Papers by Keyword: Overheating Degree

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: 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: The paper presents the results of microscopic examinations of the growth of primary silicon crystals in hypereutectic A390.0 (AlSi17Cu5Mg) silumin. A diagram of the growth of primary silicon crystals in the melt without overheating and superheated to a temperature of 920°C has been presented. From the experimental results obtained on crystal morphologies of primary silicon, different sequences of crystal growth of the primary silicon can be expected. In the silumin without overheating, five-pointed star-shaped particles form, after superheating, the crystals of primary silicon take more compact shapes. This structure provides better mechanical properties and thus increases the area of application of alloys with hypereutectic silicon content.

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 effect of overheating on the solidification process and microstructure evolution in AlSi17 silumin was discussed. The alloy melt was held for 40 minutes at 780, 860, 940 and 1020oC, and then cast at a temperature of 780oC to standard ceramic probe. Characteristic parameters of the AlSi17 alloy solidification process, especially Tliq, TE, Tsol, were determined. Examinations of microstructure were also carried out, showing that the higher was the overheating temperature, the higher was the degree of the primary silicon crystals refinement.