Microstructural Characteristics, Mechanical Properties, Fracture Analysis and Corrosion Behavior of Hypereutectic Al–13.5Si Alloy

Abstract

Hypereutectic Al–13.5Si alloy containing 1.47% of copper and 1.30% of magnesium was designed as a potential material for internal combustion engine pistons. The optical microscopy and scanning electron microscopy (SEM) revealed the fine dendrites of α-Al phase and significantly dispersed eutectics in as-cast specimens. Several intermetallic phases were observed indicating different crystallization velocities and alloy composition nonuniformities. The tensile testing and hardness measurements performed at room temperature have shown an excellent tensile strength and hardness of as-cast specimens, but low elongation due to a complex multiphase structure. The mechanical examinations at 250 °C and 300 °C have presented a decrease in tensile strength and an increase in elongation, while hardness was slightly changed. The fractographic analysis has shown the features of the brittle as well as ductile fracture. The areas of dimples and areas containing particles with smooth surfaces were detected. Electrochemical methods, Tafel linear polarization, cyclic voltammetry, chronoamperometric measurement and impedance spectroscopy were employed to determine the corrosion behavior of as-cast specimens in 0.5 M NaCl solution. The resistant oxide layer formed on the surface was not entirely consistent due to the appearance of intermetallic phases. SEM examinations of corroded samples did not discover severe pits on their surfaces.