Solid State Phenomena Vol. 211

Abstract: The influence of strong overheating above T_liq. and modification with phosphorus in the form of CuP master alloy on the crystallisation process of AlSi17Cu5 alloy has been discussed. The study shows that with overheating of an alloy from the 3XX.X series above the melting point T_liq. (about 250÷300°C), the β phase undergoes practically complete dissolution. Then, in the liquid metal, areas with high variations in the content of the dissolved silicon appear. These are numerous microregions enriched with dissolved silicon, in which, due to overheating, partial formation of homogeneous nuclei takes place. This process is further enhanced with the use of a modifier (phosphorus) and, as a consequence of the modification process, additional "substrates" (AlP) arise in molten metal to serve as sites for the heterogeneous nucleation of primary Si crystals. In the vicinity of these microregions, some other sites with lower silicon content are formed, in which the proeutectic crystallisation of α (Al, Me) dendrites takes place. This is confirmed by the ATD thermal analysis diagrams, where the additional exothermic effect is observed after the nucleation and crystallisation of primary Si crystals and before the solidification of a α (Al) β (Si) eutectic.

Abstract: The paper presents the results of studies on the effect of the A390.0 (AlSi17Cu5) alloy overheating to a temperature of 920°C and modification with phosphorus (CuP10) on the resulting mechanical (HB, R_m, R_0.2) and plastic (A₅ and Z) properties. It has been shown that, so-called, "time-thermal treatment" (TTT) of an alloy in the liquid state, consisting in overheating the metal to about 250÷300°C above T_liq, holding at this temperature and rapid cooling, refines the structure and improves the mechanical properties. It has also been found that strong overheating of alloy above T_liq "enhances" the process of modification, resulting in the formation of fine-grain structure. The primary silicon crystals uniformly distributed in the eutectic and characteristics of the α (Al) solution supersaturated with alloying elements present in the starting alloy composition (Cu, Fe) provide not only an increase of strength at ambient temperature but also at elevated temperature (250°C), which is of particular importance for the automotive applications, especially as regards cast pistons operating in IC.

Abstract: Results of research on application of variable polarity MIG method for welding of thin sheets of 6082 and 5754 aluminium alloys have been presented. The influence of negative component portion in current and voltage course on process stability, joints quality and the microstructure evolution was discussed.

Abstract: This article presents the phisicochemical propreties of aluminium brings a lot of difficulties during soldering one of tchem is low melting point. The work also presents results of mechanical and metallographic investigations. Structural examination was performed by means of light microscopy and mechanical properties with the aim of shear strength test. On the basis structural investigation joints made with Zn and Zn with Ti addition indicated possibilities of reinforcement of soldered joint of aluminium

Abstract: The article presents the course and the results of research on material and technological welding conditions of 7xxx aluminium alloy using 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: The article presents the innovative MIG welding technology using variable polarity AC and reveals the results following the investigation of the impact of the EN ratio on the structure and HAZ width of overlay welds.

Abstract: In the presented work two methods of casting: gravity casting and centrifugal casting have been described. The main aim of the study was development procedures for producing the AlSi / SiC+C hybrid composite. Composite suspensions with the same phase composition were cast into molds with different coefficients of thermal conductivity. This allowed to determine the influence of thermal conditions on the formation of the structure and distribution of particles in the matrix. In the paper the conditions of casting, macro-and microstructure and selected properties of the casts have been presented. The structure of components and cast composites was examined by light and electron microscope, applying properly made preparations.

Abstract: In the production of composites by the suspension method (mechanical stirring) may beused, ceramic particles, which are wetted by the liquid metal such SiC, Al₂O₃ or glassy carbon.However, to obtain a stable suspension with the use a particle size below 10 μm is extremelydifficult. Phenomena related i.a. with agglomeration of particles, convection currents over moltenmetal surface make practically impossible to obtain composite material. One possibility to obtainfine reinforced composite is the use of in situ methods, in which the reinforcing phase is formed bythe reaction between the aluminum and the reactive powder oxides such FeO, TiO₂, SiO₂, NiO, Nb₂O₅ or Fe₂O₃. Such reactions are exothermic (aluminothermic) and their kinetics dependent onthe dispersion of the reactants, the quantitative phase composition and temperature.The technological solution involving the formation of a suspension with particles (chemically activewith aluminum) is one of the promising solutions to obtain batch material for the synthesis ofcomposites reinforced with Al₂O₃ and intermetallic phases. The aim of this study is to evaluate thesuitability of suspension technology to obtained in situ fine reinforced composite.

Abstract: Applying the metal forming for the production of machine parts from the composites in the aluminum alloy matrix will allow to widen the range of the practical appliances in this group of materials. In order to reach such results not only the reinforcement with ceramic particles into the matrix should be inserted but also the basic metal forming parameters of created composites must be set and verified. The article shows the results of plastometric research carried on the composites with PA31 alloy matrix. The research was conducted on the turning plastometer possessed by the Faculty of Mechanical Engineering of the Silesian Technology University. On the basis of the results the yielding curves were set in the system forming stress σ true deformation ε. Good coating in the PA31-SiC system causes limitation of the ability to deformation as a result of the separating boarder destruction and leads to destruction of the composite at the much lower deformation value and ductile stress. In case of the composites with glass carbon as well as in homofases system (PA31+15%WS) and heterofase (PA31+15%(SiC+WS)) the ductile stress value increase as follows 10 % and 20%.