2.1 Chemical compositions
For the Additive manufacturing using LPBF, AlSi10Mg alloy was chosen. The chemical compositions were shown in the Table.1. For the stir casting process, aluminum alloy (Al8011) was chosen as matrix and Silicon Carbide (SiC) was chosen as the reinforcement particles for this conventional manufacturing process [21]. Aluminum 8011 alloy primarily consist of 98% of aluminum with significant amount of bismuth, silicon, tin, ferrous, lead, copper, zinc, few traces of magnesium and titanium. Silicon carbide is a hard covalently reinforced material dominatingly created by the carbo thermal extracted from silica normally utilizing the Acheson process. So, SiC particles with 325 mesh was used as the reinforcement particles. Table.2. shows the chemical composition of aluminum / aluminum 8011 alloy.
2.2 Stir casting process
Al-SiC 10% samples were manufactured by stir casting process. The stir casting process parameters were shown in the Table.3. At first, the furnace was heated up to 800oC and then Al-8011 aluminum alloy billets were placed inside the crucible. The working temperature of 750oC was made constant. Then the SiC reinforcement particles were introduced inside the molten aluminum melt. Stirring was carried out with 45o blade angle for a holding time of 10mins which was kept 40% from the base. Finally, the molten aluminum was poured into the mold to get the casted samples [22].
Table.1 Chemical composition of AlSi10Mg Alloy (Weight %)
Elements
|
Minimum
|
Maximum
|
S1
|
S2
|
S3
|
Manganese-Mn
|
-
|
0.45
|
0.040
|
0.040
|
0.040
|
Silicon-Si
|
9.0
|
11.0
|
10.62
|
10.57
|
10.52
|
Nickel-Ni
|
-
|
0.05
|
0.015
|
0.015
|
0.015
|
Copper-Cu
|
-
|
0.05
|
0.019
|
0.021
|
0.021
|
Titanium-Ti
|
-
|
0.15
|
0.012
|
0.012
|
0.012
|
Tin-Sn
|
-
|
0.05
|
<0.01
|
<0.01
|
<0.01
|
Zinc-Zn
|
-
|
0.10
|
<0.01
|
<0.01
|
<0.01
|
Lead-Pb
|
-
|
0.15
|
0.011
|
0.011
|
0.011
|
Iron-Fe
|
-
|
0.55
|
0.13
|
0.13
|
0.13
|
Magnesium-Mg
|
0.20
|
0.45
|
0.32
|
0.33
|
0.32
|
Others-Each
|
-
|
0.05
|
<0.05
|
<0.05
|
<0.05
|
Others-Each
|
-
|
0.05
|
0.046
|
0.033
|
0.023
|
Aluminium-Al
|
-
|
Balance
|
Balance
|
Balance
|
Balance
|
Table.2 Chemical Composition of Aluminum 8011
Elements
|
Composition (%)
|
Silicon
|
0.213
|
Iron
|
0.40
|
Copper
|
0.10
|
Manganese
|
0.018
|
Magnesium
|
0.10
|
Titanium
|
0.009
|
Zinc
|
0.210
|
Lead
|
0.009
|
Tin
|
0.030
|
Bismuth
|
0.002
|
Zirconium
|
0.002
|
Chromium
|
0.002
|
Aluminum
|
98.905
|
Table.3 Stir Casting Process Parameters.
Working temperature
|
750 0C
|
Capacity of the melting pot
|
1kg of Aluminum (max)
|
Stirring speed
|
250rpm
|
Maximum operating temperature
|
900 0C
|
Operating Voltage
|
440 V, AC three Phase 50 c/s
|
Holding time
|
10mins
|
App. Power consumption
|
4 KW
|
Impeller position
|
40% from the base
|
Preheating furnace Temperature
|
800 0C
|
Stirrer blade angle
|
450
|
Control
|
Automatic by microcontroller
|
2.3 AM based Laser Powder Bed Fusion process
AM specimens were manufactured by LPBF, with an EOS M280 system with the compressed air supply of 7,000 hPa; 20 m³/h, Yb (Ytterbium) fibre laser with nominal power of 400W, diameter of laser beam at building area 100 - 500 μm. Fig.1 shows Metal Additive manufacturing EOS M280 system. As mentioned by the manufacturer, laser power of 370 W, layer thickness of 30 μmscanning speed of 1300 mm/s and hatching distance of 190 μm were used as the processing parameters for LPBF [22]. It was make sure that all the AM samples were manufactured based on the same process parameters to analyze the micro structural and mechanical properties.
The LPBF method will provide a way to fabricate the specimens for investigations. The system involving dispenser unit caring aluminium alloy powder (AlSi10mg) with 15micron which continuously supply the metal powder during the entire printing processes. The dispenser duct was specially designed to carry the aluminium alloy powder which has high material stability [23]. The dispenser unit was connected with strong build platforms which will helps to provide a space for the development of specimens for evaluation. The high sensitive re-coater will provide a way to material frameworks. The excess amount of powder material was collected in the collector unit called as Interpretable Properties Chain Module (IPCM).The process initiates with removing oxygen content presents in the printing chamber and maintain as 0.1% level. The inert gas preferably Argon is chosen to reduce the oxidization of sintering processes to create a stable printing condition by maintaining constant pressure, keeping out the impurities, reducing the powder climbing and control the thermal stresses [24].
The Electro optical system triggers the high intensity laser beam with the range of 600-700 nm wave length by providing 1mw laser radiation which will solidify the powder particles as per the geometrical dimensions fed in to the system already [25].The laser calibration will be done for every continuous cycles. The angular rotation of the laser dispensing system will have 45˚ to 67˚ fusion. The special filter H13 and F9 comes in to function for collecting the unused and climbing powdered molecules [26]. Before initialing the process, the necessary primary verification was done with the simulation. The specimens were primarily designed using the Solidworks modelling software and it was imported to Material Magic Data Preparation Software (MMDPS) for simulation and validating the entire process Design for Additive Manufacturing (DAM) [27]. Once the simulation process was successfully validated the same parameters as fed into the Electro Optical System Builder (EOS builder) [28]. Through the EOS builder the LPBF process method will be initiated.
2.4 Micro structural analysis
Fabricated samples were cut into specimen size of 10 mm x10 mm x10 mm using the Wire cut Electric Discharge Machining process (WEDM). The specimens were analyzed for their morphology using OM and SEM analysis. The specimens were etched and polished before the analysis of the OM and SEM
2.5 Porosity measurements
The porosity percentage can be estimated by measuring the relative density of the specimen (P% + RD = 100). Relative density can be calculated by measuring the bulk density and dividing it by the theoretical density of the specimen. Bulk density can be measured using the Archimedes method. The theoretical density can be calculated employing the rule of mixtures. Part density of as built AlSi10Mg test samples tested as per ASTM B311 using the WEDM. The porosity in the specimens was determined using Eq. (1).
P = 1 - (ρ experimental/ ρ theoretical) x100
2.6 Mechanical characterizations
Tensile test performed for XY and Z direction test samples as per ASTM E8/E8M specification. The same ASTM standards were specified on both AM and SC samples. Universal Testing Machine (H50KL, Tinios Olsen Computerized model) was used for finding tensile properties (UTS, YS and % El) for the cast specimens and AM build parts. Hardness of as build AlSi10Mg test samples tested as per ASTM E10. Brinell macro- hardness tester (HR-320, Mitu Toyo South Asia Pvt Ltd), was used for finding the hardness values for both AM and SC samples. Fracture toughness for XY and Z directions as built test samples tested as per ASTM E399 (Fig 2(b)). Materials Testing System (MTS 810) with 250KN load was used to the find the fracture toughness of the samples. Shear strength for XY and Z directions as built test samples were fabricated as per ASTM E769 (Fig 2(a)). Double shear stress in Universal Testing Machine (H50KL, Tinios Olsen Computerized model) was used to find the shear strength of the AM and SC samples.