Test & measurement
advanced imaging techniques is necessary to ensure these processes do not jeopardise safety and quality.
ALUMINIUM LIGHTWEIGHTING To reduce weight in aircraft, aluminium- lithium (Al-Li) stiffened panels are commonly used in wings, fuselage, empennage and engine casings. To avoid hot cracking in high- strength Al-Li and Aluminium-Zinc-Magnesium (Al-Zn-Mg) alloys, friction stir welding (FSW) is a preferable joining technique. FSW creates a weld by stirring solid metal between adjoining plates rather than melting it, resulting in a lower processing temperature that prevents safety issues caused by cracks or porosity. Unfortunately, the weld region of the alloys often ends up much softer and with reduced yield strength than the base metal. To understand the nanoscale changes occurring within the stirred zone requires further analysis with a combination of advanced imaging technologies In this case, scanning electron microscopy (SEM) can be used to investigate the main elements and composition of intermetallic particles in the base, heat affected zone (HAZ) and weld of these alloys. However, a change in the particles is not easily linked with the decrease in strength present in the weld. Electron backscattered diffraction mapping (EBSD) allows for a deeper dive into the microscopic structure, showing the difference in grain size in the base, HAZ and weld. Although grain refinement in the weld may contribute to improved strength, the possible loss of dislocations could have the opposite effect. Further study utilising a plasma focused ion beam (PFIB) microscope and a transmission electron microscope (TEM) helps to reveal the density of edge and screw dislocations from base to HAZ to weld.
Finally, chemical mapping by Instrumentation Monthly February 2025
energy-dispersive X-ray spectroscopy (EDS) and particle quantification by Automated Particle Workflow (APW) help to reveal the precipitates responsible for increased strength, with this being affected during the welding process.
HOW ALLOYING ELEMENTS IMPACTS QUALITY
Understanding the effect of alloying elements is also crucial for aerospace component quality assurance. For example, in the case of AA2024, a lightweight, corrosion-resistant alloy, adding alloying elements such as copper, magnesium or manganese leads to the formation of precipitates whose type varies based on the applied treatments. Therefore, it is crucial to comprehensively characterise raw materials during the manufacturing process, revealing the compositional and microstructural changes during processes such as aging, hardening or annealing. Using asolution such as the Thermo Scientific Apreo ChemiSEM, it is possible to combine four methods within one microscope — scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) and electron backscatter diffraction (EBSD). The combination of these techniques reveals detailed alloy composition and structure essential for quality control. SEM and EDS provide a microscale characterisation with the Thermo Scientific™ ChemiSEM™ Technology, revealing the compositional data and showing the morphology and elemental makeup of intermetallic particles, particularly phases rich in copper, manganese and magnesium. EBSD maps crystallographic phase, grain structure, grain orientation and morphology, enabling correlations between alloy treatment, grain size and mechanical properties. Such details can be used to optimise heat treatment parameters in orderto achieve desired mechanical properties and performance. The
Apreo ChemiSEM system integrates these analyses, delivering comprehensive insights into precipitates and phases formed through varied aging treatments. This combined approach is invaluable in refining aluminium alloys to meet stringent aerospace standards.
EXTREME TEMPERATURES
Nickel-based superalloys used within aeroplane engines must withstand extreme temperatures up to 2,000°C. The Apreo ChemiSEM’s seamless integration of imaging, EDS and particle analysis offers a comprehensive approach to characterising and optimising these materials for quality assurance.
The high-resolution SEM provides a clear visual overview of the material’s surface and internal structures, while the EDS maps the distribution of elements such as nickel, chromium and aluminium and identifies critical phase compositions. Particle analysis in the ChemiSEM uses automated software to quantify and categorise particles, such as carbides and oxides, within an alloy. This capability allows for the measurement of particle size, shape and distribution — key factors affecting material properties like creep resistance and corrosion. By understanding the characteristics of these particles, quality engineers can refine and improve material treatments to enhance the durability of components.
The highly regulated nature of the aerospace industry means that quality engineers cannot afford to overlook potential defects or weaknesses in component parts. Combining a wide range of imaging and analysis techniques allows them to fully understand — and consequently improve — the properties of component materials such as aluminium and nickel.
Thermo Fisher Scientific
www.thermofisher.com
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