To improve the fuel efficiency and reduce automobile emissions, there has been growing demand of more durable alloys for engine components with the improved thermal and fatigue resistance. This study examined the effect of alloying elements on the high mechanical behavior of AlSiMg(Cu) casting alloys for cylinder heads. Depending on the alloying elements affecting the strength of the matrix, the thermal expansion coefficient decreased with increasing Mn and Cu content at high temperatures with a concomitant increase in the elastic modulus, hardness and tensile strength. Quantatative analysis showed that the mechanical properties of the Al 2 Cu precipitate hardened alloy were maintained at temperatures over 250°C, whereas the degradation of mechanical properties of the Mg containing alloy occurred at 170°C due to coarsening of the Mg 2 Si precipitation phase. The LCF (low cycle fatigue) lives decreased with increasing alloy content according to the Coffin-Manson relation due to the smaller elongation. On the other hand, an analysis of the fatigue lives with the hysteresis loop energy, which consists of both strength and elongation, showed that the fatigue lives were normalized with an alloy of the same strengthening mechanisms regardless of the test temperature.

Recent legislative and environmental pressures on the automotive industry to produce light-weight fuel-efficient vehicles with lower emissions have led to a requirement for more efficient engines. Therefore, combustion pressures of diesel engines have increased up to 20 MPa and the more durable alloys for pistons are thus necessary to increase the thermal and fatigue resistance. The demand for more efficient engines is resulting in components operating under severe stress and temperature conditions. During start/stop of engine cycles, LCF (low cycle fatigue) phenomena is generated due to the thermal transient, also HCF (high cycle fatigue) and creep deformation occur under the steady-state engine temperature during operation of engine. A quantitative study of the effect of alloying elements on mechanical behavior of Al12 mass%Si casting alloys for piston has been conducted. In the condition of minimizing casting defects, the influence of compounds features on the high temperature mechanical performance became more pronounced. Depending on Ni and Cu content affecting the strength of the matrix, the tensile strength was increased with Ni and Cu content, whereas the elongation was increased in the reverse case. Also, creep resistance was drastically increased with Ni and Cu contents mainly due to prevention of deformation owing to the increased eutectic and precipitation particles. LCF lives were decreased with alloy contents in CoffinManson relation because of the smaller elongation, but the analysis of fatigue lives with hysteresis loop energy which consists of both strength and elongation showed that the fatigue lives were normalized regardless of chemical compositions and test temperature.

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