the powerful tools of studying the alloy phase compositions, fracture morphologies and failure analysis.

Non-destructive testing equipment: Including the ultrasonic flaw detectors (A-scan, B-scan and phased array), X-ray real-time imaging systems, eddy current flaw detectors and penetrant testing reagent kits. These equipment are based on the different physical principles and are specially used to detect the discontinuity defects inside or on the surfaces of the material, and are the important technical means of guaranteeing the safety of the key components.

Salt spray test chamber: The accelerated corrosion testing equipment used to simulate the marine or salt-containing humid atmospheric environments. Through the atomization of the sodium chloride solution of a certain concentration, the uniform salt spray environments are formed in the closed chambers, and the corrosion resistance of the specimens within the specified times is tested. It is the standard equipment of evaluating the aluminium alloy surface treatment qualities and material corrosion resistance.