Zhenya Zhang

A novel two-step processing method for fabrication of in situ Al2O3np/Al-Al11Ce3 nanocomposite

Abstract In situ Al 2 O 3np /Al-Al 11 Ce 3 nanocomposite was successfully synthesized from Al-CeO 2 system using a novel two-step processing method that combines liquid-state mechanical mixing (step-I) and sonochemistry melt reaction (step-II). The microstructural evolution and mechanical properties were investigated by optical microscopy (OM), scanning electron microscopy (SEM), transmission electron spectroscopy (TEM) and tensile tests, respectively. A good spatial distribution of CeO 2 particles in the Al melt was achieved due to reactive wetting during step-I, and the following formation of Al 2 O 3np during step-II was attributed to the cavitation-accelerated interfacial reaction. The solidified microstructure comprised uniformly dispersed Al 2 O 3np in the matrix and ultrafine lamellar Al-Al 11 Ce 3 at the grain boundaries. Such unique microstructure endowed Al 2 O 3np /Al-Al 11 Ce 3 nanocomposite with a good balance between tensile strength (175 MPa) and ductility (18.5%). The strengthening mechanisms of the nanocomposite included grain refinement, Orowan strengthening and quench strengthening, among which Orowan strengthening contributed the most to the yield strength of the nanocomposite.

Analysis of properties for in situ Al2O3p/A356 composites synthesised from the Al-SiO2 system

ABSTRACT In situ Al2O3p/A356 composites with different particle volume fractions were successfully synthesised from the Al-SiO2 system by a direct-melt reaction. γ-Al2O3 was first produced during the reaction between Al and SiO2, and the phase transformation from γ-Al2O3 to α-Al2O3 then occurred at higher temperatures (1050°C), resulting in a volume contraction. The α-Al2O3p/A356 composite exhibited a reduction in dendrite cell size that was 1.5–2 greater than for the matrix alloy cast using the same conditions. A 10% particle volume fraction yielded optimum mechanical properties, with values for the yield stress, tensile strength, elongation and microhardness of 132u2009MPa, 268u2009MPa, 5.1% and 107.2u2009HV, respectively. These corresponded to increases 50, 31, 19 and 47%, respectively, when compared to the matrix. This paper is part of a thematic issue on Light Alloys.

Zrb2 nanoparticle cluster reinforced Al matrix composites fabricated by direct melt reaction

In this work, ZrB2 nanoparticle cluster reinforced 6061Al composites were synthesized by direct melt reaction between halide salts (KBF4 and K2ZrF6) and Al. The experimental results revealed that the formation of Type III cluster (>60u2005µm, grain interior) depended on ZrB2 addition levels (>2 vol. %), whilst Type I (∼5u2005µm, grain interior) and II (5∼60u2005µm, grain/ interdendritic boundaries) were always present. The optimum tensile strength and elongation obtained in 2vol. % ZrB2/6061Al composite were substantially improved to approximately 1.52 and 2.75 times those of the 6061Al alloy. The enhanced strength was attributed to a combination effect of grain refinement (Type II cluster) and Orowan/CTE strengthening (Type I cluster). On the other hand, the impressive ductility increase was also ascribed to the presence of toughened clusters (Type I and II) that introduced the plastic slip bands and equiaxed dimples.