Optics & Laser Technology 143 (2021) 107366 Available online 2 July 2021 0030-3992/© 2021 Elsevier Ltd. All rights reserved. A state-of-the-art direct metal laser sintering of Ti6Al4V and AlSi10Mg alloys: Surface roughness, tensile strength, fatigue strength and microstructure Kashif Ishfaq a , Mirza Abdullah a , Muhammad Arif Mahmood b, c, * a Department of Industrial and Manufacturing Engineering, University of Engineering and Technology, Lahore 54890, Pakistan b Laser Department, National Institute for Laser, Plasma and Radiation Physics (INFLPR), Magurele-Ilfov 077125, Romania c Faculty of Physics, University of Bucharest, Magurele-Ilfov 077125, Romania A R T I C L E INFO Keywords: 3D printing Direct metal sintering process Aluminum alloy Titanium alloy Surface roughness Tensile strength Fatigue strength Micro-structure ABSTRACT Direct metal laser sintering (DMLS), a 3D printing technique, can produce high strength and good corrosion resistance parts. DMLS utilizes the powder particles partially melted by the laser beam. In DLMS, titanium (Ti6Al4V) and aluminum (AlSi10Mg) alloys have shown their potential in biomedical and automotive felds. This review focuses on the DMLS of Ti6Al4V and AlSi10Mg alloy powder particles. The effects of laser energy density, scanning speed, and various other parameters on the micro-hardness, fatigue strength, and microstructure of the manufactured part are presented. The review concluded that the operating process parameters and post- processing, including heat and surface treatments, performed on the printed part greatly infuence the micro- structure, hardness, and fatigue strength. Such processes increase hardness and fatigue strength. The pores and voids and satellite objects become the reason for the failure of parts. 1. Introduction According to ISO/ASTM 52900:2015, additive manufacturing (AM) is a process of joining materials to make parts from 3D model data, usually layer upon layer, as opposed to subtractive manufacturing and formative manufacturing methodologies [1-3]. The additively manu- factured components have specifc features such as extreme attention to details, resistance to creep, oxidation, corrosion, and the ability to maintain their mechanical properties even at high temperatures [4]. When AM is compared to conventional manufacturing methods, it gives positive results such as high material and resource material effciencies and excellent dimensional accuracy [5]. According to ISO/ASTM 52900:2015, Table 1 summarizes the different AM processes. Every AM process involves the following steps to achieve a 3D printed object: i. Initially, CAD software is used to build a 3D model, which is to be printed. ii. This CAD model is converted into stereolithography (STL) format (stereolithography, principally recognized AM practice, implemented as a standard in AM industry). This fle is the wedge-shaped illustration of a 3D CAD model. iii. The fle from step (ii) is sliced into several thin cross-sectional layers using a slicing software. In this step, the building orien- tation is defned. iv. The actual part is printed by a machine using CNC (Computer Numerical Control) codes based on the sliced fle. v. Post-processing steps such as surface treatments, sintering, or fnishing are usually required in the fnal step. For better understanding, the above-defned steps have been sum- marized in Fig. 1. In this review article, more emphasis has been laid on DMLS. A schematic illustration of DMLS and selective laser melting (SLM) is presented in Fig. 2. The difference between DMLS and SLM processes is in the temperature used to fuse the metal powder. SLM achieves com- plete melting of the powder through heating, while DMLS does not melt completely. Sintering provides enough heat to the powder particles that they merely weld together instead of complete melting. Another sig- nifcant difference lies in the feedstock: (a) DMLS works with metallic alloys, while SLM works best with pure metals [8]. DMLS also does not * Corresponding author at: National Institute for Laser, Plasma and Radiation Physics (INFLPR), Magurele-Ilfov 077125, Romania. E-mail address: arif.mahmood@infpr.ro (M.A. Mahmood). Contents lists available at ScienceDirect Optics and Laser Technology journal homepage: www.elsevier.com/locate/optlastec https://doi.org/10.1016/j.optlastec.2021.107366 Received 24 March 2021; Received in revised form 3 June 2021; Accepted 22 June 2021