EFFECT OF STRONTIUM AND ANTIMONY ON STRUCTURE AND MECHANICAL PROPERTIES OF HYPOEUTECTIC SILUMINS

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1 28/21 ARCHIWUM ODLEWNICTWA Rok 2006, Rocznik 6, Nr 21(1/2) ARCHIVES OF FOUNDARY Year 2006, Volume 6, Nº 21 (1/2) PAN Katowice PL ISSN EFFECT OF STRONTIUM AND ANTIMONY ON STRUCTURE AND MECHANICAL PROPERTIES OF HYPOEUTECTIC SILUMINS M. KIŠ 1, P. SKOOVSKÝ 2, Z. KUBINCOVÁ 3. University of Žilina, Faculty of Mechanical Engineering, Department of Materials Engineering, Univerzitná 1, Žilina, Slovakia SUMMARY In this contribution the effect of different modificators on microstructure (morphology of eutectic silicon) and mechanical properties (ultimate tensile strength - UTS, elongation - A) of hypoeutectic Al-Si alloy is compared. There were used two types of inoculant strontium (Sr) and antimony (Sb) and two types of hypoeutectic alloys (AlSi7Mg0.3 and AlSi10MgMn). Key words: modification, strontium, antimony, mechanical properties, silumin 1. INTRODUCTION Development of new construction materials with good strength density ratio is still actual. For this reason magnesium and aluminium alloys are nowadays used more and more in all sectors of industry. Aluminum alloys for castings are suitable for complicated and precise castings used mostly in automotive and aircraft industry. The influence from structural parameters on mechanical properties of Al-Si alloys have the morphology of the eutectic silicon, which can be positively affected by modification. The most used inoculant for hypoeutectic Al-Si alloys at present is strontium (Sr) [1, 2]. According to some authors, antimony (Sb) is thought to be the inoculant of the new generation, and its effect is in research stadium [3, 4]. 1 ing., milan.kis@fstroj.utc.sk 2 prof. ing. DrSc., petr.skocovsky@fstroj.utc.sk 3 ing., zuzana.kubincova@fstroj.utc.sk

2 This contribution is comparing the effect of different inoculants (strontium, antimony) on microstructure and chosen mechanical properties of hypoeutectic silumins AlSi7Mg0.3 and AlSi10MgMn. 2. EXPERIMENTAL METHODS Two hypoeutectic Al-Si alloys AlSi7Mg0.3 and AlSi10MgMn were used as experimental materials. Experimental materials were supplied by company SLOVALCO a.s. Žiar nad Hronom. Chemical compositions of experimental materials are shown in Tab.1. and Tab.2. Tabela 1. Skład chemiczny stopu AlSi7Mg0.3 (STN ) Table 1. Chemical composition of AlSi7Mg0.3 alloy (STN ) Element Si Mg Ti Mn Cu Sr % wt. 7,1 0,38 0,095 0,005 0,001 0,025 Element Fe Zn Ca Na P Sb % wt. 0,12 0,003 0,002 0,0008 0,0006 0,0001 Table 2. Skład chemiczny stopu AlSi10MgMn (STN ) Table 2. Chemical composition of AlSi10MgMn alloy (STN ) Element Si Mg Mn Cu Fe Zn Ti Cr Ni % wt. 9,48 0,262 0,1742 0,0011 0,309 0,006 0,017 0,0066 0,0039 Element Pb Sn Na Ca B Sr Sb P Al % wt. 0,0014 0,0011 0,0004 0,0006 0,001 0,0006 0,02 0,012 89,705 These hypoeutectic Al-Si alloys have good mechanical properties, good corrosion resistance, and are used for light highly stressed casting for automotive industry. AlSi10MgMn alloy was modified by different amount of Sr (to 0.05%) in form of AlSr5 master alloy and AlSi7Mg0.3 alloy was modified by different amount of Sb (to 0.03%) in form of AlSb10 master alloy. Experimental casts were casted in the laboratory of Department of Technological Engineering at University of Zilina from temperature 740 C into metallic form. Chosen mechanical properties were obtained by tensile test according to standard STN EN Effect of Sr and Sb addition on microstructure was evaluated on specimens etched by 0.5% HF at magnification 500x. Morphology of the eutectic silicon was evaluated by using REM after deep etching by 36% HCl. 264

3 3. RESULTS AND ANALYSIS 3.1. Structure In Fig. 1 are shown microstructures of unmodified and modified states of AlSi7Mg0.3 and AlSi10MgMn alloys with different amounts of modificators. a) AlSi10MgMn, 0 % Sr d) AlSi7Mg0.3, 0 % Sb b) AlSi10MgMn, 0,02 % Sr e) AlSi7Mg0.3, 0,005 % Sb c) AlSi10MgMn, 0,04 % Sr f) AlSi7Mg0.3, 0,01 % Sb Rys. 1. Mikrostruktura poeutektycznych stopów Al-Si, traw. 0,5%HF Fig. 1. Microstructure of hypoeutectic Al-Si alloys, etch. 0,5 % HF 265

4 Microstructure of unmodified AlSi10MgMn alloy consist of α-phase dendrites (white area) and eutectic silicon (black area) in form of small globular particles and fine rod-like particles at dendrite boundaries (Fig.1a). Addition of modificator Sr caused change in morphology of eutectic silicon particles into fine globular particles (Fig.1c). The finest microstructure is at 0,04 % of Sr, so we can consider it as optimal modified state. As we can see from Fig.1d f, addition of antimony caused no change in eutectic silicon morphology. Eutectic silicon particles in unmodified and modified states have plate-like morphology, observed as needles Mechanical properties Fig.2 shows graphic dependency of ultimate tensile strength of AlSi7Mg0.3 and AlSi10MgMn alloys on amount of modificators Sr and Sb (trend polynomial curves of third grade were approximate over measured values). Rys. 2. Zaleno granice wytrzymałoci na iloci modyfikatora Sr lub Sb Fig. 2. Graphic dependency of UTS on amount of inoculants Sr or Sb Addition of antimony up to 0,015 % Sb in AlSi7Mg0.3 alloy results in increase of ultimate tensile strength. Further increase of Sb amount results in decrease of UTS. Addition of strontium in AlSi10MgMn results in increase of ultimate tensile strength, but measured values of UTS were higher in AlSi7Mg0.3. From shapes of curves is possible to consider, that 0,015 % Sb and 0,05 % Sr are the optimal modified states. 266

5 Fig. 3 shows graphic dependency of elongation of AlSi7Mg0.3 and AlSi10MgMn alloys on amount of modificators Sr or Sb.!" Rys. 3. Zaleno wydłuenia na iloci modyfikatora Sr lub Sb Fig. 3. Graphic dependency of elongation on amount of inoculants Sr or Sb Addition of strontium results in little increase in elongation, with maximum measured value at 0,04% Sr. Increasing amount of antimony caused increase in elongation with maximum measured value at 0,005 % Sb. Higher values of elongation were measured in AlSi7Mg0.3 alloy modified with antimony. Optimal amounts of modificators from shape of curves are 0,015 % Sb and 0,04 % Sr. 4. CONCLUSIONS Results from mechanical testing and structure observation show that: addition of inoculants Sr and Sb leads to increase of ultimate tensile strength and elongation, addition of modificator Sr has more significant positive effect on change of eutectic silicon morphology compared to the effect of Sb addition. Following the effect of both modificators on structure is possible to state that in tested conditions Sr addition showed a strong modifying effect while the effect of Sb addition is possible to characterize like inoculation of α-phase (increase in number of nucleuses). This work would not have been possible without the support of the Slovak grant agency VEGA No. 1/3153/06 and No.1/2090/

6 REFERENCES [1] Tillová, E., Chalupová, M., Konená, R.: Využitie hbkového leptania pri štúdiu morfológie eutektického kremíka v zliatine AlSi10MgMn, MI 7, 2000,.1, s.61-68, EDIS ŽU Žilina, 2000, ISSN [2] Gyurgyonovicsová, O., Sládek, A., Bolibruchová, D: Ovplyvovanie mechanických vlastností a štruktúry zliatiny AlSi7Mg0.3 antimónom, MI 11, 2004,. 2, s , ISSN [3] Reif W., a kol.: Untersuchungen von Feinungswirkung und zum Feinungsmechanismus von Antimon am Beispiel der Legierung G-AlSi7Mg. Giessereiforschung 45, Nr.1, [4] Fatahalla, N. Hafiz, M. Abdulkhalek, M.: Effect of microstructure on mechanical properties and fracture of commercial hypoeutectic Al-Si alloy modified with Na, Sb and Sr, Journal of Materials Science, Nr. 34, 1999, p WPŁYW DODATKU STRONTU I ANTYMONU NA STRUKTUR I WŁACIWOCI MECHANICZNE PODEUTEKTYCZNYCH SILUMINÓW STRESZCZENIE W pracy porównano wpływ rónych modyfikatorów na mikrostruktur (morfologia krzemu eutektycznego) oraz właciwoci mechaniczne (wytrzymało na rozciganie UTS, wydłuenie A). Zastosowano dwa modyfikatory, stront (Sr) i antymon (Sb) I dwa rodzaje podeutektycznych siluminów (AlSi7Mg0.3 oraz AlSi10MgMn). Recenzował: prof. Edward Guzik. 268