Constructional materials as Al - alloys can be replaced by other materials with high strength to low mass density ratio, e.g. Mg-alloys. In order to pre-casting of holes and cavities cores based on pure inorganic salt can be applied due to easy cleaning of even geometrically complex pre-cast holes. This technology is applied mainly for gravity and low-pressure casting technology. This contribution is aimed at studying of mutual interaction of the Mg-alloy and the salt core. Experiments were focused on surface quality; macro- and microstructure of testing casting samples determination. Metallographic analysis and scanning electron microscope (SEM) with X-ray energy-dispersion superficial and spot microanalysis (EDAX) were employed

J. Beňo

M. Morys

P. Lackova

P. Lichý

Hrčak - Portal of scientific journals of Croatia

303METALURGIJA 53 (2014) 3, 303-306P. LICHÝ, J. BEŇO, P. LACKOVA, M. MORYSINFLUENCE OF ECOLOGICALLY FRIENDLY CORES ON SURFACE QUALITY OF CASTINGS BASED ON MAGNESIUM ALLOYSReceived – Prispjelo: 2013-06-21Accepted – Prihvaćeno: 2013-11-30Original Scientific Paper – Izvorni znanstveni radISSN 0543-5846METABK 53(3) 303-306 (2014)UDC – UDK 669.721:620.18:669.163=111P. Lichý, J. Beňo, VSB-TU Ostrava, FMME, Ostrava, Czech Repub-lic, P. Lackova, Technical University of Košice, Slovakia, M. Morys, Faculty of Mechanical Engineering, Silesian University of Technology, PolandConstructional materials as Al - alloys can be replaced by other materials with high strength to low mass density ratio, e.g. Mg-alloys. In order to pre-casting of holes and cavities cores based on pure inorganic salt can be applied due to easy cleaning of even geometrically complex pre-cast holes. This technology is applied mainly for gravity and low-pressure casting technology. This contribution is aimed at studying of mutual interaction of the Mg-alloy and the salt core. Experiments were focused on surface quality; macro- and microstructure of testing casting samples determination. Metallographic analysis and scanning electron microscope (SEM) with X-ray energy-dispersion su-perficial and spot microanalysis (EDAX) were employed.Key words: magnesium alloys, microstructure, salt cores, castingsINTRODUCTIONOptimal ratio of high specific strengths and low mass density predetermine the magnesium alloys for their utilization in the field of constructional materials especially in the aircraft, automobile [1] and rocket in-dustry but in manufacture of optical and instrumental technique, in textile and consumer goods industry too. Mg-alloys also show good castability and weldability under controlled atmosphere and better machinability than Al-alloys. Disadvantages of Mg-alloys consist in steep decrease of mechanical properties under increased temperatures (above 120 °C) [2], low creep resistance caused by increasing volume amount of Al, low elastic modulus, high degree of shrinkage during solidification and low corrosion resistance in some applications [3]. These properties are decisive for using of castings from these alloys for thermally stressed parts in car design – e.g. engine blocks and cylinder heads. Thus among these applications [4, 5] all the time predominate the castings from aluminium alloys or Mg-alloys alloyed with rare earth metals higher resistant to increased tem-peratures.In spite of attractive properties the casting of Mg-alloys is connected with a number of problems as a re-sult of high affinity of magnesium to oxygen. For that reason it is necessary during casting to use special addi-tives – inhibitors (fluorides, H3BO3, additives based on urea or sulphur) that protect the melt flow from oxida-tion with no negative influence on magnesium alloy quality. Casting in metal moulds – pressure, low-pres-sure, and partly gravity casting – are predominant man-ufacturing technologies of magnesium alloys castings. For pre-casting of less complicated holes the metal cores can be used. At present the core mixtures based on organic binders are ousted and replaced with inorganic binders that have the same utility properties (primary strengths of cores, optimal shelf life, surface quality of pre-cast holes etc.) and they are not too environmentally straining. Those criteria are also met by cores based on inorganic salts manufactured either by high-pressure squeezing of crystalline salts, injecting of the salt melt [6], or the use of salt solutions [7-9]. Cores can be man-ufactured in a closed ecological cycle. In addition to it during casting, cooling, and solidification of castings the salt cores don’t emit any VOCs emissions. Proper-ties of salt cores can be further on modified and opti-mized for individual casting processes by changing the preparation conditions (intensity of squeezing pres-sures, shooting temperature etc.), by composition of the base matrix (kind of salt, of the additive). This contribu-tion is aimed at study of mutual interaction of salt cores with surface of the casting from chosen Mg-alloys. MATERIALS AND METHODSMagnesium alloy AZ91 was (of chemical composi-tion 9 % Al; and up to 1 % Zn;) casted in the bentonite bonded moulding mixture of composition 91 % SiO2 ŠH35Š, 4,5 % North Bohemia bentonite activated with soda and 5 % of inhibitor based on sulphur of moisture corresponding to compactibility of 46 ± 2 % was chosen for experiments [10]. Magnesium alloys were molten in a steel crucible in an electric resistance furnace. The 304  METALURGIJA 53 (2014) 3, 303-306P. LICHÝ et al.: INFLUENCE OF ECOLOGICALLY FRIENDLY CORES ON SURFACE QUALITY OF CASTINGS BASED...molten metal protection was provided by a covering and refining preparation EMGESAL.Salt cores based on chemically pure salt (chloride) and the same salt with two different additives (marked A and B) that on the one hand improve surface quality of the casting from the core side and on the other one they increase mechanical strengths and heat resistance of the cores were used as test cores. The cores were pre-pared by high-pressure squeezing (100 and 200 kN; marking 1 and 2) from z gently moistened salt matrix. The cores are strengthened as a result of mechanical de-formation of grains (conglomeration) and recrystalliza-tion along the grain boundaries. With the aim of determining the influence of casting temperature on surface quality of Mg-alloys the test castings with salt cores were cast under two casting temperatures (700 and 800 °C) in oxidation atmosphere under constant thermal load of the mould (weight ratio of mould: metal 9,3:1). Surface quality of the casting from the core side was determined with the aid of verti-cal (amplitude) roughness – mean arithmetic roughness Ra [µm] as a mean value from ten measurements of roughness of the given sample surface. A digital roughness meter SurfTest SJ-301-Mitutoyo was used for measurements of mean arithmetic rough-ness RA (according to the ISO 1997 standard). With re-gard to microstructure the prepared samples were ex-amined on a scanning electron microscope (SEM) with X-ray energy-dispersion superficial and spot microa-nalysis (EDAX).RESULTS AND DISCUSSIONSurface quality of the test castings in the framework of the experiment was evaluated with use of cores of different composition (chemically pure salt; the same salt with 15 % of an additive) with the aid of mean arith-metic roughness RA as a mean value from ten measure-ments on the total casting surface from the core side and with the aid of a stereomicroscope (Table 1). The Table gives the numerical marking of samples xy where for x = 1;2 the casting temperature is 800 °C and x = 3;4 the casting temperature is 700 °C. For y = 1 the additive A was used; y = 2 with no additive; y = 3 the additive B. From obtained results of surface quality of castings from the core side evaluated in as cast state the high surface quality is evident. Surface roughness ranged within 5,91 and 26,31 µm (Figure 1 – 5,91 µm; Fig-ure 2 -26,31 µm). Positive effect of additives was evi-dent; their presence improved the smoothness of the casting surface. This assumption has been proved by the lowest value of mean arithmetic roughness (5,91 µm) determined for the additive A prepared with maximum pressing power (200 kN). It is generally valid that with growing pressing pow-er the core porosity is decreasing what decreases a pos-sibility of metal penetration with resulting in a smother final surface of the casting. In case of combining the salt cores for magnesium alloys it is highly necessary to care about good degassing of the mould for the reason of huge gas generation mainly during casting resulting in a number of surface and internal casting defects.Metallographic analysis of the casting surface layerWith regard to results obtained from evaluation of surface quality of test castings a sample giving the high-est surface quality (sample 41, RA = 5,91 µm) was chosen for metallographic analysis and it was compared with the sample 21 prepared by the same way. For preparation of these samples the cores with the additive A were pre-pared, squeezed with higher pressing power (200 kN) and the samples were cast under casting temperature of 700 °C (sample 41) and 800 °C (sample 21). Microstruc-Table 1 Mean arithmetic roughness of testing cast samplesSample 11 12 13 21 22 23 31 32 33 41 42 43RA /µm 8,43 14,46 8,57 17,54 26,31 12,40 25,63 18,94 16,51 5,91 21,5 14,88Figure 1 Surface quality of test sample 22Figure 2 Surface quality of test sample 41305METALURGIJA 53 (2014) 3, 303-306P. LICHÝ et al.: INFLUENCE OF ECOLOGICALLY FRIENDLY CORES ON SURFACE QUALITY OF CASTINGS BASED...ture of the surface part of test castings is shown on Figure 3 (sample 21) and Figure 4 (sample 41).From the point of view of microstructure of the AZ91 alloy it is possible to observe considerable influence of casting temperature. Samples cast under lower casting temperature (700 °C; Figure 4) have considerably more fine-grained structure and higher mechanical properties of the cast material can be expected in this case. Higher material homogeneity in the total studied sample volume without conspicuous differences be-tween the superficial and internal casting part is percep-tible in this sample.Samples of castings prepared under higher casting temperature (800 °C; Figure 3) show considerably low-er homogeneity degree and considerable differences be-tween the peripheral and central part of the test sample can be found. Increased inhomogeneity of studied sam-ples can be further on augmented by the salt matrix de-composition (770 °C) accompanied with considerable generation of gaseous Cl2.Evaluation of microstructure with the aid of SEM and EDAX analysesSamples of the material that was in contact with salt cores prepared from pure salt matrix only (without ad-ditives) and squeezed with higher pressing power (200 kN), i.e. the sample 42, were chosen for this part of the experiment only.The used additives are inorganically based only with decomposition temperature considerably exceeding ex-perimental temperatures achieved during casting, so-lidification, and cooling of castings and thus it can be expected that they will have no influence on the base metal matrix. Microstructures of studied samples were evaluated from different points of measurement (Figure 5) of both the base metal matrix and other structural constituents, and the present porosity for identification of the kind of formed defects. Analyzed chemical com-position of studied samples is given in Table 2.From resulting values of EDAX analysis it is possi-ble to identify internal defects of the cast material. Gas-eous products of thermal destruction of both the salt matrix of the core itself, and the inhibitor present in the bentonite bonded moulding mixture participate in de-fects formation (Table 2). Increased concentration of chlorine and sulphur was primarily determined espe-cially in points corresponding to points of measure-ments Spectrum 4 ; 7 and 11 of the studied sample.CONCLUSIONThis contribution was aimed at checking the use of cores based on inorganic salts for casting of magnesium Table 2 Results of EDAX analysis of sample 42Name Elements/ weight %O Na Mg Al Si Mn Zn S Cl K CaSpectrum1 1,34 42,12 0,65 55,89Spectrum2 59,27 37,49 3,24Spectrum3 94,51 5,49Spectrum4 61,77 32,24 3,68 1,06 1,25Spectrum5 54,41 43,86 0,97 0,32 0,43Spectrum6 65,12 26,19 7,20 1,00 0,33 0,16Spectrum7 22,81 0,24 3,31 2,91 0,89 2,08 0,48 1,77 0,62Spectrum8 38,81 11,25 9,05 1,69 0,36 0,13 2,38Spectrum9 56,14 41,98 0,27 0,23 0,28 1,10Spectrum10 52,79 45,75 1,03 0,11 0,31Spectrum11 62,29 31,75 4,33 1,20 0,42Figure 3 Detail of surface of sample 21Figure 4 Detail of surface of sample 41306  METALURGIJA 53 (2014) 3, 303-306P. LICHÝ et al.: INFLUENCE OF ECOLOGICALLY FRIENDLY CORES ON SURFACE QUALITY OF CASTINGS BASED...alloys. The application of salt cores for pre-casting of cavities and holes for gravity and low-pressure cast cast-ings from Mg-alloys is not known in common practice.From the point of view of chemical basis of used moulds, cores and the inhibitor, chemical processes run-ning during casting and cooling of the casting, it is nec-essary to ensure a sufficient exhausting of gases from the mould cavity for ensuring high casting quality. In case of cores used in this experiment an increased oc-currence of internal defects of cast samples has been confirmed. It was caused by interaction of generating gas with the base metal matrix. One of possibilities of achieving higher quality of cast parts is the application of spirituous preservative coatings or the use of cores with different base salt matrix.AcknowledgementThis work was elaborated within the frame of the research project TA02011333 (Technology Agency of the CR).REFERENCES[1] K. Rusín: Slévárenství, 63 (2013) 7/8, 236-238.[2] P. Lichý, J. Beňo, M. Cagala, J. Hampl: Metalurgija, 52 (2013) 4, 473-476.[3] J. Przondziono, W. Walke, A. Szuła, E. Hadasik, J. Szala, J. Wieczorek: Metalurgija, 50 (2011) 4, 239-243.[4] D. Vojtĕch: Metalurgija, 49 (2010) 3, 181-185.[5] M. Holtzer; R. Dańko; S. Żymankowska-Kumon: Metalur-gija, 51 (2012) 3, 337-340.[6] P. Jelínek; E. Adámková; J. Beňo; F. Mikšovský, V. Bry-ksí; M. Ficková: Technológ, 5 (2013) 2, 17-22.[7] H. Hänsel: Giesserei, 89 (2002) 2, 74-76.[8] M. Faller; A. Mössner: Giesserei, 96 (2009) 9, 72-74.[9] S. Dobosz; P. Jelínek; K. Major-Gabryś: China Foundry, 8 (2011) 4, 438-446.[10] S. Roskosz, J. Adamiec, M. Błotnicki: Archives of Foundry Engineering, 7 (2007) 1, 143-146.Note:  The responsible translator for English language is František Urbánek, Brno, Czech Republic5a Magnification 400x 5b Magnification 150x 5c Magnification 400xFigure 5 Details of microstructure of sample 42 with different extension

Influence of ecologically friendly cores on surface quality of castings based on magnesium alloys

Constructional materials as Al - alloys can be replaced by other materials with high strength to low mass density
ratio, e.g. Mg-alloys. In order to pre-casting of holes and cavities cores based on pure inorganic salt can be applied
due to easy cleaning of even geometrically complex pre-cast holes. This technology is applied mainly for gravity and
low-pressure casting technology. This contribution is aimed at studying of mutual interaction of the Mg-alloy and
the salt core. Experiments were focused on surface quality; macro- and microstructure of testing casting samples
determination. Metallographic analysis and scanning electron microscope (SEM) with X-ray energy-dispersion superficial
and spot microanalysis (EDAX) were employed.Web of Science53330630

Lichý, Petr

Beňo, Jaroslav

Lacková, Petra

Morys, Marcin

DSpace at VSB Technical University of Ostrava

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303 METALURGIJA 53 (2014) 3, 303-306P. LICHÝ, J. BEŇO, P. LACKOVA, M. MORYSINFLUENCE OF ECOLOGICALLY FRIENDLY CORES ON SURFACE QUALITY OF CASTINGS BASED ON MAGNESIUM ALLOYSReceived – Prispjelo: 2013-06-21Accepted – Prihvaćeno: 2013-11-30Original Scientific Paper – Izvorni znanstveni radISSN 0543-5846METABK 53(3) 303-306 (2014)UDC – UDK 669.721:620.18:669.163=111P . Lichý, J. Beňo, VSB-TU Ostrava, FMME, Ostrava, Czech Repub-lic, P. Lackova, Technical University of Košice, Slovakia, M. Morys, Faculty of Mechanical Engineering, Silesian University of Technology, PolandConstructional materials as Al - alloys can be replaced by other materials with high strength to low mass density ratio, e.g. Mg-alloys. In order to pre-casting of holes and cavities cores based on pure inorganic salt can be applied due to easy cleaning of even geometrically complex pre-cast holes. This technology is applied mainly for gravity and low-pressure casting technology. This contribution is aimed at studying of mutual interaction of the Mg-alloy and the salt core. Experiments were focused on surface quality; macro- and microstructure of testing casting samples determination. Metallographic analysis and scanning electron microscope (SEM) with X-ray energy-dispersion su-perficial and spot microanalysis (EDAX) were employed.Key words: magnesium alloys, microstructure, salt cores, castingsINTRODUCTIONOptimal ratio of high specific strengths and low mass density predetermine the magnesium alloys for their utilization in the field of constructional materials especially in the aircraft, automobile [1] and rocket in-dustry but in manufacture of optical and instrumental technique, in textile and consumer goods industry too. Mg-alloys also show good castability and weldability under controlled atmosphere and better machinability than Al-alloys. Disadvantages of Mg-alloys consist in steep decrease of mechanical properties under increased temperatures (above 120 °C) [2], low creep resistance   caused by increasing volume amount of Al, low elastic modulus, high degree of shrinkage during solidification and low corrosion resistance in some applications [3]. These properties are decisive for using of castings from these alloys for thermally stressed parts in car design – e.g. engine blocks and cylinder heads. Thus among these applications [4, 5] all the time predominate the castings from aluminium alloys or Mg-alloys alloyed with rare earth metals higher resistant to increased tem-peratures.In spite of attractive properties the casting of Mg-alloys is connected with a number of problems as a re-sult of high affinity of magnesium to oxygen. For that reason it is necessary during casting to use special addi-tives – inhibitors (fluorides, H3BO3, additives based on urea or sulphur) that protect the melt flow from oxida-tion with no negative influence on magnesium alloy quality. Casting in metal moulds – pressure, low-pres-sure, and partly gravity casting – are predominant man-ufacturing technologies of magnesium alloys castings. For pre-casting of less complicated holes the metal cores can be used. At present the core mixtures based on organic binders are ousted and replaced with inorganic binders that have the same utility properties (primary strengths of cores, optimal shelf life, surface quality of pre-cast holes etc.) and they are not too environmentally straining. Those criteria are also met by cores based on inorganic salts manufactured either by high-pressure squeezing of crystalline salts, injecting of the salt melt [6], or the use of salt solutions [7-9]. Cores can be man-ufactured in a closed ecological cycle. In addition to it during casting, cooling, and solidification of castings the salt cores don’t emit any VOCs emissions. Proper-ties of salt cores can be further on modified and opti-mized for individual casting processes by changing the preparation conditions (intensity of squeezing pres-sures, shooting temperature etc.), by composition of the base matrix (kind of salt, of the additive). This contribu-tion is aimed at study of mutual interaction of salt cores with surface of the casting from chosen Mg-alloys. MATERIALS AND METHODSMagnesium alloy AZ91 was (of chemical composi-tion 9 % Al; and up to 1 % Zn;) casted in the bentonite bonded moulding mixture of composition 91 % SiO2 ŠH35Š, 4,5 % North Bohemia bentonite activated with soda and 5 % of inhibitor based on sulphur of moisture corresponding to compactibility of 46 ± 2 % was chosen for experiments [10]. Magnesium alloys were molten in a steel crucible in an electric resistance furnace. The 304   METALURGIJA 53 (2014) 3, 303-306P. LICHÝ et al.: INFLUENCE OF ECOLOGICALLY FRIENDLY CORES ON SURFACE QUALITY OF CASTINGS BASED...molten metal protection was provided by a covering and refining preparation EMGESAL.Salt cores based on chemically pure salt (chloride) and the same salt with two different additives (marked A and B) that on the one hand improve surface quality of the casting from the core side and on the other one they increase mechanical strengths and heat resistance of the cores were used as test cores. The cores were pre-pared by high-pressure squeezing (100 and 200 kN; marking 1 and 2) from z gently moistened salt matrix. The cores are strengthened as a result of mechanical de-formation of grains (conglomeration) and recrystalliza-tion along the grain boundaries. With the aim of determining the influence of casting temperature on surface quality of Mg-alloys the test castings with salt cores were cast under two casting temperatures (700 and 800 °C) in oxidation atmosphere under constant thermal load of the mould (weight ratio of mould: metal 9,3:1). Surface quality of the casting from the core side was determined with the aid of verti-cal (amplitude) roughness – mean arithmetic roughness Ra [µm] as a mean value from ten measurements of roughness of the given sample surface. A digital roughness meter SurfTest SJ-301-Mitutoyo was used for measurements of mean arithmetic rough-ness RA (according to the ISO 1997 standard). With re-gard to microstructure the prepared samples were ex-amined on a scanning electron microscope (SEM) with X-ray energy-dispersion superficial and spot microa-nalysis (EDAX).RESULTS AND DISCUSSIONSurface quality of the test castings in the framework of the experiment was evaluated with use of cores of different composition (chemically pure salt; the same salt with 15 % of an additive) with the aid of mean arith-metic roughness RA as a mean value from ten measure-ments on the total casting surface from the core side and with the aid of a stereomicroscope (Table 1). The Table gives the numerical marking of samples xy where for x = 1;2 the casting temperature is 800 °C and x = 3;4 the casting temperature is 700 °C. For y = 1 the additive A was used; y = 2 with no additive; y = 3 the additive B. From obtained results of surface quality of castings from the core side evaluated in as cast state the high surface quality is evident. Surface roughness ranged within 5,91 and 26,31 µm (Figure 1 – 5,91 µm; Fig-ure 2 -26,31 µm). Positive effect of additives was evi-dent; their presence improved the smoothness of the casting surface. This assumption has been proved by the lowest value of mean arithmetic roughness (5,91 µm) determined for the additive A prepared with maximum pressing power (200 kN). It is generally valid that with growing pressing pow-er the core porosity is decreasing what decreases a pos-sibility of metal penetration with resulting in a smother final surface of the casting. In case of combining the salt cores for magnesium alloys it is highly necessary to care about good degassing of the mould for the reason of huge gas generation mainly during casting resulting in a number of surface and internal casting defects.Metallographic analysis of the casting surface layerWith regard to results obtained from evaluation of surface quality of test castings a sample giving the high-est surface quality (sample 41, RA = 5,91 µm) was chosen for metallographic analysis and it was compared with the sample 21 prepared by the same way. For preparation of these samples the cores with the additive A were pre-pared, squeezed with higher pressing power (200 kN) and the samples were cast under casting temperature of 700 °C (sample 41) and 800 °C (sample 21). Microstruc-Table 1 Mean arithmetic roughness of testing cast samplesSample 11 12 13 21 22 23 31 32 33 41 42 43RA /µm 8,43 14,46 8,57 17,54 26,31 12,40 25,63 18,94 16,51 5,91 21,5 14,88Figure 1 Surface quality of test sample 22Figure 2 Surface quality of test sample 41305 METALURGIJA 53 (2014) 3, 303-306P. LICHÝ et al.: INFLUENCE OF ECOLOGICALLY FRIENDLY CORES ON SURFACE QUALITY OF CASTINGS BASED...ture of the surface part of test castings is shown on Figure 3 (sample 21) and Figure 4 (sample 41).From the point of view of microstructure of the AZ91 alloy it is possible to observe considerable influence of casting temperature. Samples cast under lower casting temperature (700 °C; Figure 4) have considerably more fine-grained structure and higher mechanical properties of the cast material can be expected in this case. Higher material homogeneity in the total studied sample volume without conspicuous differences be-tween the superficial and internal casting part is percep-tible in this sample.Samples of castings prepared under higher casting temperature (800 °C; Figure 3) show considerably low-er homogeneity degree and considerable differences be-tween the peripheral and central part of the test sample can be found. Increased inhomogeneity of studied sam-ples can be further on augmented by the salt matrix de-composition (770 °C) accompanied with considerable generation of gaseous Cl2.Evaluation of microstructure with the aid of SEM and EDAX analysesSamples of the material that was in contact with salt cores prepared from pure salt matrix only (without ad-ditives) and squeezed with higher pressing power (200 kN), i.e. the sample 42, were chosen for this part of the experiment only.The used additives are inorganically based only with decomposition temperature considerably exceeding ex-perimental temperatures achieved during casting, so-lidification, and cooling of castings and thus it can be expected that they will have no influence on the base metal matrix. Microstructures of studied samples were evaluated from different points of measurement (Figure 5) of both the base metal matrix and other structural constituents, and the present porosity for identification of the kind of formed defects. Analyzed chemical com-position of studied samples is given in Table 2.From resulting values of EDAX analysis it is possi-ble to identify internal defects of the cast material. Gas-eous products of thermal destruction of both the salt matrix of the core itself, and the inhibitor present in the bentonite bonded moulding mixture participate in de-fects formation (Table 2). Increased concentration of chlorine and sulphur was primarily determined espe-cially in points corresponding to points of measure-ments Spectrum 4 ; 7 and 11 of the studied sample.CONCLUSIONThis contribution was aimed at checking the use of cores based on inorganic salts for casting of magnesium Table 2 Results of EDAX analysis of sample 42Name Elements/ weight %ON a M gA lS iM n Z nS C l KC aSpectrum1 1,34 42,12 0,65 55,89Spectrum2 59,27 37,49 3,24Spectrum3 94,51 5,49Spectrum4 61,77 32,24 3,68 1,06 1,25Spectrum5 54,41 43,86 0,97 0,32 0,43Spectrum6 65,12 26,19 7,20 1,00 0,33 0,16Spectrum7 22,81 0,24 3,31 2,91 0,89 2,08 0,48 1,77 0,62Spectrum8 38,81 11,25 9,05 1,69 0,36 0,13 2,38Spectrum9 56,14 41,98 0,27 0,23 0,28 1,10Spectrum10 52,79 45,75 1,03 0,11 0,31Spectrum11 62,29 31,75 4,33 1,20 0,42Figure 3 Detail of surface of sample 21Figure 4 Detail of surface of sample 41306   METALURGIJA 53 (2014) 3, 303-306P. LICHÝ et al.: INFLUENCE OF ECOLOGICALLY FRIENDLY CORES ON SURFACE QUALITY OF CASTINGS BASED...alloys. The application of salt cores for pre-casting of cavities and holes for gravity and low-pressure cast cast-ings from Mg-alloys is not known in common practice.From the point of view of chemical basis of used moulds, cores and the inhibitor, chemical processes run-ning during casting and cooling of the casting, it is nec-essary to ensure a sufficient exhausting of gases from the mould cavity for ensuring high casting quality. In case of cores used in this experiment an increased oc-currence of internal defects of cast samples has been confirmed. It was caused by interaction of generating gas with the base metal matrix. One of possibilities of achieving higher quality of cast parts is the application of spirituous preservative coatings or the use of cores with different base salt matrix.AcknowledgementThis work was elaborated within the frame of the research project TA02011333 (Technology Agency of the CR).REFERENCES[1]  K. Rusín: Slévárenství, 63 (2013) 7/8, 236-238.[2]  P. Lichý, J. Beňo, M. Cagala, J. Hampl: Metalurgija, 52 (2013) 4, 473-476.[3]  J. Przondziono, W. Walke, A. Szuła, E. Hadasik, J. Szala, J. Wieczorek: Metalurgija, 50 (2011) 4, 239-243.[4]  D. Vojtĕch: Metalurgija, 49 (2010) 3, 181-185.[5]  M. Holtzer; R. Dańko; S. Żymankowska-Kumon: Metalur-gija, 51 (2012) 3, 337-340.[6]  P. Jelínek; E. Adámková; J. Beňo; F. Mikšovský, V. Bry-ksí; M. Ficková: Technológ, 5 (2013) 2, 17-22.[7]  H. Hänsel: Giesserei, 89 (2002) 2, 74-76.[8]  M. Faller; A. Mössner: Giesserei, 96 (2009) 9, 72-74.[9]  S. Dobosz; P. Jelínek; K. Major-Gabryś: China Foundry, 8 (2011) 4, 438-446.[10]  S. Roskosz, J. Adamiec, M. Błotnicki: Archives of Foundry Engineering, 7 (2007) 1, 143-146.Note:   The responsible translator for English language is František Urbánek, Brno, Czech Republic5a Magnification 400x  5b Magnification 150x  5c Magnification 400xFigure 5 Details of microstructure of sample 42 with different extension

Influence of ecologically friendly cores on surface quality of castings based on magnesium alloys

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