Mechanical Properties of Al/BN Nanocomposites Fabricated by Planetary Ball Milling and Conventional Hot Extrusion

doi:10.1007/s40195-017-0640-1

Abstract

Abstract:

In this study, Al matrix nanocomposites containing 1, 2 and 4 wt% nano-boron nitride were fabricated by mechanical milling and hot extrusion. The mechanical properties of all extruded samples were evaluated. Also, the morphology and microstructure of the milled composite powders were characterized using two types of electron microscope. The results showed that a high fraction of the boron nitride nanoparticles dissolved and formed a solid solution in Al matrix during the milling process. Through the process of solid solution formation, the work hardening rate of the composite powders increased. This led to a morphological change in the composite powders and resulted in equiaxed shape. The powder particle size also decreased after the milling process. By increasing boron nitride content within a range of 0-4 wt% in the hot extruded samples, tensile stress increased from 212 to 333 MPa. The hardness of the nanocomposite samples including 1, 2 and 4 wt% boron nitride improved approximately 55, 70 and 90% in comparison with pure Al, respectively.

Key words: Al/BN nanocomposite, Planetary ball milling, Hot extrusion, Mechanical properties, Microstructure

Reza Gostariani, Ramin Ebrahimi, Mohsen Asadi Asadabad, Mohammad Hossein Paydar. Mechanical Properties of Al/BN Nanocomposites Fabricated by Planetary Ball Milling and Conventional Hot Extrusion[J]. Acta Metallurgica Sinica (English Letters), 2018, 31(3): 245-253.

Figures/Tables 13

Fig. 1 SEM micrograph of unmilled pure Al powder

Fig. 2 TEM a, SEM b images of boron nitride nanoparticles

Fig. 3 Photograph of extruded rod billet

Fig. 4 Morphologies of pure Al a, Al/1 wt% BN b, Al/2 wt% BN c, Al/4 wt% BN d powders after 300-min milling

Fig. 5 TEM micrograph with SAD pattern of Al/4 wt% BN composite powders after 300-min milling

Fig. 6 TEM micrograph of extruded Al/1 wt% BN nanocomposite

Fig. 7 XRD patterns of Al/15 wt% BN nanocomposite under different conditions: a unmilling composite powders; b 300-min milling; c cold compaction and sintering

Fig. 8 Relative density changes of extruded samples as a function of boron nitride content

Fig. 9 Engineering stress-strain tensile curves for extruded unmilled pure Al, milled pure Al and Al/BN nanocomposites

Table 1 Quality index (QI) information from the tensile test of extruded samples

Material	UTS (MPa)	Elongation (%)	QI (MPa)
Unmilled pure Al	104	26.0	316
Milled pure Al	212	15.0	388
Al/1 wt% BN nanocomposite	297	7.7	430
Al/2 wt% BN nanocomposite	330	5.8	444
Al/4 wt% BN nanocomposite	333	1.4	355

Table 2 Comparing tensile strengths of Al/BN composites in the literature with those of the present study

References	Composition	Powder preparation	Fabrication technique	Tensile strength (MPa)	Compared to matrix (%)
[7]	Al/20 vol% BN	High-energy ball milling (20 h)	Hot press (600 °C) and hot extrusion (550 °C)	230	70
[23]	Al2124/5 wt% BN	Wet mixing	Cold compaction and hot extrusion (500 °C)	377	-9
	Al2124/10 wt% BN			311	-25
	Al2124/15 wt% BN			213	-48
[5]	Al/Mg/5 vol% BN	-	Pressure less infiltration method	390	15
[5]	Al/Mg/7.5 vol% BN		Pressure less infiltration method	416	23
[24]	Al/4.5 wt% BN nanoparticles	Wet mixing by ultrasonic	Spark plasma sintering	150	50
[22]	Al/5 wt% BN microparticles	High-energy ball milling (2 h)	Spark plasma sintering	385	130
This study	Al/1 wt% BN nanoparticles	High-energy ball milling (300 min)	Cold compaction and hot extrusion (550 °C)	297	40

Fig. 10 True stress-strain compression curves of extruded samples

Fig. 11 Micro- and macrohardness of extruded nanocomposite samples

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