Abstract
Keywords - Combustion Engines, Engine Piston, Composite Alloys, Thermal Expansion, Emissions
An object of the paper are novel pistons from composite alloys of high mechanical and functional proprieties for future combustion engines allowing on the further decreasing of the level of exhaust gases emission, noise and weight, and - what to these it is going - durability of combustion engines. As a result additions of additives into alloys, decreasing of the coefficient of thermal expansion was obtained, besides, what is most essential, also the decreasing of the differences of values of the coefficient during heating and cooling piston were obtained. Worked out novel silumins on pistons for combustion engines, which have high mechanical properties within the range of piston higher operating temperatures, 100-300°C, are introduced in the paper. Silumins contain enlarging concentration of the nickel and copper alloy additives up to 4.0, and chrome and molybdenum alloy additives up to 1.0%. The silumins are marked as AlSi12MgCr1Mo1Ni4Cu4 or AlSi17MgCr1Mo1Ni4Cu4. For example at the 250°C temperature they have following mechanical properties: Rp0.2=120-190MPa, Rm=160-230MPa, A5=3.0-6.0% and HB=90-130.
Up to the present applied silumins on pistons in this temperature have considerably lower mechanical properties, namely: Rp0.2=90-130MPa, Rm=110-140MPa, A5=1.0-8.0% and HB=60-90. So novel materials on pistons are characterized by increased values of Rp0.2 (about 40%), Rm (about 50%), HB (about 40%) at the same level value of A5. Increasing of mechanical properties of alloys is due a creation of multiple phases of the AlSiCrMoNiFeCu type of the large dispersion, decreasing of silicon quantity in eutectic, very small silicon granulation up to of 0.3-1.0m. Occurrence of given microstructure in piston-silumins results in almost the same values of the coefficient thermal expansion during the heating up to the 300°C temperature and during the next cooling into the ambient temperature. Small values of the coefficient of expansion of thermal and small differences between values of the coefficient of thermal expansion during heating and cooling enable on application of small values of working clearances between piston and the cylinder liner. As a consequence they make possible, the low exhaust emission level, and the low noise level. Unquestionable advantage novel of silumins is also the high wear adhesion resistance, comparable with the martensite microstructure in steels. The pistons from alloys with small values of the coefficient of thermal expansion, small differences of this coefficient during heating and cooling are novel aspects presented in paper. Research results of strength and metallographic parameters, research results of the coefficient of thermal expansion, comparative engine research results are represented in the paper.
The pistons for the spark-ignition and heavy duty diesel engines can be made from the novel composite silumin alloys, AlSi12MgCr1Mo1Ni4Cu4 and AlSi17MgCr1Mo1Ni4Cu4 respectively.