Papers by Author: Jaroslaw Piątkowski

Abstract: The paper presents tests determining the influence of modification with phosphorus and fast cooling on the microstructure and friction coefficient of AlSi17Cu5Mg alloy. Changes mainly concern the size of primary silicon crystals and stereological parameters in reference to initial material. Modification with fast cooling was aimed at achievement of fine-crystalline structure with shapes of silicon crystals close to the spherical shape. The consequences of such activities are visible, significant changes in the tribological properties of tested alloy. Friction coefficient μ for material subject to fast cooling was on the level of 0.26 and for initial material it equalled 0.29.

Abstract: The article presents the surface coarseness analysis for alloy AlSi17Cu5Mg coupled with cast-iron EN-GJL-350. Material after friction was tested in pin-on-disk system with the use of tribological tester T-01. Such coupling is in accordance with parameters applied in combustion engines. Analysis of coarseness allows to determine the influence of technological history on the parameters of material wear. It is important due to the fact of the proper choice of technology for manufacturing the materials applied in pistons of combustion engines. Tests were conducted in accordance with norm PN-ISO 4288:1988.

Abstract: In the dissertation the influence of overheating of around 250^oC above T_liq on the material reliability of AlSi17Cu5 cast alloy has been shown. On the basis of static tensile test, the following had been determined: HB hardness, tensile strength and yield strength for four, chosen technological variants. The results were the base to verify the thesis of compliance between tested feature arrangement and normal arrangement, and on this ground also material reliability determined with Weibull’s statistic arrangement had been defined. This parameter grasp the interdependence between lasting probability and chosen material property of the alloy.

Abstract: In the dissertation the influence of overheating of around 250°C above T_liq and modification with phosphorus (CuP10 master alloy) on the microstructure of AlSi17Cu5 cast alloy has been shown. Substantial overheating above T_liq temperature of the alloy, causes complete dissolving of the β (Si) phase. In the liquid alloy, multiple areas are being created of different dissolved silicon content, where, as in the result of the overheating, the homogeneous nucleuses are being partially created. After modification with phosphorus, in liquid alloy, additional heterogenic nucleuses (AlP) of primary silicon crystals are being created. In the close neighborhood of these micro-areas, places depleted of silicon appears, where pre-eutectic α (Al, Me) dendrites crystallize.

Abstract: In the paper an effect of alloy modification, the mold material and the heat dissipation on the structure of hypereutectic silumin AlSi17 are presented. The investigated alloy was cast into: a ceramic (ATD), graphite and copper molds. In order to verify the conditions of heat dissipation through the mold, were used an additional cooling agents, such as water and liquid nitrogen. From the obtained ingots were prepared samples, which were stereological analyzed in the Metilo program.

Abstract: Studies were conducted on the kinetics and mechanism of oxidation of chromium-manganese steel under partial oxygen pressure p_O2 from 10^-11 to 10^-2 Pa at a temperature of 1173 K. The low oxygen partial pressure was produced in a gas mixture of CO-CO₂ and helium containing 0.2 ppm of oxygen. The kinetics of oxidation was examined by thermogravimetry using a thermobalance made by Setaram Company. Scale growth mechanism was determined with the use of markers. The oxidation products were analyzed by scanning electron microscopy (SEM, EDS). It was found that at low partial pressure of oxygen, MnO oxide was forming on the steel surface. From an analysis of the curves of the steel weight growth per unit surface in function of time it followed that the oxidation assumed a parabolic course. A relationship has been determined between the coefficient of self-diffusion of manganese in MnO and the oxygen partial pressure.

Abstract: The article describes the process of crystallization of an AlSi17Cu5 (the A3XX.X series according to ASTM standard) alloy which has been modified with 0.05 wt. % P (CuP10 master alloy) and overheated to a temperature of 920°C. It has been shown that, so-called, "time-temperature treatment" (TTT) of alloy in the liquid state, which consists in overheating the alloy to a temperature above T_liq (about 250-300°C), holding at this temperature and rapid cooling, alters the morphology of primary silicon crystals. By the ATD method of thermal analysis, the characteristic temperature of crystallization (T_liq., T_Emin., T_Emax., T_E(Cu), T_E(Fe), T_sol.) were determined, and exothermic effects of the modifier and high-degree overheating on the crystallization course of the investigated alloy were examined. A new mechanism of proeutectic crystallization of the a(Al, Me=Cu, Fe) dendrites was proposed. The course of this process is dynamic enough to promote, due to local undercooling, the evolution of heat, which in the ATD curve appears as a well visible additional exothermic effect designated as T_X. It is due to the presence in the liquid alloy of microregions with varied content of dissolved silicon.

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: 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: Production of primary Al- alloys belong to heavy source fouling of life environs. Care of environment in industry of aluminium connects with the decreasing consumptions resource as energy, materials, water and soil, with increase recycling and extension life of products. Recycled (secondary) aluminium alloys are made out of Al-scrap and workable Al-garbage by recycling. Applications of these alloys in recent years increase especially in automotive industry (dynamic exposed cast, engine parts, cylinder heads, pistons and so on). Controlling the microstructure of secondary aluminium cast alloy is very important, because these alloy containing more of additions elements, that forming various intermetallic phases in the structure. Improved mechanical properties of secondary alloys are strongly dependent upon the morphologies, type and distribution of the second phases, which are in turn a function of alloy composition and cooling rate. The presence of additional elements as Mg, Mn, Fe or Cu allows many complex intermetallic phases to form, which make characterization non-trivial. A combination of different analytical techniques (light microscopy, scanning electron microscopy (SEM) upon deep etching and energy dispersive X-ray analysis (EDX)) were therefore been used for the various phases identification.