Improvement of the Mechanical Properties of Al-Si Alloys by TiC Nanoparticles
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METAL strengthening is one of the main challenges encountered in materials technology. Traditionally, such strengthening was achieved by alloying with other chemical elements or compounds, but relatively high fractions of relatively expensive materials were needed to obtain the required technological characteristics, and the results achieved were still far from satisfactory. The growing interest in Al-Si cast alloys is due to their widespread and extensive use in automotive, aerospace, and transport systems. One of these alloys is A356 alloy, which has excellent castability, mechanical characteristics, and physical properties. The strength of the alloy can be improved by alloying,[1–6] by means of master alloys, by heat treatment, or by applying ultrasound that affects the crystallization process.[7–9] There are reports of TiB2 particles being utilized, which serve as crystallization nuclei and cause refinement of the metal grains.[10,11] Small addition of strontium and sodium into Al-Si casting alloys enhance the formation of refined eutectic colonies.[12,13] Another relatively new strengthening technology is semisolid metal processing (SSM), which was initially developed by researchers at MIT in the 1970s.[14] In the
KONSTANTIN BORODIANSKIY, Researcher, is with the Laboratory for Metal and Ceramic Coatings and Nanotechnology, Materials Research Center, Ariel University, Science Park, 40700 Ariel, Israel, and also with Department of Chemistry, Bar-Ilan University, 52900 Ramat Gan, Israel. Contact e-mail: konstantinb@ ariel.ac.il ALEXEY KOSSENKO, Researcher, and MICHAEL ZINIGRAD, Professor and Head, are with the Laboratory for Metal and Ceramic Coatings and Nanotechnology, Materials Research Center, Ariel University. Manuscript submitted March 17, 2013. METALLURGICAL AND MATERIALS TRANSACTIONS A
SSM approach, metals are treated by a mixture of fine solid nonmetal particles dispersed in the liquid.[15–18] Nanotechnology is also used in the metal-strengthening processes. It would be logical to expect that nanosized particles would cause similar changes in mechanical properties, but that their influence would be ‘‘milder’’ and more balanced. Indeed, it has been established that the mechanical properties of Al A356 could be improved by adding Al2O3 nanoparticles in a minute concentration of 1 wt pct during casting.[19] In the current article, we report the influence of ceramic nanoparticles on the mechanical properties of Al-Si alloy A356. One of the serious technological problems associated with the introduction of these particles into the molten metal is the poor wettability of the former by the latter. We also report here a method for solving this problem by severe mechanical loading of the metal matrix with titanium carbide nanoparticles pretreated by mechanochemical activation. The assumption that the grain-size-strengthening mechanism acts in the process is discussed in the current article.
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EXPERIMENTAL
Al-Si alloy A356 (Rheinfelden Alloys GmbH) was used as a bulk material. The composition of the alloy is g
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