# Experimental Investigation on the Average Surface Roughness (Ra) of AlSi10Mg Alloy Manufactured by Laser Powder Bed Fusion Method

Authors: Mohamad Reda A. Refaai; D. Prakash; Jaya Christiyan K G; DVSSSV Prasad; E. Archana; Agegnehu Shara Shata
Journal: Advances in Materials Science and Engineering
 (2022)

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## Abstract

AlSi10Mg alloy is an extensively utilised material having good mechanical qualities. The laser powder bed fusion procedure has been applied for fabricating the aluminium alloy (AlSi10Mg) plates in this research. Different exposure periods and scan techniques were applied in this work to measure the average roughness. Results demonstrate that the energy density grew and roughness reduced at first and then improved. Furthermore, there were considerable differences in roughness throughout the created faces. At 125 J/mm3 and 180 J/mm3, excellent surface quality was attained. By this experiment, it was noticed that the direction of scan, wiper movement, and gas flow are the key parameters.


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## Body

## 1. Introduction

Since 1985, additive manufacturing of metals and alloys has attracted researchers and industrial experts. Huge efforts have been made to prove several aspects of this metal production procedure, including the technological aspect [1], the metallurgical aspect [2], and the design aspect [3]. Laser powder bed fusion, sometimes known as laser fusion, is a technique that uses lasers to fuse powders in a bed. SLM has become one of the most used methods of laser melting [4]. In real-time practice, the laser bed fusion method has been used in the production of a number of products such as steel [5], titanium [6], nickel [7], and aluminium alloys which are some of the real-time examples. The capacity to manufacture unique components without the use of part-specific equipment is one of the advantages of LPBF technology. Laser powder bed fusion is a well-known innovative technology for developing and manufacturing high-performance components for aerospace and automotive applications [8]. Aluminium alloys are attracting attention as construction material for parts with a high strength-to-weight ratio, low cost, and damage tolerance [9]. In comparison to alloys such as stainless steel SS 316L, Inconel 718, and titanium alloy (Ti6Al4V) [5], the printability of aluminium alloy is inferior [10]. Due to a slight change in phase 2 and solidus temperature near the two series, six series, and seven series of superalloys, only near-eutectic casting alloys like AlSi12 and AlSi10Mg are relatively simple to produce. As a result, one of the solutions to this issue is the introduction of different Al alloys which are specifically developed for the laser powder bed fusion process, primarily through silicon addition [11].This study examined the properties of laser power (P), scan speed (S), and hatch on the mechanical properties and microstructure of a high thermal conductivity aluminium matrix 6063 produced by laser powder bed fusion. Around crack, the element dispersion and grain misorientation were examined. The bulk of cracks were found to just be parallel to the property’s direction. By raising the scanning speed, the crack density was reduced. The directed fracture causes anisotropy in mechanical characteristics [12]. Several materials appropriate for this process, notably aluminium alloys, appear to be in demand in the industry. This study used laser powder bed fusion to perform a thorough examination of the machinability of aluminium six series alloys. The influence of process parameters on the microstructure A9618 specimens, particularly improved preheating process [13], was investigated.Additive manufacturing is the technical term for printing technology, a computer-controlled technique that produces three-dimensional things by layering materials in levels. Additive manufacturing such as 3D printing enables the creation of novel parts with complicated structures and also latest design alternatives for difficult components. On the other hand, high surface roughness is a significant constraint [14]. Surface roughness is an important parameter in the manufacturing of any metallic components. Aluminium magnesium metal matrix composites were fabricated by using the laser powder bed fusion. The conversion from a computer-aided design model to stereolithography and the choice of process parameters significantly affected roughness in this study [15]. From the previous works, it was observed that additive manufacturing is one of the new technologies that allows to manufacture complex-shaped metallic parts. This study looks into the effect of laser powder bed fusion process parameters on surface roughness during manufacturing an aluminum alloy (AlSiMg10 alloy).


## 2. Materials and Methods

The equipment used for this research is EOSINT M290 three-dimensional printing machine. The machine is controlled by a ytterbium laser (wavelength 1080 nm) and a laser power (450 W). This laser method is better than micromachining because it burns material away instead of moving it to other parts of the object. The schematic of the laser powder bed fusion process is depicted in Figure1 [16].Figure 1
Schematic involved in laser powder bed fusion process.For laser focusing, a concentrated spot size of 90µm can be employed. Here deflection of laser is provided by two galvanometric scanning mirrors. The procedure can be carried out in an argon environment with a low oxygen level of less than 0.13%. In order to remove the byproducts, this environment within the chamber is cycled and filtered through filter. Figure 2 depicts an aluminium alloy that was created utilising the additive manufacturing process. Table 1 shows the STL setting values used for the experiment [17].Figure 2
Fabricated aluminium alloy samples.Table 1
STL setting values.
SamplesNumber of trianglesDimension file (MB)Angle (degrees)Deviation control (mm)12078102300.06132453431100.02543790031.600.50.0024The AlSi10Mg alloy is made up of aluminium alloyed with silicon with a mass fraction of up to 10%, limited quantities of magnesium, and other negligible components. The addition of silicon makes the alloy tougher and harder than pure aluminium due to the development of Mg2Si precipitate. Due to the spontaneous production of an oxide layer on the surface of the aluminium alloy, the material has a good corrosion resistance, which can be further increased by chemical oxidation treatment [18]. The process parameters for aluminium alloy samples are shown in Table 2.Table 2
Process parameters used for aluminium samples.
ParameterConditionPower (P) (W)175–375Scan speed (mm/sec)400–1000Hatch distance (mm)0.10–0.14Energy density (J/mm3)54.2–114.6


## 3. Result and Discussion

### 3.1. Deviation between STL Model and AlSi10Mg Alloy

The STL files were matched to the samples produced. The results of the variance between the STL model and the actual result are listed in Table3.Table 3
The deviation between STL model and AlSi10Mg alloy.
TrialsDeviation (mm)Sample 10.1267Sample 20.0768Sample 30.0497Sample 40.0921Sample 1 and sample 4 have the greatest variances. In general, there is a bigger variation at the lower level near the edges in all samples. Thermal stress or a parameter setup error can both cause this discrepancy. The edge operation is linked to the contour operation in some LPBF software, and some of the parameters that control the contour operations also influence the edge procedure [19]. The maximum allowed distance from the edge scanning path to a prototype is represented by a function of the offset values.


### 3.2. Surface Roughness (Ra) at Different Zones

From Table4, it was noted that minimum surface roughness was obtained in zone 3. The previous layer’s surface roughness, which is comparable to the layer thickness, on the other hand, can cause interference also with blade. Figure 3 depicts the surface roughness of the manufactured metal sheet measured in different zones [20, 21].Table 4
The result of surface roughness (Ra) in different zones.
Sample no.Roughness zones1234112.4310.434.6514.54211.8911.653.9115.56410.7812.092.8716.87Figure 3
Surface roughness obtained in different zones for the fabricated aluminium alloy (AlSi10Mg alloy).Furthermore, the recoating blade pushes a lot of powders against the sharp end of the part being produced, causing dynamic pressure. It is possible that the difference between samples 2 and 4 is related to their differing orientations [22]. Walls made along the Y-axis, or parallel to the blade, are more sensitive to force produced by interaction between the part and the blade than walls formed along the X-axis. As a result, to shorten the contact length, the part must be rotated at a moderate angle.


## 3.1. Deviation between STL Model and AlSi10Mg Alloy

The STL files were matched to the samples produced. The results of the variance between the STL model and the actual result are listed in Table3.Table 3
The deviation between STL model and AlSi10Mg alloy.
TrialsDeviation (mm)Sample 10.1267Sample 20.0768Sample 30.0497Sample 40.0921Sample 1 and sample 4 have the greatest variances. In general, there is a bigger variation at the lower level near the edges in all samples. Thermal stress or a parameter setup error can both cause this discrepancy. The edge operation is linked to the contour operation in some LPBF software, and some of the parameters that control the contour operations also influence the edge procedure [19]. The maximum allowed distance from the edge scanning path to a prototype is represented by a function of the offset values.


## 3.2. Surface Roughness (Ra) at Different Zones

From Table4, it was noted that minimum surface roughness was obtained in zone 3. The previous layer’s surface roughness, which is comparable to the layer thickness, on the other hand, can cause interference also with blade. Figure 3 depicts the surface roughness of the manufactured metal sheet measured in different zones [20, 21].Table 4
The result of surface roughness (Ra) in different zones.
Sample no.Roughness zones1234112.4310.434.6514.54211.8911.653.9115.56410.7812.092.8716.87Figure 3
Surface roughness obtained in different zones for the fabricated aluminium alloy (AlSi10Mg alloy).Furthermore, the recoating blade pushes a lot of powders against the sharp end of the part being produced, causing dynamic pressure. It is possible that the difference between samples 2 and 4 is related to their differing orientations [22]. Walls made along the Y-axis, or parallel to the blade, are more sensitive to force produced by interaction between the part and the blade than walls formed along the X-axis. As a result, to shorten the contact length, the part must be rotated at a moderate angle.


## 4. Effect of Process Parameters on Surface Roughness

In this investigation, laser power, scan speed, hatching distance, and energy density were selected as process parameters. Surface roughness was measured at various zones on the fabricated AlSi10Mg alloy surfaces. Mitutoyo surface roughness testing equipment was used to evaluate the surface roughness at various zones [13, 23]. Table 5 shows the average surface roughness obtained during the fabrication of AlSiMg10 alloy using the laser powder bed fusion process.Table 5
Average surface roughness (Ra) obtained during the laser powder bed fusion process.
Experimental trialPower (W)Scan speed (mm/sec)Hatching distance (mm)Energy density (J/mm3)Surface roughness (Ra)11004000.107516.4521006000.125015.6731008000.1410014.6741804000.1010015.6751806000.127515.8961808000.145016.0673604000.105015.9383606000.1210016.1293608000.145015.95Even though the optimised process effectively reduced the roughness of the LPBF-produced part, variations in other surfaces were not eliminated. The “filleting effect” and “stair stepping impact” have been attributed to the phenomena of the Ra on the top face being considerably smaller than the Ra on the side in laser powder bed fusion-produced components with an angle of inclination. From Table5, it was observed that the surface roughness obtained was 15.82 µm. In this current work, scan speed is the significant parameter which reduces the surface roughness. The hatch offset is frequently chosen to decrease porosity in the LPBF process, although this results in steps on the sides between interlayers. As shown in Figure 4, When components are created horizontally, enough powder is obtained and adheres to the bottom surface melt pool, resulting in a rough side inside the part [24].Figure 4
Surface roughness measurement in different zones.


## 5. Conclusion

In this work, AlSiMg10 workpiece was fabricated using the laser powder bed fusion process. Surface roughness at different zones (zones 1, 2, 3, and 4) of the fabricated samples was evaluated. From this work, it was observed that the average surface roughness obtained was 15.92µm. It was concluded that the scanning speed is the significant process parameter which affects the surface roughness.



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