Influence of Intermetallic Compounds on Age Hardening of Gasoline Pistons in Engine Operations

Abstract

Intermetallic precipitates hold the tensile strength of alloy at elevated temperature along with enhanced mechanical and thermal properties. In this research work, we have implemented the new material development of Al-Si alloys with Fe-rich intermetallic precipitates for piston application in order to study the influence of intermetallic compounds (IMCs) on piston performance under engine operations in such a way that pistons with three different intermetallic compositions namely type A, type B and type C were developed to investigate the influence of IMC on age hardening. Three IMC pistons were installed in the engine and allowed to run for six consequent engine operations (1-6 hrs). After the designated hours of engine operation, piston was dismantled from the engine and cut sectioned for aging characterization. Hardness, an indicator of age hardening and thermal stability of the material, was measured at various piston zones such as crown, ring land, top land, skirt and gudgeon pin boss. These hardness values reflect the tendency of age hardening of pistons. It was found that higher IMC density piston alloys (type B and type C) showed the enhancement in tensile strength and hardness about 8 and 13%, respectively. Aging behavior of type B and type C piston zones has been predicted as better due to presence of high dense intermetallic compounds in comparison with type A piston. DSC testing showed that type B and type C have longer precipitation than that of type A piston. Type B and type C alloys have exhibited 20-40% higher specific heat capacity than type A piston. It was found that the high dense star-/Chinese script-like IMC has influenced the Al-Si piston alloy to enhance its properties and piston performance as well.