Vol.:(0123456789) 1 3 Metals and Materials International https://doi.org/10.1007/s12540-019-00498-7 Infuence of Heat Treatment on High‑Cycle Fatigue and Fracture Behaviors of Piston Aluminum Alloy Under Fully‑Reversed Cyclic Bending Saeid Rezanezhad 1  · Mohammad Azadi 1  · Mahboobeh Azadi 2 Received: 4 July 2019 / Accepted: 6 October 2019 © The Korean Institute of Metals and Materials 2019 Abstract In the present article, the infuence of the heat treatment on high-cycle fatigue and fracture behaviors of piston aluminum– silicon alloys was studied. For this objective, standard samples were tested under fully-reversed cyclic bending by a rotary fatigue machine and then, fracture behaviors were investigated by the feld emission scanning electron microscopy. Before experiments, two heat treatments were performed on as-cast aluminum specimens, including a cooling process on samples after casting and the T6 treatment (solutioning for 5 h at 500 °C, quenching and ageing for 9 h at 180 °C). Obtained results showed that the heat treatment changed the distribution and the size and of silicon phases in the aluminum matrix and increased the hardness, signifcantly. In addition, the high-cycle fatigue lifetime increased by the heat treatment, surprisingly as 2146% and 411%, at the highest stress level and the lowest stress level, respectively. This enhancement was more than the improvement by cooling samples after casting. Observing cleavage and quasi-cleavage marks on the specimen fracture surfaces was the reason for the brittle fracture behavior. Besides, cleavage planes were smaller in heat treated samples, with shorter micro-cracks or lower crack densities, which afected the fatigue lifetime of the material. Keywords Heat treatment efect · Aluminum–silicon alloy · Engine piston · High-cycle fatigue · Fracture behavior 1 Introduction Pistons in combustion engines are complicated compo- nents, which are exposed to thermo-mechanical loadings [1–3]. Damage mechanisms in pistons have various roots, which are mainly fatigue and wear phenomena [4]. Silva [4] concluded that the fatigue phenomenon is not related to dominant damages. However, it should be considered on the design of engine pistons by engineers, especially in diesel engines. Nowadays, another efort is to reduce the fuel consumption and to increase the power increase in automotive industries. This objective will be satisfed by the weight reduction, where higher stresses may occur. To consider all mentioned requirements, based on the fatigue phenomenon, there are several concepts available that could be utilized to improve the design of pistons [4]. There are several researches about engine pistons, for new geometries, novel materials, advanced manufacturing methods [4], and diferent strengthening processes. One method is the heat treatment process, which has been investigated in this study. Before, a literature review on fatigue properties and fracture behaviors of aluminum alloys was performed in following paragraphs. Caton et al. [5] studied the infuence of the heat treatment and the solidifcation time on fatigue properties in the alu- minum alloy, with small cracks. They considered two condi- tions, including peak-aged (T6) and over-aged (T7) treats. Their results showed a signifcant efect of the T6 condition on the strength. However, the crack growth rate was slower, comparing to that of the T7 condition. Boileau and Allison [6] found the efect of the heat treatment and the solidifca- tion time on fatigue behaviors of the 319 aluminum alloy. They implied that when the solidifcation time increased, the pore diameter enhanced and therefore, the fatigue lifetime reduced. * Mohammad Azadi m_azadi@semnan.ac.ir 1 Faculty of Mechanical Engineering, Semnan University, Semnan, Iran 2 Faculty of Material and Metallurgical Engineering, Semnan University, Semnan, Iran