Origin of Insignificant Strengthening Effect of CNTs in T6-Treated CNT/6061Al Composites

doi:10.1007/s40195-017-0626-z

Abstract

Abstract:

Carbon nanotube (CNT)-reinforced 6061Al (CNT/6061Al) composites were fabricated via powder metallurgy combined with friction stir processing (FSP). CNTs were dispersed after FSP and accelerated the precipitation process of the CNT/6061Al composites. However, the strengthening effect of CNTs on the T6-treated materials was insignificant, while the composites under the FSP and solution treatment conditions exhibited increased strength compared to the matrix. Precipitate-free zones (PFZs) were detected around CNTs in the T6-treated CNT/6061Al composites, and a model was proposed to describe the effect of PFZs on strength. The calculations indicated that the strength of PFZs was similar to that of the T6-treated 6061Al. As a result, the strengthening effect of CNTs on the T6-treated CNT/6061Al composites was insignificant.

Key words: Metal matrix composites, Carbon nanotubes, Precipitate-free zones

Ke Zhao, Zhen-Yu Liu, Bo-Lyu Xiao, Ding-Rui Ni, Zong-Yi Ma. Origin of Insignificant Strengthening Effect of CNTs in T6-Treated CNT/6061Al Composites[J]. Acta Metallurgica Sinica (English Letters), 2018, 31(2): 134-142.

Figures/Tables 11

Fig. 1 CNT distribution in CNT/6061Al composites: a, b SEM images of forged 1.5, 3 vol% CNT/6061Al, c, d SEM images of FSP 1.5, 3 vol% CNT/6061Al

Fig. 2 a SEM and b TEM images showing CNT distribution in 3 vol% CNT/6061Al, c, d HRTEM images showing CNT structure and CNT-Al interface

Fig. 3 Variation of hardness with aging time for 6061Al and CNT/6061Al composites

Fig. 4 XRD profiles of 3 vol% CNT/6061Al composites under different conditions

Fig. 5 TEM images showing precipitates in T6-treated CNT/6061Al composite

Table 1 Tensile properties of CNT/6061Al composites under different heat treatment conditions

CNT (vol%)	Condition	YS (MPa)	UTS (MPa)	El (%)
0	FSP	102 ± 3	190 ± 3	42 ± 1
1.5	FSP	130 ± 4	210 ± 5	31 ± 1
3	FSP	157 ± 5	253 ± 5	20 ± 2
0	Solution-treated	144 ± 3	250 ± 4	37 ± 2
1.5	Solution-treated	182 ± 3	287 ± 6	23 ± 1
3	Solution-treated	228 ± 5	317 ± 5	16 ± 1
0	T6-treated	300 ± 5	335 ± 3	28 ± 1
1.5	T6-treated	299 ± 6	353 ± 9	20 ± 2
3	T6-treated	291 ± 10	342 ± 11	14 ± 2

Fig. 6 Schematic showing the effective reinforcement changes under different conditions

Table 2 Tensile properties of FSP CNT/Al composites

CNT (vol%)	Condition	YS (MPa)	UTS (MPa)	El (%)
0	FSP	94	145	25 ± 1
1.5	FSP	133	181	20 ± 1

Table 3 V PFZ/V CNT and the percentage of PFZs with different CNT numbers in PFZs

N (Number of CNTs in PFZs)	R _N (V _PFZ/V _CNT)	P _N (Percentage)
1	16	0.37
2	12.5	0.33
3	8.7	0.19
4	7.3	0.11

Fig. 7 Calculation schematic of V PFZ/V CNT for PFZs with different CNT numbers

Fig. 8 Fracture morphology of 3 vol% CNT/6061Al composites: a, c solution-treated, b, d T6-treated

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