Solid State Phenomena Vol. 191

Abstract: At present both primary and secondary aluminium needs to be refined before further treatment. This can be done by barbotage process, so blowing small bubbles of inert gas into liquid metal. This way harmful impurities especially hydrogen can be removed. Barbotage is very complex taking into consideration hydrodynamics of this process. Therefore modelling research is carried out to get to know the phenomena that take place during the process better. Two different modelling research can be applied: physical and numerical. Physical modelling gives possibility to determine the level of gas dispersion in the liquid metal. Whereas, numerical modelling shows the velocity field distribution, turbulent intensity and volume fraction of gas. The paper presents results of physical and numerical modelling of the refining process taking place in the bath reactor URO-200. Physical modelling was carried out for three different flow rate of refining gas: 5, 10 and 15 dm3/min and three different rotary impeller speeds: 0, 300, 500 rpm Commercial program in Computational Fluid Dynamics was used for numerical calculation. Model VOF (Volume of Fluid) was applied for modelling the multiphase flow. Obtained results were compared in order to verify the numerical settings and correctness of the choice.

Abstract: Today aluminium obtained from ores (primary) and from scrap (secondary) need to be refined. During this process harmful impurities such as hydrogen, sodium, lithium, oxides, borides or carbides can be removed. There are many different ways of aluminium refining process. The most popular seem to be barbotage that means blowing through aluminium many tiny gas bubbles of refining gas. Reactors applying this methods have been working all over the word. They are of different types: bath and continuous, using ceramic porous plugs, special kinds of nozzles or rotary impeller for generating small gas bubbles. At present reactors for continuous refining have become the most popular. In Poland typical representative of such reactors is URC-7000 reactor. The phenomena occurring during this process are rather complicated. Therefore to know them better the modelling research is applied, especially physical modelling. The paper presents the results of such a research. The tests were carried out in the test stand for modelling the babotage process in the URC-7000 reactor. The different modelling agents were tested (water, glycerin and mixture of water and glycerine). The density and viscosity of water and glycerin mixture were determined. Modelling tests were conducted for four different flow rates of refining gas: 6, 10, 15 and 20 dm3/min. Results were registered by digital camera. Pictures for different modelling agents were juxtaposed and discussed.

Abstract: The object of the studies was A390.0 alloy (AlSi17Cu5Mg), similar to A3XX.X series, gravity cast into sand and metal moulds. This alloy is mainly used for cast pistons operating in I.C. engines, for cylinder blocks and housings of compressors, and for pumps and brakes. The A390.0 alloy was poured at temperatures 880 and 980°C, holding the melt for 30 minutes and casting from the temperature of 780°C. The assessment of the impact of the degree of overheating was to analysis the tensile strength. Studies were carried out on a normal-running fatigue testing machine, which was the mechanically driven resonant pulsator. For the needs of quantitative reliability evaluation and the time-to-failure evaluation, the procedures used in survival analysis, adapted to the analysis of failure-free operation with two-parametric Weibull distributions, were applied. Having determined the boundary value σ0 for Weibull distribution, the value of „m” modulus was computed along with other coefficients of material reliability, proposed formerly by the authors. Basing on the obtained results, a model of Weibull distribution function was developed for the tensile strength with respective graphic interpretation.

Abstract: The microstructure of Al processed by compression with oscillatory torsion (COT) method have been studied. This method was applied to refine the grain structure to ultrafine dimension. The aim of the study was to examine how severe plastic deformation technique (COT) - alter the microstructure. The second aim is to understand the mechanism of grain refinement. The microstructure was characterized using transmission electron microscopy (TEM) and scanning electron microscopy (SEM) equipped with electron back scattered diffraction (EBSD) facility.

Abstract: The results presented in this paper are concerned with the microstructure and the mechanical properties of the AlMg5 alloy subjected to severe plastic deformation by multiple compression in two orthogonal directions. Four experiments with an increasing number of passes were conducted on the Gleeble MAXStrain system in order to obtain various effective strain levels. The deformed microstructure was investigated by means of the light microscopy (LM) and the scanning transmission electron microscopy (STEM). The mechanical properties were determined for the most deformed, central parts of samples. Investigations revealed that severe cold deformation of the AlMg5 alloy leads to strong grain refinement. Moreover, fragmentation of large intermetallic inclusions and their regular distribution were obtained in the analysed, central parts of the samples. Microstructural changes led to significant improvement in the strength properties. After reaching the effective strain of 9, the AlMg5 alloy exhibited UTS, YS and HV values almost two times higher than corresponding values determined for the starting, annealed material.

Abstract: The article presents the course and the results of research on material and technological welding conditions of different aluminium alloys using standard (MIG-Pulse) and low energy welding method (CMT) as well as discusses the properties of welded joints and the application fields of modern low energy welding devices for joining thin aluminium sheets.

Abstract: Al₂O₃/AlSi12CuMgNi composites were fabricated using gas-pressure infiltration (T=700°C, p=4 MPa) of an aluminium alloy into alumina performs. Volume fraction of the ceramic phase was up to 30%, while the pore sizes of the ceramic preforms varied from 300 to 1000 µm. Ceramic preforms were formed by method of copying the cellular structure of the polymer matrix. The results of the X-ray tomography proved very good infiltration of the pores by the aluminium alloy. Residual porosity is approximately 1 vol%. Image analysis has been used to evaluate the specific surface fraction of the interphase boundaries (Sv). The presented results of the studies show the effect of the surface fraction of the interphase boundaries of ceramic-metal on the composite compressive strength, hardness and Young’s modulus. The composites microstructure was studied using scanning electron microscopy (SEM). SEM investigations proved that the pores are almost fully filled by the aluminium alloy. The obtained microstructure with percolation of ceramic and metal phases gives the composites high mechanical properties together with the ability to absorb the strain energy. Compression tests for the obtained composites were carried out and Young’s modulus was measured by the application of the DIC (Digital Image Correlation) method. Moreover, Brinell hardness tests were performed. Gas-pressure infiltration (GPI) allowed to fabricate composites with high compressive strength and stiffness.

Abstract: The paper presents the basics information about manufacturing and selected properties of composite with aluminium alloy matrix containing glassy carbon as a solid lubricant. The so far used method based on mixing the prepared glassy carbon particles with a liquid metal matrix, has been compared with a new method elaborated by the authors of the article. With this novel method carbon is introduced into a composite with the application of liquid carbon precursor and porous ceramic foams. It is then followed by precursor pyrolysis where, as the result, glassy carbon is obtained. Ceramic foams help liquid precursor penetrate the ceramic spheroid pores by forming a thin film of glassy carbon on their walls. The composite produced in such a way features uniform distribution of carbon within its entire volume which significantly improves tribological properties of the composite. Costly mixing procedure is not needed. Sliding friction coefficient of the new composite against cast iron (µ = 0.06-0.28 at wearing in and 0,12 after wearing in) is much lower than in case of composite containing only ceramic foam as a reinforcing phase (μ = 0.25-0.32).

Abstract: The today's interest in MMCp results from a number of their creative properties, which can be designed through a proper selection of reinforcing components and technological parameters. The composite machine elements such us engine, compressor parts obtained by casting methods require the specially final machining. The introduction of hard ceramic particles increase wear resistance of composite material compared to unreinforcement alloy. Simultaneously increase wear and reducing the durability of tools cutting. The presence of ceramic particles (SiC, Cs) in aluminium matrix influence on surface geometry formed in track of processing. In this paper the results of investigations of geometry surface of composite after machining will be presented. Applied machining conditions for composite material were the same as for unreinforcement alloy, it made possible to compare the conditions of machining processing. It the piston skirt was conducted light profilometry investigation were the parameters 2D and 3D surface topography evaluated. Results shows dependency of surface parameters (Ra, Rz) after machining on kind, size and volume fraction of reinforcement particles applied in composite material.