Strength and Wear Behavior of Mg Alloy AE42 Reinforced with Carbon Short Fibers

doi:10.1007/s40195-018-0771-z

Abstract

Abstract:

In addition to the advantage of the lightweight of magnesium alloys, magnesium composites have moderate strength and elastic modulus. The proposed application of magnesium composites as diesel truck pistons makes it necessary to assess their wear performance. Little research data have been discussed on wear behavior of Mg alloy AE42 matrix and its composites. Thus, this paper reports wear behavior of magnesium alloy AE42 (Mg-Al-Mn—RE; rare earth) and its composite AE42-C, which contains 23 vol% of randomly oriented carbon short fibers. Materials characterization, including density measurements, hardness testing, microstructures investigation, and compression testing at temperatures of 25, 150, and 300 °C, were conducted. Wear tests were performed under various loads and sliding distances. Wear mechanisms were also proposed based on the examination of worn surfaces using optical microscopy and scanning electron microscopy equipped with EDX (energy-dispersive X-ray spectrometry) analysis system. The hardness of AE42-23 vol% C composite is twice the hardness of the Mg matrix alloy AE42. Significant improvements to yield stress and compressive strength at temperatures of 25, 150, and 300 °C of the composite versus the AE42 alloy are achieved. Wear resistance of the composite is improved considerably versus that of the Mg alloy AE42 at the various sliding distances. Smearing of graphite on the worn surface produces a lubricating film that delays change from mild to severe wear of the composite, especially at high loads. EDX analysis of the worn surface shows oxidation of the matrix alloy at higher wear loads, and this mechanism decreases in the presence of carbon fibers under the same loads. Abrasive wear, oxidation, and plastic deformation are the dominant wear mechanisms for the alloy matrix AE42, whereas mainly abrasive wear is the wear mechanism of AE42-23 vol% C composite under the proposed testing conditions.

Key words: Magnesium composites, Carbon short fibers, Compressive strength, Wear resistance, Wear mechanisms

Sabbah Ataya, Naser A. Alsaleh, Mohamed M. El-Sayed Seleman. Strength and Wear Behavior of Mg Alloy AE42 Reinforced with Carbon Short Fibers[J]. Acta Metallurgica Sinica (English Letters), 2019, 32(1): 31-40.

Figures/Tables 17

Table 1 Chemical composition (wt%) of magnesium matrix material (AE42)

Al	Zn	Mn	Ce	La	Nd	Pr	Th	Mg
3.93	0.01	0.30	1.20	0.60	0.40	0.10	0.26	Bal.

Table 2 Nominal chemical composition and physico-mechanical properties of the carbon short fibers [23]

Nominal composition (wt%)	Density (g/cm³)	Tensile strength (GPa)	Elastic modulus (GPa)	Strain to failure (%)
>?95 C	1.76	2-3.5	230-400	1.2-1.5

Fig. 1 Pin-on-bush wear testing machine

Table 3 Density and hardness of Mg alloy AE42 and its composite AE42-C

Material	Theoretical density (g/cm³)	Bulk density (g/cm³)	Relative density (%)	Hardness (HV)
AE42 alloy	1.80	1.69	94	46.8
AE42-23 vol% C	1.79	1.72	96	91.2

Fig. 2 Optical microstructure images of a Mg alloy AE42, b AE42-C composite

Fig. 3 Nominal stress strain curves of a AE42, b AE42-C

Fig. 4 Compression test results at various test temperatures for AE42 and AE42-C: a compressive yield stress, b compressive strength

Fig. 5 Weight loss versus applied wear load for Mg alloy AE42 and its composite AE42-C, which contains 23 vol% carbon short fibers

Fig. 6 Weight loss versus running distance for AE42 and AE42-C

Fig. 7 Wear rate versus sliding distance for AE42 and AE42-C under a wear load of 3.14 N

Fig. 8 Magnified worn surface of the AE42 alloy under wear load of 9.81 N and sliding distance of 8.92 km

Fig. 9 Worn surface under a wear load of 3.14 N and sliding distance of 8.92 km: a AE42, b AE42-C

Fig. 10 a Worn surface of AE42-C under a wear load of 9.81 N and sliding distance of 8.92 km, b higher magnification of a

Fig. 11 EDX analysis of worn surface of AE42 under a wear load of 2.45 N for a sliding distance of 8.9 km

Fig. 12 EDX analysis of the worn surface of AE42 under a wear load of 4.9 N for a running distance of 8.9 km

Fig. 13 EDX analysis of the worn surface of AE42-C composites under a load of 4.9 N for a wear distance of 8.9 km

Table 4 EDX analysis (wt%) of various spots shown in the micrograph in Fig. 13 for AE42-C under wear load of 4.9 N for sliding distance of 8.9 km

Elements (wt%)	Spot 1	Spot 2	Spot 3	Spot 4	Spot 5	Spot 6
Mg	100.0	64.88	-	11.38	68.33	72.78
Al	-	12.59	-	-	-	-
O	-	22.53	-	-	31.67	27.22
C	-	-	100.0	88.62	-	-

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