Journal of Mechanical Engineering Science and Technology ISSN 2580-0817 Vol. 6, No. 1, July 2022, pp. 9-22 9 DOI: 10.17977/um016v6i12022p009 Surface Quality of Fe, Ni, and Cr added Hyper-eutectic Al-Si Automotive Alloys under Up-milling and Down-milling Operation Akib Abdullah Khan 1 , Mashiur Rahman Shoummo 1 , Mohammad Salim Kaiser 2* 1 Department of Mechanical Engineering, Bangladesh University of Engineering and Technology, Dhaka-1000, Bangladesh 2 Directorate of Advisory, Extension and Research Services, Bangladesh University of Engineering and Technology, Dhaka-1000, Bangladesh *Corresponding author: mskaiser@iat.buet.ac.bd Article history: Received: 26 March 2022 / Received in revised form: 25 April 2022 / Accepted: 25 May 2022 ABSTRACT Effect of the elements Fe, Ni, and Cr on the surface quality under machining of hyper-eutectic aluminium- based Al-Si automotive alloys has been carried out as the elements improve the properties of this alloy. Machining is done on a horizontal type milling machine using a high-speed steel slab milling cutter in dry condition. Only the cutting speed varies throughout the experiment, while the machining feed and depth of cut remain fixed. The experimental results show that the addition of these alloying elements increases the roughness and hardness specially due to formation of Fe-rich intermetallic − 5 . However, the needle-like − 5  has been refined with the addition of Cr, as seen by the microstructure. The SEM fractography shows a huge cleavage of the brittle − 5  phase, which initiates the crack propagation for Fe added alloys. The downward force causes compressive stress exerted in down-milling operation, so the results depict higher hardness and better surface finish. Besides, shorter chips are formed in down- milling than up-milling process, which rather causes the brittleness of the alloys. When the cutting speed is raised, the surface quality deteriorates due to high temperature, while the hardness improves initially due to formation of precipitates then decreases due to coarsening of precipitates. Copyright © 2022. Journal of Mechanical Engineering Science and Technology. Keywords: Chips, hardness, microstructure, roughness, surface I. Introduction Al-Si alloys are used to manufacture connecting rods, pistons, cylinder liners, engine blocks, etc., components of engine construction in automotive applications, as they are light in weight and have high strength [1]-[5]. To develop the diverse properties of this alloy, several other components are added. When minor elements Cu and Mg are alloyed, it improves the involuntary properties. Moreover, the alloy offers the quick response to heat treatment [4], [5]. Iron is found in aluminum as the most common impurity. Small amount of iron into pure alloys provides slightly higher strength [6], [7]. The addition of Ni effectively increases the properties associated with the elevated temperature of the Al-Si alloy. A number of complex thermally stable intermetallic are formed, which enhance the mechanical properties of the alloys, especially at higher temperatures ahead of 250 °C [8], [9]. The acceptance of higher amount of Fe in Al-Si alloy can be effectively enhanced by adding Ni [10]. Chromium is alloyed to aluminium alloys for controlling the grain structure, preventing the grain growth and to slow down the recrystallization during heat treatment. Chromium reduces aluminum susceptibility and stress corrosion improving the toughness