Microstructure and mechanical properties of a hot-extruded Al-based composite reinforced with core–shell-structured Ti/Al3Ti

International Journal of Minerals, Metallurgy and Materials, Dec 2017

An Al-based composite reinforced with core–shell-structured Ti/Al3Ti was fabricated through a powder metallurgy route followed by hot extrusion and was found to exhibit promising mechanical properties. The ultimate tensile strength and elongation of the composite sintered at 620°C for 5 h and extruded at a mass ratio of 12.75:1 reached 304 MPa and 14%, respectively, and its compressive deformation reached 60%. The promising mechanical properties are due to the core–shell-structured reinforcement, which is mainly composed of Al3Ti and Ti and is bonded strongly with the Al matrix, and to the reduced crack sensitivity of Al3Ti. The refined grains after hot extrusion also contribute to the mechanical properties of this composite. The mechanical properties might be further improved through regulating the relative thickness of Al–Ti intermetallics and Ti metal layers by adjusting the sintering time and the subsequent extrusion process.

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Microstructure and mechanical properties of a hot-extruded Al-based composite reinforced with core–shell-structured Ti/Al3Ti

Int. J. Miner. Metall. Mater. Microstructure and mechanical properties of a hot-extruded Al-based composite reinforced with core-shell-structured Ti/Al3Ti Li Zhang 0 1 Bao-lin Wu 0 1 Yu-lin Liu 0 1 0 Liaoning Key Laboratory of Aviation Light Alloy and Processing Technology, Shenyang Aerospace University , Shenyang 110136 , China 1 School of Materials Science and Engineering, Shenyang Aerospace University , Shenyang 110136 , China An Al-based composite reinforced with core-shell-structured Ti/Al3Ti was fabricated through a powder metallurgy route followed by hot extrusion and was found to exhibit promising mechanical properties. The ultimate tensile strength and elongation of the composite sintered at 620°C for 5 h and extruded at a mass ratio of 12.75:1 reached 304 MPa and 14%, respectively, and its compressive deformation reached 60%. The promising mechanical properties are due to the core-shell-structured reinforcement, which is mainly composed of Al3Ti and Ti and is bonded strongly with the Al matrix, and to the reduced crack sensitivity of Al3Ti. The refined grains after hot extrusion also contribute to the mechanical properties of this composite. The mechanical properties might be further improved through regulating the relative thickness of Al-Ti intermetallics and Ti metal layers by adjusting the sintering time and the subsequent extrusion process. microstructure; aluminum-based composites; Ti/Al3Ti; reinforcements; mechanical properties 1. Introduction Particulate-reinforced aluminum matrix composites (PRAMCs) have potential applications in the aviation, aerospace, and automotive fields because of their outstanding mechanical properties, which include high specific strength, high specific modulus, high hardness, and low thermal expansion [ 1−2 ]. PRAMCs with ceramic particles such as SiC, Al2O3, and B4C as the reinforcement material have been well developed. However, brittle layers always form between particles and the Al matrix because of chemical reactions that usually result in weakening of the interfacial bonding [3]. Reducing the harmful effect of this brittleness on the properties of such composites is an important research topic. If a casting method is used, the formation of brittle layers should be controlled through reducing chemical reactions between the particulates and the liquid. As a convenient method to fabricate Al-based composites, powder metallurgy is considered a superior method because it enables easier control of the interfacial layer. It also features other advantages such as easy adjustment of the ingredients, the ability to produce homogeneous microstructures and clean interfaces, and convenient near-net shaping [ 4−6 ]. To avoid the aforementioned brittleness, particulates with metal characteristics can be used as reinforcement; such particulates will result in decreased brittleness of the bonding layer between particulates and the Al matrix. Recently, metallic particulates such as Ni, Fe, and Ti have been added to Al matrixes to form NixAly, Al5Fe2, and Al3Ti as intermetallic reinforcements in PRAMCs through in situ reaction [ 7−10 ]. The results show that the mechanical properties of the composites were improved. Because Al3Ti exhibits a low density, a high modulus, good wear resistance, excellent specific strength, and a coefficient of thermal expansion similar to that of the Al matrix, it has attracted attention as a potential reinforcement material for Al-based composites [ 11−12 ]. Al3Ti is attractive as a component for PRAMCs used in aviation, aerospace, and automotive applications. However, the literature contains few detailed studies of the microstructure development of Al3Ti-containing PRAMCs during sintering and the effect of Al3Ti on the mechanical properties of the resultant composites. In this work, an Al-based composite was prepared through powder metallurgy and subsequent extrusion. The metallic powder Ti was chosen as the original particles to form the core–shell-structured Al3Ti reinforcement phase. The microstructure development and mechanical properties were then investigated. The mechanism of the formation of the core–shell structure is discussed. The results serve to improve the mechanical performance of Al-based composites. 2. Experimental Gas-atomized pure Ti powder with particle diameters ranging from 30 to 50 μm and pure Al powder with an average particle diameter of (2 ± 0.5) μm were chosen as the starting materials. The micrographic morphologies of the two powders were observed under a Zeiss Sigma field-emission scanning electron microscope, as shown in Figs. 1(a) and 1(b). They were mixed with a mass ratio of 30:70 (the volume fraction of Ti particles was approximately 20%) in a planetary-type grinding machine. To obtain different interfacial bonding layers, the fully mixed powders were sintered at 600, 620, or 640°C under a reduced pressure of 4.0 × 10−3 Pa or less or under an elevated pressure of 150 MPa for 5 h. The sintering (...truncated)


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Li Zhang, Bao-lin Wu, Yu-lin Liu. Microstructure and mechanical properties of a hot-extruded Al-based composite reinforced with core–shell-structured Ti/Al3Ti, International Journal of Minerals, Metallurgy and Materials, 2017, pp. 1431-1437, Volume 24, Issue 12, DOI: 10.1007/s12613-017-1536-9