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M. Łągiewka

Abstract

The paper constitutes the culmination of the foregoing investigations concerning the influence of short carbon fibre on the enhancement of AlMg10 alloy properties. The presented work brings forward the results of examinations of mechanical and tribological properties of metal matrix composites (MMCs) based on this alloy. Composites were produced by two methods: either by gravity casting or by squeeze casting in semi-solid state of a composite suspension previously obtained through mixing of its components. The volume fraction of the reinforcing phase varied and took the value of 5, or 10, or finally 15 vol. %. Specimens cut out of the experimental castings were examined with respect both to their mechanical properties, i.e. the tensile strength and unit elongation, and to their tribological behaviour. A series of examinations of the mechanical properties proved a slight increase in tensile strength and a minor decrease in unit elongation of the examined composite materials both for gravity cast and squeeze cast specimens, as compared with the properties of pure matrix alloy. The introduction of short carbon fibre into the matrix alloy resulted also in the increased abrasive wear resistance of the examined composites in comparison to the non-reinforced matrix.

Open access

M. Łągiewka and Z. Konopka

The Influence of Material of Mould and Modification on the Structure of Alsi11 Alloy

The presented work discusses the influence of material of foundry mould on the effect of modification of AlSi11 alloy. For this purpose castings were produced in moulds made of four various materials. Castings of the first type were cast in a metal die, the second ones in the conventional mould of bentonite-bound sand, those of the third type in the sand mould with oil binder, the last ones in a shell mould where phenol-formaldehyde resin was applied as a binder. All the castings were made of AlSi11 alloy modified with strontium. For a purpose of comparison also castings made of the non-modified alloy were produced. The castings were examined with regard to their microstructures. The performed investigations point out that the addition of strontium master alloy results in refining of the alloy structure, particularly of the α-phase, causes some morphological changes in the alloy and the refinement of eutectics. The advantageous influence of modifier on the structure of the examined silumin was observed particularly in the case of alloy cast either in the conventional oil-bound sand mould or in the shell mould. The non-modified alloy cast into a metal die exhibits a structure similar to those of modified alloy solidifying in the other moulds. The improvement in both tensile strength and unit elongation suggests that the modification was carried out correctly. The best mechanical properties were found for the alloy cast in a metal die, both with and without modification treatment.

Open access

M. Łągiewka

Abstract

The paper is a review of the previous investigations concerning the influence of graphite particles both on the casting properties of metal matrix composites (MMCs). The work presents the examination results of casting properties (i.e. castability and shrinkage) of the MMCs with matrices of a selected aluminium alloy reinforced with graphite particles. There is also presented the influence of graphite particles on the surface tension and viscosity of the flowing and filling the mould composite suspension. The suspensions containing various percentages of graphite particles (namely 5%, 10%, or 15% in volume) were prepared in order to perform the above mentioned examinations. Castability (fluidity) of these suspensions was measured in two ways, i.e. by means of both the spiral test and the rod test, while their shrinkage was determined with the use of a device designed and assembled in the Department of Foundry Engineering, CUT. The device enables to determine changes in the length of a casting during its solidification with respect to the specified length of the test rod. The surface tension was determined by the wedge casting method consisting in the pouring of metal into an open shell mould with the cavity of wedge geometry, the sharp edge being perpendicular to the free metal surface. The change in viscosity corresponding to the change in graphite particles percentage was calculated from Einstein’s equation. The results of examinations show that the introduction of reinforcing graphite particles results in both a significant increase in the viscosity of the flowing suspension and a considerable decrease in its castability. The greater dimensional stability of castings was observed, i.e. the shrinkage of composite castings was smaller than the shrinkage of matrix alloy itself. An increase in surface tension index value with an increase in volume percentage of graphite particles in composite was also noticed.

Open access

Z. Konopka, M. Łągiewka, M. Nadolski and A. Zyska

Abstract

The purpose of the work is the determination of the strengthening coefficient for the AlSi13Cu2 alloy matrix composite reinforced with chopped carbon fibre and produced by high-pressure casting method. This coefficient was determined during the static tensile test using the Ramberg-Osgood equation. The regression relationships between strain and stress were established, serving as a basis for finding the strengthening coefficient values. The measurements and calculations were performed also for the matrix alloy itself, for the purpose of comparison. The examined coefficient decreased with an increase of fibre fraction in the composite. Its value for composite containing 15 vol. % of chopped fibre was found to be lower by 30% than the value determined for matrix alloy, what means the strengthening of the alloy to such a degree.

Open access

M. Łągiewka and Z. Konopka

Abstract

The presented work describes the results of examination of the mechanical properties of castings made either of AlSi9Mg alloy matrix composite reinforced with short carbon fibre or of the pure AlSi9Mg alloy. The tensile strength, the yield strength, Young’s modulus, and the unit elongation were examined both for initial castings and for castings made of the remelted composite or AlSi9Mg alloy. After preparing metallographic specimens, the structure of the remelted materials was assessed. A few non-metallic inclusions were observed in the structure of the remelted composite, not occurring in the initial castings. Mechanical testing revealed that all the examined properties of the initial composite material exceed those of the non-reinforced matrix. A decrease in mechanical properties was stated both for the metal matrix and for the composite after the remelting process, but this decrease was so slight that it either does not preclude them from further use or does not restrict the range of their application.

Open access

M. Łągiewka and Z. Konopka

Abstract

The presented work deals with the influence of the addition of soft graphite particles on the abrasive wear of composite reinforced with hard SiC particles. The discussed hybrid composites were produced by stirring the liquid alloy and simultaneous adding the mixture of particles. The adequately prepared suspension was gravity cast into a metal die. Both the composite castings obtained in this way and the comparative castings produced of the pure matrix alloy were examined for the abrasive wear behaviour. Photomacrographs of the sliding surfaces of the examined composites were taken, and also the hardness measurements were carried out. It was found that even a small addition of Cgr particles influences positively the tribological properties of the examined composite materials, protecting the abraded surface from the destructive action of silicon carbide particles. The work presents also the results of hardness measurements which confirm that the composite material hardness increases with an increase in the volume fraction of hard reinforcing particles.

Open access

Z. Konopka, A. Pasieka, M. Łągiewka, M. Nadolski and A. Zyska

Abstract

The work presents the investigation results concerning the structure of composite pressure die castings with AlSi11 alloy matrix reinforced with SiC particles. Examination has been held for composites containing 10 and 20 volume percent of SiC particles. The arrangement of the reinforcing particles within the matrix has been qualitatively assessed in specimens cut out of the castings. The index of distribution was determined on the basis of particle count in elementary measuring fields. The tensile strength, the yield point and elongation of the obtained composite were measured. Composite castings were produced at various values of the piston velocity in the second stage of injection, diverse intensification pressure values, and various injection gate width values. The regression equation describing the change of the considered arrangement particles index and mechanical properties were found as a function of the pressure die casting parameters. The infuence of particle arrangement in composite matrix on mechanical properties these material was examined and the functions of correlations between values were obtained. The conclusion gives the analysis and the interpretation of the obtained results.

Open access

M. Łągiewka, Z. Konopka, A. Zyska and M. Nadolski

Abstract

The possibility of controlling the solidification and cooling time of castings creates prospects of improving their structure and by the same their properties. Thermal properties of the mould constitute therefore an important factor which is necessary to consider while seeking for the mentioned improvement. The presented work illustrates the method of determining some basic thermal coefficients of moulding material, i.e. the coefficient of temperature equalisation a2, known also as the temperature diffusivity, and the heat accumulation coefficient b2, which characterises the ability of moulding material to draw away the heat from a casting. The method consists in experimental determining the temperature field within the mould during the processes of pouring, solidification and cooling of the casting. The performed measurements allow for convenient and exact calculations of the sought-after coefficients. Examinations were performed for the oil bonded moulding sand of trade name OBB SAND ‘E’. The experiment showed that the obtained value of b2 coefficient differs from the value calculated on the basis of theoretical considerations available in publications. Therefore it can be stated that theoretical calculations of the heat accumulation coefficient are thus far not sufficient and not quite reliable, so that these calculations should be verified experimentally.

Open access

M. Nadolski, Z. Konopka, M. Łągiewka and A. Zyska

Abstract

The work deals with the influence of change in the filling conditions of the ceramic moulds with plaster binder on the presence of gaseous porosity and the microstructure of the achieved test castings with graded wall thickness. Castings made of EN AC-44000 alloy, produced either by gravity casting, or by gravity casting with negative pressure generated around the mould (according to the Vacumetal technology), or by counter-gravity casting were compared. The results of examinations concerning the density of the produced castings indicate that no significant change in porosity was found. The increased size of silicon crystals was found for the increased wall thicknesses due to the slower cooling and solidification of castings.

Open access

A. Zyska, Z. Konopka, M. Łągiewka and M. Nadolski

Abstract

The paper presents the results of investigations concerning the influence of negative (relative) pressure in the die cavity of high pressure die casting machine on the porosity of castings made of AlSi9Cu3 alloy. Examinations were carried out for the VertaCast cold chamber vertical pressure die casting machine equipped with a vacuum system. Experiments were performed for three values of the applied gauge pressure: -0.3 bar, -0.5 bar, and -0.7 bar, at constant values of other technological parameters, selected during the formerly carried initial experiments. Porosity of castings was assessed on the basis of microstructure observation and the density measurements performed by the method of hydrostatic weighing. The performed investigation allowed to find out that - for the examined pressure range - the porosity of castings decreases linearly with an increase in the absolute value of negative pressure applied to the die cavity. The negative pressure value of -0.7 bar allows to produce castings exhibiting porosity value less than 1%. Large blowholes arisen probably by occlusion of gaseous phase during the injection of metal into the die cavity, were found in castings produced at the negative pressure value of -0.3 bar. These blowholes are placed mostly in regions of local thermal centres and often accompanied by the discontinuities in the form of interdendritic shrinkage micro-porosity. It was concluded that the high quality AlSi9Cu3 alloy castings able to work in elevated temperatures can be achieved for the absolute value of the negative pressure applied to the die cavity greater than 0.5 bar at the applied set of other parameters of pressure die casting machine work.