OBRABOTKAMETALLOV TECHNOLOGY Vol. 26 No. 1 2024 Introduction Aluminum-based alloys, due to its light weight, high strength, ductility and good corrosion resistance, are widely used in many branches of mechanical engineering [1, 2]. Aluminum is almost three times lighter than steel and is the third most abundant element on Earth. Traditional methods for producing parts from aluminum alloys are: pressure casting, gravity die casting, green sand casting [2]. In recent years, additive manufacturing (AM) has revolutionized the manufacturing industry as it has made possible to manufacture parts of complex geometric shapes directly from a 3-dimensional drawings [3, 4]. The software slices the 3D object into layers, which thickness ranges from 20 to 100 μm, while the laser moves along the predetermined trajectory and fuses layer by layer. The most common technology for layer-by-layer parts production from metal powders is selective laser melting (SLM) technology. An analysis of the literature shows that alloys based on iron, titanium, cobalt and nickel produced by this method have much better mechanical properties than the alloys produced by traditional methods [5, 6]. In aluminum-based alloys obtained by SLM, structural defects are easily formed, which lead to intense cracking. Scientists off er various ways to eliminate these defects. In the study [7], cracking was prevented by reducing the cooling rate during the SLM process and reducing heat transfer from the parts to the platform. Koutny et al. [8] investigated the infl uence of SLM process parameters (laser power, scanning speed, scanning strategy and platform heating) on the relative density and mechanical properties of specimens obtained from 2618 alloy (Al-Cu-Mn-Mg-Ag alloy) [3]. During the experiment the formation of cracks was observed in the specimens, due to the high temperature diff erence between the solid and liquid phases while solidifying. Reducing the thermal gradient due to the construction of supporting elements leads to a decrease in the number of cracks. Heating the platform to 400 °C and lower scanning speed could not improve the quality of the specimens and caused gas porosity. In a study by Reschetnik et al. it is said that the parts made of 7075 alloy (Al-Zn5.5-Mg-Cu) by the SLM method have low mechanical properties [9]. The reason for the reduced mechanical properties is cracking that occurs when hardening. The authors suggested changing the melting modes (laser power, scanning step and scanning speed) and further heat treatment to improve the mechanical properties. New aluminum-based systems are currently being developed specially for additive manufacturing. In the paper [10], the problem of cracking of specimens made of aluminum 6061 alloy (Al-Mg-Si-Fe-Cu-MnCr-Zn-Ti) was solved by adding zirconium oxide into the alloy as crystallization centers. The literature also describes that the light element magnesium signifi cantly increases the strength of the aluminum matrix through the dispersion hardening mechanism, while scandium increases the strength of the aluminum matrix through grain refi nement [11], [12]. Taking into consideration the signifi cant increase in the amount of aluminum powders used in additive manufacturing, the Aluminum Association has developed an aluminum alloy registration system known as Purple Sheets [13]. Today, the prices for commercially available aluminum alloy powders for SLM vary within the range of 40–80 US dollars per kg, those for Al-Si-Mg alloys reach up to 200 US dollars per kg. The quality and spherical shape of the powder also aff ect the price: powders produced by plasma atomization are usually more expensive than powders produced by gas atomization [14, 15]. Because of this, at present, the cost of parts produced by SLM method is much higher than those manufactured by traditional methods. To reduce the cost of products and save material, the non-fused powder can be reused [14, 15], although reused powders include soot, combustion and oxidation products, which leads to deterioration of the mechanical properties of the parts [14, 16]. The growing number of alloys currently listed in Purple Sheets [13] indicates that there is demand for a wide range of aluminum alloys for additive manufacturing. It is noted that optimal processing parameters are especially important for the wide use of SLM obtained aluminum alloys in industry [17]. This is mainly because aluminum powder has high refl ectivity and high thermal conductivity, which reduces the laser absorption of the powder [18, 19]. In addition, the oxide layers formed on the melt pool promote the porosity formation [16]. Pores and defects in SLM manufactured parts usually worsen the mechanical properties of the products.
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