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The present study (part B) is a direct continuation of the leading study (part A), in which we had introduced extruded aluminum (Al) + 8.8 and 14.7 vol% aluminum nitride (AlN) metal matrix composites (MMC) manufactured at a cost-effective industrial scale and targeted for structural load-bearing applications with an expected service at elevated temperatures. In the leading study the processing, microstructure of nitrided and extruded Al-AlN MMC and the thermal stability of the extruded Al-AlN MMC as reflected in changes to their tensile mechanical properties induced by annealing up to 600 °C were elaborated. In the present ensuing study we discussed in details the mechanical, thermal and creep properties, active strengthening mechanisms, and microstructure-property relations of Al-AlN MMC annealed at 500 °C for 24 h, which were examined in a broad temperature range of 22–500 °C. In addition to increased Young's modulus Al-AlN MMC showed high tensile strengths determined at 300 °C, which were superior to any conventional Al alloy, accompanied with reasonably high ductility. At the same time Al-AlN MMC preserved excellent creep performance, which was superior to the heat resistant reference alloys, reduced coefficient of thermal expansion and reasonable thermal conductivity. The results confirmed that reported thermally stable Al-AlN MMC may be considered a promising material with an appealing set of the properties directed for load-bearing structural applications with an expected service at elevated temperatures. • in-situ Al-AlN MMC fabricated by cost-effective approach realized at a large scale. • The mechanical, thermal and creep properties of Al-AlN MMC determined at 22–500 °C. • Active strengthening mechanisms and microstructure-property relations discussed. • An attractive set of the properties at 300 °C superior to conventional Al alloys. • A promising material for structural applications with service at high temperatures. [ABSTRACT FROM AUTHOR]

• In-situ Al-AlN MMCs fabricated by cost-effective approach realized at a large scale. • The Al+Mg+Sn powder blanks nitrided in a gaseous N 2 followed by a hot extrusion. • The microstructure of extruded MMCs consisted of Al grains with the size of ~1.8 µm. • The Al grains decorated by the evenly dispersed areas rich in AlN nanocrystals. • The stable AlN dispersoids effectively stabilized Al grain structure up to 500 °C. This study introduces in-situ aluminum (Al)-aluminum nitride (AlN) metal matrix composites (MMCs) manufactured by a powder metallurgy (PM) cost-effective approach realized at a large industrial scale. The Al-AlN MMCs were targeted for structural load-bearing applications with an expected service at elevated temperatures not normally associated with a use of conventional Al-based alloys and MMCs. Commercial Al, magnesium, and tin powders were processed by readily available PM techniques of blending, cold isostatic pressing (CIP), a solid-state nitridation in a static gaseous nitrogen, and a hot direct extrusion. Two sound voids free Al + 8.8 and 14.7 vol% AlN MMCs were reproducibly fabricated in a form of the long extruded bars with the cross-section of 80 × 15 mm. The microstructure of nitrided and extruded MMCs was presented in details. A typical yolk-shell-like microstructure of Al metallic core and nitrided layer was formed homogenously in a volume of the CIP bulky (~25 kg) billets upon nitridation. The microstructure of extruded Al-AlN MMCs consisted of Al grains elongated into the extrusion direction. The Al grain structure was embedded with the evenly distributed micrometric regions formed by a high density AlN nanocrystals in Al matrix. A stability of the tensile mechanical properties of as-extruded Al-AlN MMCs was pursued in transversal and longitudinal directions after the annealings performed at 300–600 °C for 24 h. Owing to an effective stabilization by the stable and fine AlN dispersoids by Zener pinning action no major changes to the mechanical properties took place after annealing up to 500 °C. [ABSTRACT FROM AUTHOR]

Bulk Al materials with average grain sizes of 0.47 and 2.4 µm, were fabricated by quasi-isostatic forging consolidation of two types of Al powders with average particle sizes of 1.3 and 8.9 μm, respectively. By utilizing the native amorphous Al 2 O 3 (am-Al 2 O 3 ) film on the Al powders surfaces, a continuous, ∼7 nm thick, am-Al 2 O 3 network was formed in situ in the Al specimens. Systematic investigation of the changes to the am-Al 2 O 3 network embedded in the Al matrix upon heating and annealing up to 600 °C was performed by transmission electron microscopy (TEM). At the same time, the stability of the Al grain structure was studied by transmission Kikuchi diffraction (TKD), electron back-scatter diffraction (EBSD), and TEM. The am-Al 2 O 3 network remained stable after annealing at 400 °C for 24 h. In-situ TEM studies revealed that at temperatures ≥450 °C, phase transformation of the am-Al 2 O 3 network to crystalline γ-Al 2 O 3 particles occurred. After annealing at 600 °C for 24 h the transformation was completed, whereby only nanometric γ-Al 2 O 3 particles with an average size of 28 nm resided on the high angle grain boundaries of Al. Due to the pinning effect of γ-Al 2 O 3 , the Al grain and subgrain structures remained unchanged during annealing up to 600 °C for 24 h. The effect of the am-Al 2 O 3 →γ-Al 2 O 3 transformation on the mechanical properties of ultrafine- and fine-grained Al is discussed from the standpoint of the underlying mechanisms. [ABSTRACT FROM AUTHOR]

Abstract: The rapidly solidified AlCr4.7Fe1.1Si0.3 (at.%) alloy produced at large scale by direct extrusion of gas atomised powders was investigated. Hot-extrusion yielded sound compacts and did not create any major structural changes compared to the as-atomised state. Microstructural characterisation of the as-extruded material revealed submicron scale α-Al grains with an embedded Al7Cr crystalline phase and traces of a nano-scale quasicrystalline Al84.6Cr15.4 phase. The long-term thermal stability up to 300°C of compacts was proven. The thermal stability of compacts was accompanied by high mechanical properties, especially high strength and Young''s modulus, and creep performance up to 300°C. The same material was prepared by laboratory scale extrusion of cryo-chopped melt-spun ribbons as a reference material. No major differences in the structure or properties of the industrially prepared material were observed compared to the reference material. [Copyright &y& Elsevier]