## 1 Introduction  
Among different additive manufacturing (AM) techniques ranging from partial sintering to full melting, selective laser melting (SLM) process aims at the full melting of the powder material spread on the base platform by using a focused laser beam. The development side of the process can now be considered at a mature stage such that it can result in almost fully-dense components, at least for some of the materials, like steel, aluminum, titanium, as well as some of the superalloys [1; 2; 3]. Imparted energy density is the dominant factor in determining the resulting part quality in terms of relative density; however, for the components to remain functionally stable under mechanical loading, these parameters have to be investigated carefully so that their influence on the part porosity, microstructure, as well as residual stresses can be considered in designing functionally reliable components. A brief synopsis is given below about the most important aspects of the process, followed by the part properties that are specific to Al-Si alloys manufactured by the SLM process. Certain phenomena involved in the SLM process have to be understood in detail with regard to the process conditions, their behavior during the process, and their corresponding part characteristics. One of these is the balling effect, which is observed in the process due to the shrinkage of the melt pool. Uncontrolled balling is detrimental to the SLM parts in terms of its tendency to pore formation. For attenuation of this effect, factors, like oxygen content, laser power, scan speed, and hatch distance need to be controlled for obtaining the optimal feedstock wettability [4; 5]. Another important aspect of the SLM process thatcan significantly affect the resulting part is the melt pool condition affecting the local microstructural features. The role of scanning strategy in influencing a gradient microstructure using electron beam melting technology was investigated. The technology was introduced under the term \"ghost beam scan strategy\" [6]. Fine microstructures, generally obtained in the SLM process, are due to short exposure of laser energy to the feedstock powder and the consequential elevated thermal gradients giving rise to thermal stresses in the parts. A mixed microstructure, fine and coarse, depending on the local exposure, is obtained, which is generally a metastable microstructure, especially in Al-Si alloys, which can be changed by post-process exposure to temperature. Al-Si system results in dendritic microstructure in SLM--generally fine dendrites thatare coarsened at double-melt regions due to increased exposure to laser beam. For such material class, the role of temperature is important due to its effect on the solubility of Si in the matrix, as well as its rejection in the matrix. The rejected Si particles can act as a reinforcement of the matrix, but they can also be a source of crack initiation when they are large in size and inhomogeneous in morphology making the resulting material as brittle and susceptible to unpredictable failure under fatigue loading [7; 8]. Identification and controlling the thermally-induced residual stresses is a critical aspect when SLM components are to be employed in fatigue applications. Several SLM attributes drive the formation of these stresses, the time-dependent exposure being the most important one where the cooling rate in SLM creates waves of thermal expansion and contraction. Longitudinal scanning strategy results in the anisotropic development of thermal stresses, which can be controlled by following the so-called island scanning, which reduces the melt pool anisotropy [9]. Base platform can also be critical in controlling the thermal gradients where its thickness, as well as temperature, determines the resulting cooling rate. Pre-heating the platform can reduce these gradients and weaken the development of thermal stresses [10; 11], since current research proved that a gradient of microstructure and properties could be induced on a scale of 100 \(\upmu\)m [12].