Materials science communicationCharacterization of 2024-T3: An aerospace aluminum alloy
Introduction
Advanced aluminum alloys for aerospace application are required to possess high fracture toughness, high fatigue performance, high formability, and superplasticity to meet the needs for lower structural weight, higher damage tolerance, and higher durability [1]. The heat-treatable 2024-T3 aluminum alloy, reported in this investigation, has attractive features of high strength and that its ductility does not significantly decrease during the strengthening heat treatment [2], [3], [4].
Microstructural characterization of metals and alloys usually employs optical and electron microscopy. Recent advances in scanning electron microscopy (SEM) enable us to conduct not only microstructural characterization but also precise elemental analysis with the aid of an electron probe micro-analyzer (EPMA) linked to the SEM [5], [6], [7]. An electron probe micro-analyzer (EPMA) is a microbeam instrument used primarily for the in situ non-destructive chemical analysis of minute solid samples. It is an analytical technique that is used to establish the composition of small areas on specimens. EPMA is one of several particle-beam techniques. Particular, although not unique, to EPMA is bombardment of the specimen with a beam of accelerated electrons. The electron beam is focused on the surface of a specimen using a series of electromagnetic lenses, and these energetic electrons produce characteristic X-rays within a small volume (typically between 1 and 9 μm3) of the specimen [8].
The research reported in present paper presents microstructural and material characterization of ALCLAD sheet conforming to 2024-T3 aluminum alloy through metallographic investigations, optical microscopy, SEM, and EPMA techniques. ALCLAD is the aluminum alloy sheet coated with pure aluminum with coating thickness up to 0.01 mm; it is produced by sandwiching the base metal (2024-T3 aluminum alloy) between pieces of the coating metal (pure aluminum) and the sandwich is then rolled to the required thickness [9]. The ALCLAD 2024-T3 aerospace aluminum alloy (sheet) is extensively used in the skin of the C-130 Hercules aircrafts [10].
Section snippets
Experimentation
The starting material (SM) was in the form of ALCLAD sheet conforming to the 2024-T3 aluminum alloy; and was acquired from a local aerospace industry: Royal Malaysian Air Force (RMAF). Metallographic specimen for the SM was prepared by sectioning a small sample with scissors followed by coldmounting. The sample was ground by using emery papers on a metallographic grinding machine. Polishing was done with high-alumina powder on a metallographic polishing machine. The metallographic sample was
Results and discussion
The microstructures of the as-received material are shown as scanning electron micrograph (SEM) and optical micrograph in Fig. 1(a, b), respectively. Fig. 1(a) presents the SEM micrograph for the aluminum alloy; which clearly shows precipitation of second-phase of θ′ phase in the aluminum matrix. The optical micrograph showing the multi-phase microstructure of the 2024-T3 aluminum alloy is shown in Fig. 1(b); this micrograph not only shows the α and θ phases but also the θ′ precipitates
Conclusions
The optical and scanning electron microscopy (SEM) for the investigated aluminum alloy enables us to confirm that the alloy had been heat treated according to the 2024-T3 three-stage treatment (solution treatment, cold-working, and tempering). The measured grain size (19.6 μm) and the interpretation of microstructures for the alloy led us to conclude that the alloy possesses good tensile strength. The analysis of elemental map from EPMA for the 2024-T3 aluminum alloy (ALCLAD sheet) confirmed the
Acknowledgements
The authors are grateful to the Royal Malaysian Air Force (RMAF) for providing the research material: 2024-T3 aluminum alloy (ALCLAD sheet). The authors are also thankful to the Department of Geology, University of Malaya for permitting use of Electron Probe Micro Analyzer (EPMA).
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