Effect of Zr Addition on Selected Properties and Microstructure of Aluminum Alloy AlSi5Cu2Mg

Abstract The hypoeutectic aluminum alloy AlSi5Cu2Mg is used for the production of high-strength cylinder head castings. The alloy is unique for its specific low permitted Ti content (0.03 wt% max), which makes it impossible to refine the grain structure of this alloy using standard Al–Ti–B grain refiners. The specific chemical composition is specified by the supplier company. The aim of this paper is to find a suitable alloying element that would improve the selected properties (e.g., mechanical, and physical properties) that are crucial for cylinder head castings. The research focuses on the investigation of the effect of different Zr addition (0.05; 0.10; 0.15 and 0.20 wt% Zr in the form of AlZr20 master alloy) on the properties of AlSi5Cu2Mg in the as-cast state and after heat treatment T7. The obtained results showed that ultimate tensile strength, yield strength, hardness, and physical properties of as-cast samples do not change significantly with increasing Zr content. The experimental alloys showed a more significant increase in ultimate tensile strength, yield strength, hardness, and thermal conductivity after heat treatment T7. Zirconium-rich intermetallic phases were observed in the shape of separate thick needles or as a cluster of two crossed thinner needles.