Aluminum Ingot Testing

Aluminium ingot inspection mainly conducts scientific testing and analysis on the chemical composition analysis, hydrogen content determination, inclusion analysis, low-power structure inspection, high-power metallographic analysis and surface quality inspection, 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: The quantitative determination is carried out on the main elements (such as the aluminium content) and impurity elements (such as the silicon, iron, copper, manganese, magnesium, zinc, titanium and chromium) in the aluminium ingots. This is the core of the aluminium ingot testing, directly determining the designations, properties and application fields of the aluminium ingots. Usually carried out according to the GB/T 20975 series or ISO 209 series standards.

Hydrogen content determination: The content of the dissolved hydrogen in the aluminium melt is detected. The hydrogen is the main harmful gas in the aluminium and aluminium alloys, easily forming the blowholes and pinholes during the solidification processes, significantly reducing the compactness and mechanical properties of the material, especially having the significant effects on the subsequent casting or rolling processes.

Inclusion analysis: The contents, sizes and distributions of the non-metallic inclusions (such as the oxides, chlorides and carbides) in the aluminium ingots are detected. The inclusions will destroy the continuity of the metal matrix, becoming the stress concentration points and crack sources, seriously affecting the fatigue strengths, plasticity and corrosion resistance of the material.

Low-power structure inspection: Through the macro etching (such as the tower-shaped specimens), the cross-sections or longitudinal sections of the aluminium ingots are observed, checking whether the macro defects such as the porosity, blowholes, segregation, cracks and slag inclusions exist, as well as the grain sizes and uniformity. It is the important means of evaluating the internal qualities of the cast ingots.

High-power metallographic analysis: The metallographic microscopes or scanning electron microscopes are used to observe the micro-structures of the aluminium ingots, including the grain morphologies, second phase distributions and eutectic silicon morphologies (for the aluminium alloys). This analysis can deeply reveal the micro-structure characteristics of the material and establish the relationships with the mechanical properties.

Surface quality inspection: The visual or instrument-assisted inspection is carried out on the aluminium ingot surfaces, evaluating whether the defects such as the cold shuts, cracks, shrinkage cavities, slag inclusions, fins, burrs and severe oxidation colour differences exist. These defects will affect the subsequent processing and use.

Dimension and shape tolerance measurement: The measuring tools such as the callipers and micrometers are used to measure the geometric dimensions of the aluminium ingots such as the lengths, widths, heights, bending and warpage, ensuring that they meet the requirements of the purchase and sales contracts or the relevant product standards (such as GB/T 1196).

Testing Scope

Aluminium ingots for remelting: Referring to the primary aluminium products used for the re-melting and casting of the cast aluminium alloys or wrought aluminium alloys, such as the designations Al99.90, Al99.85 and Al99.70 conforming to GB/T 1196. The testing emphases are the strict control of the main component aluminium purity and the upper limits of the impurity elements.

Cast aluminium alloy ingots: Referring to the alloy aluminium ingots that have been formulated according to the specific compositions and can be directly used for casting the parts, such as ADC12 and A356. The testing needs to cover the precise control of the alloying elements (silicon, copper and magnesium, etc.), as well as the gas and inclusion contents.

Wrought aluminium alloy ingots: Referring to the alloy ingots used for the subsequent plastic processing such as the rolling, extrusion and forging into the plates, profiles and pipes. The testing particularly pays attention to the composition uniformity, low-power structure compactness, as well as the impurity elements affecting the hot working properties.

High-purity aluminium ingots: Referring to the aluminium products with the aluminium contents higher than 99.99% (4N) and above. The testing has the extremely high precision requirements. The high-sensitivity instruments such as the glow discharge mass spectrometry (GD-MS) need to be adopted for the ppb-level analysis of the trace impurities (such as the sodium, calcium, iron and silicon).

Electrical aluminium ingots: The aluminium ingots specially used to produce the conductive materials such as the wires and cables. In addition to the routine compositions, the contents of the elements affecting the electrical conductivities such as the iron, silicon, vanadium and titanium need to be emphatically detected, and the total impurities need to be strictly controlled.

Recycled aluminium ingots: The aluminium ingots made by the recovery and remelting of the aluminium scrap. The testing scope needs to extend to the possible trace "residual elements" (such as the lead, chromium, nickel and tin), evaluating whether they meet the limit requirements of the specific alloys or application fields.

Imported/exported aluminium ingots: For the aluminium ingots involving the international trade, the testing needs to simultaneously meet the Chinese standards (GB), international standards (ISO) or the standards of the destination countries/regions (such as ASTM, JIS and EN), and issue the credible testing reports for the customs clearance and settlement.

Testing Methods

Spark discharge atomic emission spectrometry (OES): Currently the most mainstream method of the aluminium ingot chemical composition analysis. The characteristic spectra are generated through the arc excitation of the samples for the quantitative analysis, with the advantages of the fast analysis speeds (tens of seconds), high precision and simultaneous determination of the multiple elements, suitable for the fast analysis before the furnaces and finished product inspection.

Inductively coupled plasma atomic emission spectrometry (ICP-OES): After the samples are dissolved, the high-temperature plasma is used for the excitation, and the characteristic spectral line intensities are measured for the quantification. With the low detection limits, wide linear ranges and strong anti-interference abilities, especially suitable for the precise determination of the trace impurity elements in the high-purity aluminium.

Inert gas fusion-infrared absorption/thermal conductivity method: Used to determine the hydrogen, oxygen and nitrogen gas contents in the aluminium ingots. The samples are melted at the high temperatures in the graphite crucibles, and the released gases are carried by the inert carrier gases into the infrared detection cells (for the hydrogen and oxygen measurement) or thermal conductivity detection cells (for the nitrogen measurement) for the analysis. The results are accurate and reliable.

X-ray fluorescence spectrometry (XRF): The X-rays are used to irradiate the samples, measuring the excited characteristic X-ray fluorescence for the element analysis. This method has the simple sample preparation, non-destructive and fast characteristics, often used for the fast screening and semi-quantitative analysis of the aluminium ingot compositions, or for the online testing.

Metallographic microscopic analysis method: Through a series of sample preparation steps such as the sampling, mounting, grinding, polishing and etching, the observable specimens are prepared, and their micro-structures are observed under the optical microscopes or electron microscopes, evaluating the grain sizes, phase compositions and defects.

Macro etching (low-power) inspection method: The aluminium ingot specimens are immersed in the specific etchants (such as the hydrochloric acid or mixed acid solutions) for a certain time. After the cleaning, the macro structures and defects on their cross-sections are observed with the naked eyes or with the help of the magnifying glasses. The method is intuitive and simple to operate.

Ultrasonic flaw detection method: Using the principle that the ultrasonic waves generate the reflections or attenuation when encountering the defects (such as the shrinkage cavities and cracks) during the propagation inside the aluminium ingots, the signals are received and imaged through the probes, thereby realizing the non-destructive testing and defect positioning of the aluminium ingot interiors.

Testing Standards

Domestic Standards:

1. GB/T 1196, Unalloyed aluminium ingots for remelting

2. GB/T 20975, Methods for chemical analysis of aluminium and aluminium alloys

International Standards:

1. ISO 209, Wrought aluminium and aluminium alloys — Chemical composition

2. EN 576, Aluminium and aluminium alloys — Unalloyed aluminium ingots for remelting — Classification and composition

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

Spark direct-reading spectrometer: The core equipment of the aluminium ingot testing laboratories, equipped with the dedicated aluminium matrix standard samples and argon purification systems, ensuring the analysis stability and accuracy. Usually integrating the vacuum or argon-filled optical systems, high-resolution CCD detectors and professional analysis software.

Inductively coupled plasma optical emission spectrometer (ICP-OES): Composed of the radio frequency generators, plasma torch tubes, nebulization systems, dispersion systems and detection systems. It needs to be equipped with the hydrofluoric acid-resistant sampling systems (such as the platinum center tubes and PFA nebulizers) to process the acid-dissolved aluminium samples.

Oxygen-nitrogen-hydrogen analyser: The equipment specially used to determine the gas contents in the metals. The key components include the high-frequency induction heating furnaces or pulse electrode furnaces, high-precision infrared detection cells, thermal conductivity detection cells, as well as the high-purity carrier gas (helium or argon) purification systems, requiring the low and stable blank values.

Metallographic microscope and image analysis system: Including the inverted or upright optical microscopes, automatic stages, high-resolution cameras and professional image analysis software. Can be used for the grain size rating, phase area fraction measurement and inclusion statistical analysis, etc.

Scanning electron microscope and energy dispersive spectrometer (SEM-EDS): Used for the ultra-high-magnification morphology observation and micro-area composition qualitative and semi-quantitative analysis of the inclusions and second phase particles in the aluminium ingots, and is the powerful tool of deeply studying the micro-structures and defect causes of the material.

Ultrasonic flaw detector: Divided into the portable and fixed types. For the aluminium ingot testing, the multi-channel automatic flaw detection systems are mostly adopted, combined with the immersion method or water-spray coupling methods, realizing the automatic scanning, imaging and judgment of the internal defects of the aluminium ingots.

Precision dimension measurement tools: Including the digital vernier callipers, outer diameter micrometers, height gauges, platforms and squares, etc. Used to precisely measure the geometric dimensions and geometric tolerances of the aluminium ingots, ensuring that they meet the product specification requirements.