Aluminum Rod Testing

Aluminium bar inspection mainly conducts scientific testing and analysis on the chemical composition analysis, mechanical property testing, dimension and geometric tolerance testing, surface quality inspection, internal defect non-destructive testing and micro-structure 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: Through the spectroscopic or wet analysis, the main content of the aluminium (Al) in the aluminium bars, as well as the contents of the alloying elements and impurity elements such as the silicon (Si), iron (Fe), copper (Cu), manganese (Mn), magnesium (Mg), zinc (Zn) and titanium (Ti) are precisely determined. This is the basic basis of judging whether the aluminium alloy designations (such as 6061 and 7075) are consistent and whether the material properties meet the expectations.

Mechanical property testing: Mainly evaluating the behavior characteristics of the aluminium bars under the stressed states. The key indicators include the tensile strength, yield strength, elongation after fracture and hardness (Brinell, Rockwell or Webster hardness). These data are directly related to the safety and reliability of the aluminium bars in the final products (such as the structural parts and load-bearing components).

Dimension and geometric tolerance testing: The tools such as the callipers, micrometers and coordinate measuring machines are used to precisely measure the diameters, lengths, out-of-roundness and straightness (bending) of the aluminium bars. The strict dimension control is the premise of guaranteeing their interchangeability and fit precision in the subsequent machining or direct assembly.

Surface quality inspection: Through the visual inspection or with the help of the magnifying devices, whether the aluminium bar surfaces have the defects such as the cracks, peeling, bubbles, scratches, corrosion spots and inclusions is checked. The surface qualities not only affect the appearance, but may also become the stress concentration points, causing the fatigue fractures.

Internal defect non-destructive testing: The ultrasonic flaw detection (UT) technology is adopted. Using the reflection and attenuation characteristics of the high-frequency sound waves inside the material, whether the defects such as the shrinkage cavities, porosity, inclusions and cracks exist inside the aluminium bars is non-destructively detected, evaluating their internal integrity.

Micro-structure (metallographic) analysis: The aluminium bar samples are cut, and after the grinding, polishing and etching, the grain sizes, morphologies, second phase distributions and whether the overburned structures exist are observed under the metallographic microscopes. The micro-structures are the fundamental factors determining the mechanical properties and process properties of the material.

Electrical conductivity/resistivity testing: For the aluminium bars used as the conductive materials (such as the electrical round aluminium rods), the conductivity testers or micro-ohmmeters need to be used to measure their electrical conductivities (%IACS) or resistivities. This is the key indicator of evaluating their conductive properties and ensuring the power transmission efficiencies.

Testing Scope

Alloy designation coverage: The testing scope covers the various wrought aluminium alloy bars of the 1xxx to 7xxx series, such as the pure aluminium series (1060 and 1100), aluminium-magnesium-silicon series (6061 and 6063), aluminium-zinc-magnesium-copper series (7075 and 7050) and aluminium-copper series (2024), etc. The testing emphases need to be determined according to the standard requirements of the different designations.

Product specification coverage: Suitable for the aluminium bar products of all the common cross-section shapes such as the extruded round bars, cast round bars, square bars and hexagonal bars of the different diameters (from several millimetres to hundreds of millimetres) and lengths (fixed lengths or multiple lengths).

Production process coverage: The testing runs through the whole processes of the aluminium bar production, including the incoming re-inspection of the ingots (billets) after the melting and casting, process inspection of the semi-finished products after the extrusion or forging, as well as the comprehensive ex-factory inspection of the final finished products.

Application field coverage: The testing depths are determined according to the final uses of the aluminium bars. For example, the high-strength aluminium bars for the aerospace need the comprehensive mechanical property and non-destructive testing; the aluminium bars for the building curtain walls focus on the dimension precision and surface qualities; the aluminium bars for the automotive lightweight structural parts need to take into account the strengths, toughness and fatigue properties.

Defect type coverage: The testing needs to identify and evaluate the various defects, including the surface defects (cracks, scratches and oxidation), near-surface defects (subcutaneous bubbles and inclusions), internal defects (cavities and segregation), as well as the structure defects (coarse grains and overheated/overburned structures).

Standard conformity coverage: The testing activities need to ensure that the products meet all the specified requirements in the relevant national standards (GB/T), industry standards (YS/T), international standards (ISO and ASTM) or specific customer technical agreements.

Testing Methods

Spectroscopic analysis method (OES): The direct-reading spectrometers are used. The aluminium bar sample surfaces are ground flat and used as the electrodes. Under the arc or spark excitation, the quantitative analysis is carried out according to the intensities of the characteristic spectral lines. This method is fast and accurate, and is the standard method of the chemical composition fast screening and control on the production sites.

Tensile testing method: According to the GB/T 228.1 or ASTM E8 standards, the samples are taken from the aluminium bars and machined into the standard tensile specimens. On the universal material testing machines, the loading is carried out at the constant rates until the fracture, automatically recording the load-displacement curves, thereby calculating the tensile strengths, yield strengths and elongations after fracture.

Ultrasonic flaw detection method (UT): The pulse-echo ultrasonic flaw detectors are adopted. The probes are coupled with the aluminium bar surfaces, transmitting the ultrasonic beams. Through the analysis of the positions, amplitudes and waveforms of the reflected echoes of the internal defects, the depths, sizes and natures of the defects are judged. The common methods include the longitudinal wave vertical flaw detection and shear wave oblique incidence flaw detection.

Metallographic inspection method: According to the standards such as GB/T 3246 or ASTM E3, the representative cross-section or longitudinal-section specimens are cut from the aluminium bars. After the mounting, rough grinding, fine grinding, polishing and chemical or electrolytic etching, the observation, photographing and rating are carried out under the metallographic microscopes, analysing their micro-structure states.

Dimension measurement method: The simple dimensions such as the diameters use the outer diameter micrometers or callipers with the precision of 0.01mm for the multi-point measurement; for the geometric tolerances such as the straightness, the aluminium bars can be placed on the platforms and the maximum clearances can be measured with the feeler gauges, or the laser scanners can be used for the non-contact high-precision full-size scanning.

Brinell hardness testing method: According to GB/T 231.1, the cemented carbide ball indenters of a certain diameter are used to press into the smooth surfaces of the aluminium bars under the specified test forces. After maintaining for a certain time, the test forces are removed, the indentation diameters are measured, and the Brinell hardness values (HBW) are obtained by looking up the tables or calculating. This method has the large indentation areas and good result representativeness.

Eddy current conductivity testing method: Using the eddy current principle, the probes generate the alternating magnetic fields to induce the eddy currents on the aluminium bar surfaces. The reverse magnetic fields generated by the eddy currents affect the probe impedances. Through the calibration, the impedance changes are converted into the conductivity values (%IACS). This method is fast and non-contact, suitable for the online or on-site testing.

Testing Standards

Domestic Standards:

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

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

3. GB/T 3246, Method for inspection of structure of wrought aluminium and aluminium alloy products

4. GB/T 231.1-2018, Metallic materials — Brinell hardness test — Part 1: Test method

International Standards:

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

2. ISO 6506-1, Metallic materials — Brinell hardness test — Part 1: Test method

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

4. ASTM E3, Standard guide for preparation of metallographic specimens

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: The core equipment of the fast quantitative analysis of the chemical compositions. The modern spectrometers are usually equipped with the argon-purged spark stands, high-resolution dispersion systems and high-sensitivity CCD detectors, which can simultaneously analyse more than ten elements, with the analysis time of only tens of seconds and the high precision.

Universal material testing machine: The key equipment of carrying out the mechanical property testing such as the tensile, compression and bending. Composed of the loading frames, servo control systems, high-precision force transducers and extensometers, equipped with the professional software, it can automatically control the testing processes, collect the data and generate the reports.

Ultrasonic flaw detector: Used for the non-destructive testing of the internal defects. The digital ultrasonic flaw detectors have the high-brightness displays, adjustable gains and gates, and data storage and playback functions. Equipped with the straight-beam probes, angle-beam probes and couplants of the different frequencies and types, to adapt to the aluminium bars of the different specifications and testing requirements.

Metallographic microscope and sample preparation equipment: The system includes the sampling cutting machines, mounting machines, automatic or manual grinding and polishing machines, etching devices, as well as the upright or inverted metallographic microscopes. The microscopes are usually equipped with the bright field, dark field, polarized light observation functions and digital image acquisition systems, used for the structure analysis and rating.

Precision dimension measurement tools: Including the digital outer diameter micrometers (0-1000mm range), large vernier callipers, wall thickness micrometers and radius gauges, etc. For the high-precision or complex profile measurements, the coordinate measuring machines (CMM) need to be used, which can obtain the three-dimensional spatial coordinate point data through the probe contact measurement.

Hardness tester: According to the different standards and requirements, the Brinell hardness testers (such as the HB-3000 type), Rockwell hardness testers (the HRB scales are commonly used) or portable Webster hardness testers need to be equipped. The Brinell and Rockwell hardness testers are bench-type with the high precision; the Webster hardness testers are light and portable, suitable for the on-site fast screening.

Conductivity tester: Usually the portable eddy current conductivity instruments. The readings can be obtained by directly contacting the probes with the measured aluminium bar surfaces. The equipment has the built-in various alloy and temperature compensation curves, wide measurement ranges and simple operations, and is the common tool of the incoming material inspection of the aluminium rods in the industries such as the wires and cables.