Enhancing Wear Resistance of A356 Alloy by Adding CNFs Based on Ultrasonic Vibration Casting

doi:10.1007/s40195-017-0680-6

Abstract

Abstract:

A356-carbon nanofibers (CNFs) composites with different contents of CNFs were fabricated by ultrasonic vibration casting to investigate the effect of CNFs in the matrix on the mechanical properties and wear resistance. The worn surfaces were investigated using scanning electron microscopy (SEM). As the CNFs content was increased, strength, hardness and wear resistance were significantly enhanced and the coefficient of friction was extremely reduced. The nanocomposite containing 1.2 wt% of CNFs exhibited more than 109 HV in hardness and less than 0.35 in the coefficient of friction. Compared with the as-cast matrix, the wear rate of the optimal composite was less than one-third of the matrix sample and the microhardness exhibited about 47% enhancement of the matrix. Meanwhile, steadier and lower friction coefficient was also achieved by the composite. CNFs were observed to be either partially or fully crushed forming a carbon film that covered the surface and acted as a solid lubricant, enhancing the wear behavior significantly.

Key words: A356 matrix composites, Carbon nanofibers, Wear testing

Qing-Jie Wu, Hong Yan, Peng-Xiang Zhang, Xue-Qin Zhu, Qiao Nie. Enhancing Wear Resistance of A356 Alloy by Adding CNFs Based on Ultrasonic Vibration Casting[J]. Acta Metallurgica Sinica (English Letters), 2018, 31(5): 523-532.

Figures/Tables 14

Table 1 Chemical composition of A356 alloy (wt%)

Al	Si	Mg	Fe	Zn	Mn	Cu
Bal.	7.1	0.46	0.11	0.06	0.05	0.03

Fig. 1 SEM image of CNFs

Fig. 2 Microstructures of the 0.9 wt% CNFs/A356 nanocomposites fabricated by a mechanical stirring, b high-intensity ultrasonic treatments

Fig. 3 SEM a, TEM b images of CNFs in the composites

Table 2 Tensile properties and Vickers hardness of CNFs/A356 nanocomposites prepared with different CNFs contents

Materials	YS (MPa)	UTS (MPa)	Elongation (%)	Vickers hardness (HV)
A356	145 ± 4	214 ± 4.42	6 ± 0.42	74 ± 3.9
A356 + 0.3 wt%	151 ± 3.62	217 ± 5.21	5.8 ± 0.49	82 ± 4.3
A356 + 0.6 wt%	176 ± 3.86	242 ± 4.38	5.52 ± 0.43	90 ± 4.23
A356 + 0.9 wt%	202 ± 4.4	261.2 ± 6.26	5.1 ± 0.36	106 ± 4.1
A356 + 1.2 wt%	200 ± 4.93	254.1 ± 5.74	3.9 ± 0.25	109 ± 3.75

Fig. 4 TEM image of dislocations found in the nanocomposites

Fig. 5 Wear rate versus CNF wt% a. Variations of coefficient of friction as a function of CNFs content: b A356 matrix, c 0.3 wt% CNFs/A356, d 0.6 wt% CNFs/A356, e 0.9 wt% CNFs/A356, f 1.2 wt% CNFs/A356

Table 3 Comparison of the dry sliding wear rates of A356 composites reinforced with different reinforcements

Investigators	Test configuration	Test conditions	Materials	Wear rate (10^-3 mm³/m)	Optimization ratio (%)
Rohatgi et al. [25]	Pin on disk	v = 1.0 m/s L = 2.97 N t = 300 s	A356 A356 + 5 vol.% fly ash particles	70 51.3	26
Cree and Pugh [26]	Ball on disk	L = 20 N v = 33 mm/s	A356 A356 + 12 vol.% SiC foam	28 25	10.7
Present authors	Pin on disk	v = 0.188 m/s L = 40 N t = 900 s	A356 A356 + 1.2 wt% CNFs	21.3 13	39

Fig. 6 SEM images of the friction surfaces of nanocomposites after friction tests: a, b A356 matrix, c, d 0.3 wt% CNFs/A356, e, f 0.6 wt% CNFs/A356, g, h 0.9 wt% CNFs/A356, i, j 1.2 wt% CNFs/A356

Fig. 7 X-ray elemental maps of the worn surface for 1.2 wt% CNFs/A356 nanocomposite after friction test

Fig. 8 Schematic presentation of the wear mechanism of A356-CNFs

Fig. 9 Wear rate of the A356-1.2 wt% CNF composite under different applied loads a; friction coefficient for A356/1.2 wt% CNFs at b 20 N, c 40 N, d 60 N

Fig. 10 SEM micrographs of the worn surfaces of A356/1.2 wt% CNFs at a load of a 20 N, b 40 N, c 60 N

Fig. 11 CNFs on the worn surfaces of A356/1.2 wt% CNFs composites after friction tests: a 60 N, b 40 N

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