2. Alloys usually used for moulding the pistons No. Alloyed elements [%] Inclusions [%] Origin crt.

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1 THE INFLUENCE OF THE CHEMICAL COMPOSITION OF ALLOYS LIKE SILUMIN, OFTEN USED FOR MOULDING THE PISTONS OF THE THERMICAL ENGINES, OVER THE MECHANICAL PROPRIETIES Prof. PhD I.I. Penza ARTEMOV Russia Eng. PhD Fr. MANDEK Politehnică University, Timişoara Prof.eng. PhD I. SPOREA Eng. I. KATONA A.R. Arad Ec. Corina STOICAN Hunedoara Abstract This paper sets forth to point out the evolution of the main proprieties of the studied Siluminum alloys, which are used in order to mould the pistons for the thermical machines. In order to demonstrate the influence of the chemical composition of alloys used in order to mould the pistons of the thermical engines, the present paper analysed and made a comparison between Siluminum alloys. It also performed some tests in order to point out the evolution of the main properties of the studied alloys. 1. Introduction The use of the pistons moulded for thermical engines with aluminium, is given by the way it s exploited and we can say that: on the pistons of most thermical engines operates a high, variable level charge; they are in permanent contact with liquid and gaseous environments; the charges can reach T and the temperature of the explosive mix can reach 800 C. Because of these factors, some necessary requirements must be fulfilled/accomplished regarding the aluminium alloys intended for moulding the pistons [1] [4], aspect that was confirmed in reality trough [3], [5]. As main requirements regarding the moulded aluminium pistons we

2 can enumerate: reduce specific weight; coefficient of thermical dilatation as low as possible [6]; high thermical permeability; high hardness that maintains itself even at high temperatures (in which the piston functions) [7]; high resistance for corrosion and maintaining the structure that will avoid the growth phenomenon, and so the seizing of the piston and its growing out of use. 2. Alloys usually used for moulding the pistons Until recently the pistons for cars and tractors were moulded mainly from ATSi5Cu7MgFe (or Ni). This was very easy to process unlike other alloys, but this silumin has its problems: high coefficient of thermical dilatation, low resistance for corrosion, change (growth) of the volume that led to scratches and even to cracks/fissures. Given this situation, alloys of type started to be used worldwide for moulding the pistons LOW Ex. (table no. 1), alloys that had multiple advantages over the ATSi5Cu7FeMg. Table no. 1 Alloys of medium composition ATSi13CuMgNi(Fe) used for moulding the pistons No. crt. Origin used for Internal Combustion engines Alloyed elements [%] Inclusions [%] Si Cu Mg Ni Mn Fe Zn 1. England 12,00 0,90 2,50 0,80 0,10 2. Czech Republic 12,25 1,05 1,07 1,0 0,40 0,80 0,05 3. Germany 11,75 2,08 1,03 1,26 0,63 0,80 0,40 4. Italy 12,50 2,23 1,15 0,700 0,70 0,50 0,05 5. USA 11,20 2,00 1,00 0,70 1,03 1,00 6. Russia 12,00 1,75 1,05 1,05 0,50 0,85 0,19 7. Romania 12,00 1,15 1,25 1,05 0,35 0,80 0,20 Observations all the alloys have inclusions of Ti 0,05-0,25% and Mn 0,05-0,07%; in the German and Italian alloys Ti = 0,05-0,20% is added; the USA alloys have over 0,5% Ni inclusions. An overall look shows us that the alloys from the Table no. 1 are relatively homogenous (very close), chemically speaking, with some exceptions: the English alloy has more Mg (and Ni and Mn are only inclusions), also the Italian alloys have a high quantity of Cu and Ni. The Romanian alloy is almost a perfect copy of the Russian one. We must underline the differences between these alloys and the ATSi5Cu7FeMg alloy that these alloys:

3 higher fluidity; lower contraction; the possibility of cracks to appear is lower; higher resistance for corrosion (because they contain Si), which makes it possible for the pistons to be used for engines that work with different types of fuel. 3. The influence of the element to be alloyed over the proprieties of the alloys ATSi12+EaSi ATSi5Cu7MgNi(Fe) From Table no. 1 we conclude that the foundation of the silumin type alloys, used for moulding the pistons, could be the Romanian alloy ATSi12CuMgNi, on which tests are made (table no. 2) in order to establish the influences of Ea (without Si) over the properties (figure no. 1 figure no. 3) regarding the mechanical resistance in the case of R m traction, HB hardness and A elongation. The tests have been performed in environmental temperature (figure no. 1), also tests of long standing were made (figure no. 2). No. crt. The composition of alloys for pistons + Ea Table no. 2 Alloy Si Cu Mg Ni Mn Ti Fe Zn Sn Pb Ea (without silumin) 1 ATSi+ Ea 11,0 0,75 0,80 0, ,71 0, , ,0 0,80 0,90 0, ,71 0,15 0,20 0,06 3, ,0 1,50 0,80-0,56-0, , ,8 1,08 1,07 1,42 0,39-0, , ,4 1,30 0,97 1,48 0,28 0,15 0, , ,8 1,32 1,30 1,36 0,20-0,72 0, ,05 7 ATSi5Cu7 4,45 7,05 0,36-0,48-0, ,67 8 MgNi 4,80 6,95 0,31-0,33-0,80-0,26 0,10 8,75 Alloys

4 Fig.no. 1 The values of R m, A and HB determined at 20 C on the alloys 1 8 from Table 2 In which case tensions of δ = 5 dan/mm2 were applied, at 300 C until the samples were destroyed. Duration until fracture [h] Duration in [h]: min. max. Fig. no. 2 The influence of the tension δ = 5daN/mm 2 to the duration resistance [h] (until broken) over the heated samples at 300 C (table no. 2) for the minimal and maximal values The φ 10 mm samples were moulded in shaping mixtures and were subjected to the ageing process (heated at 200 C, for 12 h and cooled in open air). In order to point out the influence of Ea, towards the foundation of the 12% Si alloy, in figure no. 3 we can see the influence of Ea over the properties of the ATSi12+Ea alloys determined in environmental temperature. Fig. no. 3 The influence Ea over the proprieties of samples (( )10 mm) on the aluminium alloys intended for moulding ATSil2+Ea;

5 HB ; R m ; A 4. Conclusions From the tests made in order to point out the evolution of the main proprieties of the studied Siluminum alloys, which are meant for moulding the pistons for the thermical machines: alloys 1 and 3 (alloys that contain low amounts of Cu and Mg) have long technical resistance in the inferior limit; alloys that contain Cu and Mg in the inferior limit (alloy 6 and alloy 4) that contains also Mn, have long technical resistance in the superior limit; the variation of Cu between the 0,5-4,5% limits leads to the substantial growth of the long technical resistance at 300 C without having a substantial influence on the mechanical resistance at environmental temperature (the bonds of the solid solution α, alloyed with Mn and Mg and other analogue elements, grow). After the decomposition of the alloyed solid solution α, formations of the T phase appear (Al2Mn2Cu) that creates micro-heterogeneity in the interior of the grains/granules α, which leads to the unification of their deformations; the cooper in excess, takes part in forming the phase that contains Ni-T (Al6Cu3Ni) phase that crystallizes in the branched formation and its particles lay on the separation limits of the solid solution α, blocking them and trough this an essential growth of the refractivity of the Al alloy is ensured; the content of CuSe is limited to 3%, because the phase CuAl2 appears, that makes the alloy fragile, decreases the resistance for corrosion and produces the growth of the pistons; the magnesium doesn t have a big influence on the refractivity, even if it leads to the growth of the mechanical temperature; the Ni leads to a big growth of the refractivity of the Al alloy (the temperature of the grains α limits grows) so we have to have 0,8-1,3% Ni in alloys; the cumulated action of the Ea from ATSi12+Ea leads to the growth of HB, a decreased Rm, while the elongation has a insignificant variation for the mechanical tests at environmental temperature; the mechanical proprieties obtained on the ATSi12+Ea type alloy recommends, as favorable chemical composition: Si = 11-13%; Cu = 1,5-3%; Mg = 0,8-1,3%; Ni = 0,8-1,3%; Mn = 0,3-0,6%; Ti = 0,05-0,2%; no more than 0,8% Fe; 0,5% Zn; 0,02% Sn; and even 0,1 %Pb.

6 References [1] Apostolescu, N., Batoga, N., Engines with internal combustion, Didactică şi Pedagogică Publishing House, Bucharest, 1967, p. 51. [2] Banarescu, M., Engines with internal combustion, Tehnică Publishing House, Bucharest, [3] Koldnev, I.F., Jaroprocinosti liteinah aluminievah, Splavov Moskva, Metallurghia, 1973, pp [4] Mandek, Fr., s.a. The influence of the ATSi12CuMgNi alloy modification over the DACIA pistons proprieties, Anal. of the Univ. of Oradea, vol. III (XIII), 2004, Fascicle of MTE. [5] Mandek, Fr., s.a. Practical tests that use modified Al alloys, moulded as pistons, Cluj-Napoca, Tehn. Univ., T.S.M.A., [6] Sporea, I., The influence of the heating temperature and of the length of time over the values of the dilatation of the thermical coefficient, BSTB (22), 1963, Fasc. 2. [7] Sporea, O., Bagiu, L., Studies regarding the effect of the thermical treatments an the behavior of the Al alloys, moulded in pieces, in exploitation, The 16 th Communication Session SECOMAR 1999, vol. I, Constanţa.