Wear Characteristics of Mg Alloy AZ91 Reinforced with Oriented Short Carbon Fibers

Abstract

Light-weight metal matrix composites, especially magnesium-based composites, have recently become more widespread for high-efficiency applications, including aerospace, automobile, defense, and telecommunication industries. The squeeze cast AZ91 base material (AZ91-BM) and its composites having 23 vol.% short carbon fibers were fabricated and investigated. The composite specimens were machined normal to the reinforced plane (Composite-N) and parallel to the reinforced plane (Composite-P). All the as-casted materials were subjected to different tests, such as hardness, compression, and wear testing, evaluating the mechanical properties. Dry wear tests were performed using a pin-on-disk machine at room temperature under different applied wear loads (1–5 N) and different sliding distances (0.4461×104–3.12×104 m). The microstructures and worn surfaces of the fabricated AZ91-BM and the two composite specimens were investigated using a scanning electron microscope (SEM) equipped with an energy dispersive spectroscopy (EDS) advanced analysis system. The wear debris was collected and investigated also under the SEM. The results showed significant improvement in hardness, compressive strength, and wear resistance of the composite specimens (Composite-N and Composite-P) over the AZ91-BM. The compressive strength and wear resistance are more fibers orientation sensitive than the hardness results. When the fiber orientation is parallel to the sliding direction (Composite-N), the weight loss is somewhat lower than that of the fiber orientation perpendicular to the sliding direction (Composite-P) at a constant wear load of 2 N and the sliding distances of 0.4461×104, 1.34×104 , and 2.23×104 m. In contrast, the weight loss of Composite-P is lower than Composite-N, especially at the highest sliding distance of 3.12×104 m due to the continuous feeding of graphite lubricant film and the higher compressive strength. Plastic deformation, oxidation, and abrasive wear are the dominant wear mechanisms of AZ91-BM; in contrast, abrasive and delamination wear are mainly the wear mechanisms of the two composites under the applied testing conditions.

Tribological aspects of magnesium matrix composites: A review of recent experimental studies

“…The fibre fracture is attributed to the difference in CTE of the Mg matrix and carbon fibres.

Figure 13 SEM images of the composite-N, (a) VCD, (b) EDT and composite-P, (c) VCD and (d) EDT [64].

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“…As a result, the pull-out of carbon fibres leads to material loss.

Figure 18 Weight loss graph of the AZ91/SCF composites [64].

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“…Figure 33 also shows the dominant wear mechanisms of Mg matrix composites depending on different loads and sliding speeds.

Figure 32 Worn surface images of the samples (a,b) AZ91 alloy (c) composite-N and (d) composite-P [64].

Figure 33 Wear mechanisms depend on sliding speed and load for Mg matrix composites.

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“…Ataya et al [64] produced the AZ91/SCF composites by squeeze casting. Figure 13 shows the SEM images of the samples.…”

Characterization and Modelling of Manufacturing–Microstructure–Property–Mechanism Relationship for Advanced and Emerging Materials

“…The mechanical testing showed higher-bearing tensile shear loads in all the refilled FSSW joints than those that were given by the as-received FSSW joints. In order to improve the mechanical and tribological performances of an AZ91 Mg alloy, Ataya et al [ 31 ] added short carbon fibers to the AZ91 matrix. They observed a large influence of the carbon fibers’ orientation on both the compressive strength and the wear resistance of the Mg composite; however, they did not observe an obvious difference in the hardness.…”