AGE HARDENING RESPONSE OF AC2B ALUMINIUM ALLOY MODIFIED WITH 0.1 wt. % Sn Bondan T. Sofyan *) and Ria Kartika Department of Metallurgy and Materials, Faculty of Engineering, University of Indonesia, Kampus UI Depok 16424, Indonesia. *) Corresponding author: bondan@metal.ui.ac.id ABSTRACT The use of aluminium alloys for automotive purpose is increasing in the last two decades, due to their light weight and corrosion resistance. One type of aluminium alloys widely used in automotive is AC2B (Al-7Si-2.8Cu) as casting products. Enhancement of mechanical properties of this alloy may be achieved through addition of alloying elements and heat treatment processes. This paper discusses the age hardening response of AC2B alloy minoralloyed with 0.1 wt. % of Sn. Tensile and hardness tests were conducted to investigate the mechanical properties of the as-cast alloys, while observation on the microstructure of the materials was carried out by using light microscopy and SEM (scanning electron microscope) equipped with EDS (energy dispersive spectroscopy). Research results show that the addition of Sn for 0.1 wt. % is effective in increasing the age hardening response of AC2B alloy. A considerable amount of Sn was detected in association of Al 2 Cu particles, which indicates facilitation of this phase by Sn, which is responsible to the increased age hardening response. Modified alloys which were cast in metal mould possess higher mechanical properties than that cast in sand mould, and this was preserved during ageing. Keywords: AC2B, Al-Si-Cu, minoralloying, ageing, Al 2 Cu INTRODUCTION One foundry alloy that is popular for use in automotive application is AC2B aluminium alloy, due to its excellent castability and mechanical properties. Its excellent corrosion resistance and low costs of recycling are also important considerations from an environmental point of view [1]. Aluminium alloy AC2B is essentially a hypoeutectic Al-Si alloy with two main solidification stages, formation of aluminium rich (Al) dendrites followed by development of two-phase (Al-Si) eutectic. However, the presence of additional alloying elements such as Mg and Cu, as well as of impurities such as Fe and Mn, leads to a more complex solidification sequence. Accordingly, the as-cast microstructure of AC2B alloy presents many intermetallic phases in addition to the eutectic structure. Therefore, alloying elements possess profound impact on the properties of AC2B alloy [2]. Addition of Cu to eutectic Al-Si alloys leads to a slight increase in the alloy fluidity, and a depression in the Si eutectic temperature of ~1.8 o C for every 1 wt. % Cu added. Also, some of the mechanical properties obviously benefit from the addition of Cu as an alloying element (such as yield dan tensile strength) [2]. Copper forms an