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Aluminum and A356 alloy foam castings are produced using a melt-foaming method. Prior to foaming, the melt is modified with nano-sized particles (SiC, TiN, or Al2O3). The nano-sized particles are mixed with micro-sized Al particles, which are ultrasonically treated and hot-extruded. Thus, the so-called "modifying nano-composition" is obtained. The resulting compositions are introduced into the melt of the Al foam at the following mass concentrations of nanoparticles: SiC: 0.038 wt. %; TiN: 0.045 wt. %; and Al2O3: 0.046 wt. %. For the A356 foam, we use the following concentrations: SiC: 0.039 wt. %; TiN: 0.052 wt. %; and Al2O3: 0.086 wt. %. The macrostructure of the foam castings is investigated by CT scanning and 3D analysis. The pore size distributions and accumulative fraction dependencies are determined for all samples. The microstructure of the foam castings is investigated by SEM-EDS analysis. The results confirmed the presence of individual nano-sized particles, as well as clusters of particles in foam walls. The conducted compression tests show a significant increase in the plateau stress (up to 237%) of the modified aluminum foam castings compared to non-modified castings. However, a similar effect of the nano-compositions on A356 alloy foam castings is not observed. The obtained results show that the above-indicated concentrations of nanoparticles can positively influence the mechanical properties of aluminum foam castings. The novelty of the current study is two-fold: (1) such low concentrations of added nanoparticles have never been used before to alter Al foam's properties, and (2) an original method of introducing the nanoparticles into the melt is applied in the form of nano-compositions. [ABSTRACT FROM AUTHOR]

The purpose of this research is to characterize compacted and extruded specimens made of aluminium alloys chips using micro computed tomography technique. Specimens were prepared through cold and hot compaction, which yield two types of so-called "compacts". After that the compacts were subjected to hot extrusion to obtain the final extruded products. Results show that, depending on the type of alloy, porosity of compacts varies between (a) 4.55 % and 14.28 % for cold-compacted specimens and (b) between 0.15 % and 2.79 % for hot-compacted specimens. Porosity of extruded specimens is close to zero. It is concluded that the results of this study provide a good basis for further research aimed at finding the optimal process parameters for compaction and extrusion. [ABSTRACT FROM AUTHOR]

A method for determining the thermal conductivity coefficient of a foam material of A356 aluminum alloy has been proposed. The foam material has been produced by decomposition of titanium hydride introduced into the melt and subsequent cooling and crystallization. During the process, the measurement of temperature dependences on time has been performed at two selected points of the foam casting. The problem of heat transfer and crystallization of the casting and mold is solved by means of mathematical model proposed. The experimental data and the corresponding solutions of the mathematical model have been used for the realization of an identification procedure for determining the coefficient of thermal conductivity of the foam material and the coefficient of heat transfer at the casting-mold boundary. Through the represented methodology new data for important thermophysical characteristic are obtained. [ABSTRACT FROM AUTHOR]

Comparative study of the impact of modification by standard modifier phosphorus (P), nanodiamonds (ND) or nanosized SiC powder on the microstructure and corrosion behavior of hypereutectic alloy AlSi18 was carried out. Data were obtained on the refinement of silicon crystals in the structure of the modified alloys. Gravimetric tests for evaluation of uniform corrosion (UC) were carried out and the corrosion rate for each of the modified and nonmodified alloys was determined. Increase of the UC rate in the range from 13 % to 84 % was found after modification, the value depending on the type of modifier. The mechanisms of propagation of pitting (PC) and intergranular corrosion (IGC) were studied and data for IGC penetration depth were obtained. It was established that no typical PC developed both in non-modified and modified AlSi18 alloys and the corrosion process run manly in depth like localized IGC. [ABSTRACT FROM AUTHOR]