Effect of Alloying Elements on High Temperature Mechanical Properties for Piston Alloy

Abstract

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.

High Temperature Mechanical Properties of Al–Si–Mg–(Cu) Alloys for Automotive Cylinder Heads

“…If the fatigue life only is evaluated as the plastic strain range, the fatigue life might be distorted as a result of considering the increase in elongation due to an increase in temperature neglecting the strength of the material. 13) Therefore, when the fatigue life was evaluated as the hysteresis loop energy, which considers the strength and plastic strain of the materials under the given conditions, a similar low cycle fatigue life was observed without an increase in fatigue life due to the increase in temperature, as shown in Fig. 9(b).…”

“…This can be explained by softening of the solid with increasing temperature > 0.7 T m (melting temperature), in which the general properties of the solid cannot be maintained. 13) Therefore, the reliability of the thermal expansion coefficient over 350°C is limited due to collapse of the solid. The thermal expansion coefficient decreased with increasing proportion of Si, Mn and Cu.…”

“…AlSiMg(Cu) casting alloys, as important light metals, are used widely in automotive components owing to their excellent mechanical properties and castability. 13) In recent years, diesel engines have become prevalent because of their low total emissions, and the combustion pressures of diesel engines have increased up to 20 MPa. Because many components used in automotive engines are subjected to complex loading cycles at high temperatures, 47) it is important to understand the loading mechanisms and damage accumulation, as well as increase the fatigue lives under given conditions.…”

Revealing the Effect of Local Connectivity of Rigid Phases during Deformation at High Temperature of Cast AlSi12Cu4Ni(2,3)Mg Alloys

“…The alloying elements Cu and Mg play a decisive role on precipitation strengthening of the matrix, while, together with Ni, they define the interconnectivity of the 3D networks [6,7,8,9]. These rigid networks exhibit high thermal stability and provide strength retention up to about 300 °C even after overaging of the matrix [10,11].…”

Effect of Microstructure on High Temperature Mechanical Properties of A319 Casting Alloy for Automotive Cylinder Heads

“…The thermal expansion coef cient increased with increasing temperature to 250 C, became saturated up to 350 C, and then decreased with further increases in temperature. This can be explained by the softening of the solid with increasing temperature, at which the general properties of the solid cannot be maintained 16,17) . Therefore, the reliability of the thermal expansion coef cient over 350 C is limited due to the collapse of the solid.…”