Some problems pistons made from composite materials with small hysteresis to combustion engines

Novel composite ma hysteresisterials on the pistons are characterised that they occur in them multiple intermetallic phases which crystallize in the high temperature, before crystallization of the alfa+beta (Al+Si) eutectic. For forming of pre-eutectic phases, chromium and molybdenum are introduced to silumins, and for derivation of multiple increased concentration of nickel and copper and decreased concentration of magnesium are accomplished. On the basis of evaluations of mechanical and thermal loads of combustion engines pistons applying essence of composite materials of combustion engines pistons, as well requirements for combustion engines pistons, especially high loaded engines are expressed. Test results of hardness, influence of temperature of casting, test results of mechanical properties, friction coefficient and coefficient of thermal expansion are presented in the paper. The special attention devoted to so called hysteresis coefficient of thermal expansion and hysteresis of the relative elongation in function temperature and time. Courses of coefficient of thermal expansion for standard and composite material are presented. Differences of the a coefficient during heating and cooling in function temperature are relative to kind of heat treatment. Two-stage heat treatment is beneficial for the obtainment small values of the a coefficient