Synthesis and Characterization of Al Reinforced with Al₄C₃ Nanoparticles Produced by Mechanical Milling

Abstract

Mechanical alloying technique, such high energy ball milling process, is suitable for producing composite metal powders with a fine controlled microstructure. This method is crucial for obtaining homogeneous distribution of nano-sized dispersoids in a more ductile matrix (e.g. aluminium-or copper based alloys). The reinforcing particles Al4C3 have become an interesting reinforcing material because their high level of physical and mechanical properties, e.g. high temperature strength, thermal cyclic resistance, wear resistance and low linear expansion coefficient. Therefore, the reinforcement of the aluminum using Al 4 C 3 has recently become the subject of many studies and widely used for products and structures [1,2].The Al-based composites were produced by mixing Al powder (99.5 % purity) with 1 and 2 wt. % of Al 4 C 3 nanoparticle powder (previously synthetized by mechanical milling and subsequent heat treatment), each Al-Al 4 C 3 mixtures powder were mechanically milled in a high energy Simoloyer mill during 8 h. Argon was used as the milling atmosphere and ~4 ml methanol as a process-control agent. The device and milling media used were made from hardened steel. The milling ball to powder weight ratio was set to 50:1. Consolidated samples were obtained by pressing the powder mixtures during 20 s at 350 MPa in uniaxial load. The consolidate sample was sintered during 2h at 650°C. The Al4C3 reinforcing phase dispersed into the aluminum matrix also was observed by using electron microscopy analyses. Fig. 1a shows a STEM bright-field image of Al-20 sample (2 wt. % of Al 4 C 3 and not sintered), the image shows a graphite nanoparticle of about 10 nm long which is close to an Al4C3 nanoparticle that shows an irregular shape present in the aluminum matrix. Fig. 1b shows the simulated image that shows the interplanar distance of the A selected area of a Al 4 C 3 nanoparticle and the interplanar distance of the B selected area of a graphite nanoparticle. The Fig. 2a shows a STEM bright-field representative image of a rod-shaped aluminum carbide nanoparticle of about 100 nm long and 10 nm wide in the Al matrix of Al-22 sample (2 wt. % of Al 4 C 3 and sintered during 2 h). The HRTEM image of Figure 2b shows the interplanar distances of a rod shaped particle which correspond to Al 4 C 3 compound. At seems the Al 4 C 3 irregular shape nanoparticles dispersed into the Al matrix during the mechanical milling change to a regular rod-shaped after the sintering process.

Structural proprieties of the Al–Al 4 C 3 nanocomposite produced via mechanical alloying and annealing

“…Using mechanical alloying subsequent annealing process, Al 4 C 3 -reinforced aluminium was successfully fabricated [1,3,[7][8][9][10][11][12][13][14]. It was noted that Al 4 C 3 is the responsible of reinforcing [2,13].…”

“…Nanocomposite offers significant enhancement properties of materials due to the non‐metric reinforcement better than microcomposite. On the other hand, Al 4 C 3 show a high‐temperature strength, thermal cyclic resistance, wear resistance and low linear expansion coefficient [7]. Which make the production of the nanocomposite of an aluminium matrix reinforced by Al 4 C 3 very interesting.…”