IJE TRANSACTIONS B: Applications Vol. 34, No. 08, (August 2021) 2021-2027 Please cite this article as: N. F. Soliman, D. O. Ramadan, J. A. Yagoob, Influence of Mould Thickness on Microstructure, Hardness and Wear of Al- Cu Cast Alloys, International Journal of Engineering, Transactions B: Applications, Vol. 34, No. 08, (2021) 2021-2027 International Journal of Engineering Journal Homepage: www.ije.ir Influence of Mould Thickness on Microstructure, Hardness and Wear of Al-Cu Cast Alloys N. F. Soliman a , D. O. Ramadan *b , J. A. Yagoob c a Mechanical Technical Department, Technical Institute of Kirkuk, Northern Technical University, Iraq b Mechanical and Energy Engineering Techniques Department, Erbil Technical Engineering College, Erbil Polytechnic University, Erbil, Kurdistan Region, Iraq c Technical College of Kirkuk, Northern Technical University, Iraq PAPER INFO Paper history: Received 19 April 2021 Received in revised form 09 July 2021 Accepted 13 July 2021 Keywords: Aluminium-Copper Alloys Cooling Rate Grain Size Tribology ABSTRACT Aluminium-copper alloys have a wide range of industrial applications especially in military vehicles, rocket fins and aerospace. Solidification plays a vital role in controlling the mechanical and tribological properties, and influencing the microstructure of metallic alloys in general and aluminium alloys in particular. Therefore, the researchers have made many efforts to figure out the solidification behaviour of Al-Cu alloys. Despite all these endeavors, however, the behavior is not yet fully understood. This research aims to investigate the effect of cooling rate on the microstructure, mechanical and tribological properties of aluminium-copper cast alloys (Al-Cu alloys) under dry sliding conditions. Four cooling rates were achieved by using four various steel moulds made of different thicknesses and one of them was surrounded with green sand, to get a lower cooling rate, with the same respective mould hole geometries. The microstructure results showed that the grain size increases with decreasing the cooling rate. While the hardness increased largely due to the refinement of the microstructure. Finally, it was concluded that the wear rate increases with decreasing the cooling rate, and that is due to the reduction in hardness. doi: 10.5829/ije.2021.34.08b.23 NOMENCLATURE  Linear sliding speed (m/min)  Running time (min)  Distance between the center of sample to the centre of the disc (m)   Wear rate  Disc rotational speed (RPM) Greek Symbols  Total Sliding distance (cm)  Density (g/cm 3 ) 1. INTRODUCTION 1 Aluminium and copper alloys are characterized by high strength, lightweight, resistance to high temperature, and high ductility which made them very important alloys in many industries such as military and aircraft industries as well as in transport applications and lightweight construction. Where high strength and ductility are highly needed in such kinds of applications [1]. Therefore, the mechanism of precipitation hardening in wrought and cast binary Al-Cu alloys is well understood and extensively recorded in the literature. Copper * Corresponding Author Institutional Email: dlair.o.ramadan@epu.edu.iq (D. O. Ramadan) element is considered as a great deposition-strengthening in aluminium. Adding copper improves machinability, toughness, tensile strength, and creep [2, 3]. Where, additions of about 0.05 wt.%. of copper to aluminium results in good toughness and high strength alloys after subjected to different aging including at elevated temperature (artificial aging) or at room temperature (natural aging) [4, 5]. Aryshenskii et al. [6] studied the recrystallisation process in aluminium alloys. It is well known that the microstructure of the material has a significant effect on the mechanical properties, where decreasing the grain size leads to