Fabrication of Al/AlN in-situ nanocomposite through planetary ball milling and hot extrusion of Al/BN: Microstructural evaluation and mechanical behavior

Abstract

In this study, Al/AlN in-situ nanocomposites were fabricated using Al/BN as the starting composite powders. The impact of adding hexagonal boron nitride (BN) to the Al matrix of commercial purity on the microstructure and mechanical behavior of the fabricated in-situ nanocomposites was investigated. Samples including 1, 2, and 4 wt.% boron nitride nanoparticles were produced by planetary ball milling of the composite powders and a post-process of hot extrusion. Scanning transmission electron microscopy revealed that boron nitride nanoparticles dissolved as a solid solution of B and N in the Al matrix at the as-milled state. Through the process of hot extrusion, AlN as the in-situ phase was formed by a reaction between Al and N. These led to improve the mechanical properties as well as grain refinement of Al/AlN nanocomposite. The average grain size of the fabricated composites with the use of 1, 2 and 4 wt.% BN was measured about 910, 823, and 760 nm respectively. It was found that combined strengthening mechanisms of grain refinement, a solid solution of mostly B and AlN in-situ phase formation improved the mechanical properties of Al/AlN nanocomposite. With the use of 1, 2, and 4 wt.% BN, the tensile strength of nanocomposite samples increased approximately 40, 56, and 57% in comparison with pure Al, respectively. The remarkable change in microstructure and mechanical properties of the nanocomposite was obtained when the content of BN is up to 2 wt.%.

Dispersion and Preparation of Nano-AlN/AA6061 Composites by Pressure Infiltration Method

“…In the as-cast material, a relatively coarse struc-ture was observed in the composite material, and the composite material after HE was considerably refined to form a dense structure with a regular arrangement. The nano-AlN benefits from the arranged uniform and refined microstructures in terms of improved strength [30,31]. In the process of creating high-energy ball milling powder, we control the cold-welding phenomenon of the powder by adding alcohol as a process control agent, which can improve the ball milling efficiency and avoid the problem of nano-AlN agglomerating during ball milling.…”

“…In the as-cast material, a relatively coarse structure was observed in the composite material, and the composite material after HE was considerably refined to form a dense structure with a regular arrangement. The nano-AlN benefits from the arranged uniform and refined microstructures in terms of improved strength [30,31]. Figure 5 displays the XRD pattern of the 3 wt.% nano-AlN/AA6061 composite material in as-cast and as-extruded conditions.…”

Transmission Electron Microscopy of Nanomaterials

“…It is well recognized that BN decomposed and dissolved in the Al matrix during high energy ball milling. Then, the possible AlN and AlB 2 as the in-situ phases are generated during a heating state in the Al matrix [10][11][12][13][14][15][16][17]. Due to presence of in-situ particles in matrix, the microstructural observation and mechanical behavior of the in-situ Al/BN nanocomposite should be investigated by high resolution transmission electron microscopy.…”

Effect of Cold and Warm Rolling on the Particle Distribution and Tensile Properties of Heterogeneous Structured AlN/Al Nanocomposites

“…As an important part of metal matrix composites, aluminum matrix composites (AMCs) provide a combination of low density, high strength, excellent wear resistance and corrosion resistance for automotive industries and aerospace applications [ 1 , 2 , 3 , 4 ]. Particularly, aluminum matrix composites with different microstructural design by in situ fabrication such as melting methods and spark plasma sintering (SPS) are popular owing to their advantages [ 5 , 6 , 7 , 8 ]. However, the purpose is always to obtain a uniform distribution of reinforcement regardless of which processing method.…”