The morphological investigation of fabricated AMF (for sample 9 reported in Table 3) was performed using SEM and depicted as shown in Fig. 7 (a-b). It shows that the homogeneous porous nature resulted from the dissolution of wax powder during the sintering process in the powder metallurgy technique.
The EDS analysis for the above reported AMF sample is depicted in figure 8. The dark gray matrix phase is composed of (Al-Fe-Si). The other elemental compounds observed through EDS spectra are C, O, Mg, Ca, and Ti. The details of the EDS spectra value considered in weight and the atomic percentage are shown in table 4.
Table 4. The elemental composition present in AMF specimen
Element
|
Weight %
|
Atomic %
|
C
|
24.76
|
40.89
|
O
|
9.83
|
12.18
|
Mg
|
0.66
|
0.53
|
Al
|
60.04
|
44.13
|
Si
|
0.47
|
0.33
|
Ca
|
3.01
|
1.49
|
Ti
|
0.13
|
0.05
|
Fe
|
1.09
|
0.39
|
An X-ray Diffraction (XRD) study shows the crystallographic phases within the prepared specimen (for sample 9 reported in Table 3). This XRD technique is carried out at room temperature, and it gives evidence that the prepared specimen with a foaming agent as a wax powder (C3H6O3) shows the highest peak at 38 degrees, as shown in figure 9.
The effect of various input process parameters like powder size, sintering speed, sintering temperature, and foaming agent content on the mechanical properties of the developed AMF like porosity (%), compressive, tensile, and flexural strengths using the Taguchi DOE approach is discussed in below section.
3.1 Effects of factors and ANOVA
3.1.1 Effects of process factors on Porosity %
The data acquired using DOE L9 orthogonal array for output parameters, i.e., porosity (%), compressive, tensile, and flexural strengths, are transformed into S/N ratios listed in Table 5, 6, 7 8, respectively. The significant factor's percentage (%) contribution is reported by ANOVA analysis for the respective output properties. The percentage contribution of significant factors on the % porosity is reported in ANOVA table 5.
Table 5. ANOVA results for Porosity (%)
Source
|
DOF
|
Adj. SS
|
Adj. MS
|
F-Value
|
P-Value
|
Percentage of contribution
|
A
|
1
|
18.3568
|
18.3568
|
13.06
|
0.022
|
74.14
|
B
|
1
|
0.3427
|
0.3427
|
0.24
|
0.647
|
1.38
|
C
|
1
|
0.1014
|
0.1014
|
0.07
|
0.801
|
0.41
|
D
|
1
|
0.3377
|
0.3377
|
0.24
|
0.650
|
1.36
|
Error
|
4
|
5.6208
|
1.4052
|
|
|
22.70
|
Total
|
8
|
24.7594
|
|
|
|
|
The ANOVA results showed that powder size significantly affects % porosity (p = 74.14%), followed by sintering speed (p = 1.38%), wt. % of foaming agent (p = 1.36%), and sintering temperature (p = 0.41%) depicted minimum important and significant contributions to % porosity. The main and interaction plots depict individuals and affect their interaction on % porosity, as shown in figure 10.
3.1.2 Effects of process factors on compressive strength
The percentage contribution of significant factors to the compressive strength is reported in ANOVA table 5. For compressive strength, it was observed that powder size has a significant influence (p = 85.02%), followed by wt. % of foaming agent (p = 81.20%), sintering speed (p = 8.58%) and sintering temperature (p= 0.96%) depicted least significant contributions to compressive strength. The main plot and interaction plot depicts individuals and their interaction effects on compressive behavior, as shown in figure 11.
Table 6. ANOVA results for Compressive Strength (MPa)
Source
|
DOF
|
Adj. SS
|
Adj. MS
|
F-Value
|
P-Value
|
Percentage of contribution
|
A
|
1
|
16.6001
|
16.6001
|
113.27
|
0.000
|
85.02
|
B
|
1
|
1.6748
|
1.6748
|
11.43
|
0.028
|
8.58
|
C
|
1
|
0.1873
|
0.1873
|
1.28
|
0.321
|
0.96
|
D
|
1
|
0.4760
|
0.4760
|
3.25
|
0.146
|
81.20
|
Error
|
4
|
0.5862
|
0.1465
|
|
|
3.00
|
Total
|
8
|
19.5244
|
|
|
|
|
3.1.3 Effects of process factors on tensile strength
The % contribution of significant factors to the tensile strength is reported in ANOVA table 6. For tensile strength, it was observed that powder size has the greatest influence (p = 70.69%), afterwords by sintering speed (p = 13.38%), sintering temperature (p = 4.69%), and wt. % of foaming agent (p = 2.70%) depicted least significant contributions to tensile strength. The main and interaction plots depict individuals and their effects on tensile strength, as shown in figure 12.
Table 7. ANOVA results for Tensile Strength (MPa)
Source
|
DOF
|
Adj. SS
|
Adj. MS
|
F-Value
|
P-Value
|
Percentage of contribution
|
A
|
1
|
3.6452
|
3.6452
|
33.16
|
0.005
|
70.69
|
B
|
1
|
0.6902
|
0.6902
|
6.28
|
0.066
|
13.38
|
C
|
1
|
0.2420
|
0.2420
|
2.20
|
0.212
|
4.69
|
D
|
1
|
0.1395
|
0.1395
|
1.27
|
0.323
|
2.70
|
Error
|
4
|
0.4397
|
0.1099
|
|
|
8.53
|
Total
|
8
|
5.1567
|
|
|
|
|
3.1.4 Effects of process factors on Flexural strength
The % contribution of significant factors to the flexural strength is reported in ANOVA table 7. For flexural strength, it was observed that, powder size has the highest influence (p = 44.92%), afterword’s by sintering speed (p = 42.09%), sintering temperature (p = 0.68%) and wt. % of foaming agent (p = 0.03%) depicted least significant contributions to flexural strength. The main and interaction plot depicts individuals and their effects on flexural strength, as shown in figure 13.
Table 8. ANOVA results for Flexural Strength (MPa)
Source
|
DOF
|
Adj. SS
|
Adj. MS
|
F-Value
|
P-Value
|
Percentage of contribution
|
A
|
1
|
0.77533
|
0.775334
|
14.64
|
0.019
|
44.92
|
B
|
1
|
0.72659
|
0.726591
|
13.72
|
0.021
|
42.09
|
C
|
1
|
0.01168
|
0.011680
|
0.22
|
0.663
|
0.68
|
D
|
1
|
0.00061
|
0.000613
|
0.01
|
0.920
|
0.03
|
Error
|
4
|
0.21188
|
0.052970
|
|
|
12.27
|
Total
|
8
|
1.72610
|
|
|
|
|
3.2 Statistical interpretation using the Taguchi approach
In the present study, better criteria were applied for all the output properties of AMF to obtain an S/N ratio more significant. As per the considered criteria, the S/N signal-to-noise ratio should possess a higher value to obtain optimum test conditions. The ranking for the input process factors is acquired using its S/N signal-to-noise ratios with four levels for % porosity and compressive, tensile, and flexural strength, as reported in Table 9. The ranks for the input process factors are obtained to establish the relative magnitude of effects based on the delta statistics [37].
Table 9. Responses acquired in S/N ratios
% porosity
|
Compressive strength (MPa)
|
Level
|
A
|
B
|
C
|
D
|
Level
|
A
|
B
|
C
|
D
|
1
|
37.00
|
36.88
|
36.84
|
36.89
|
1
|
18.55
|
19.71
|
20.21
|
19.89
|
2
|
36.99
|
36.87
|
36.85
|
36.84
|
2
|
20.26
|
19.89
|
20.17
|
19.97
|
3
|
36.56
|
36.82
|
36.87
|
36.83
|
3
|
21.43
|
20.65
|
19.86
|
20.38
|
Delta
|
0.44
|
0.06
|
0.03
|
0.06
|
Delta
|
2.89
|
0.94
|
0.35
|
0.49
|
Rank
|
1
|
3
|
4
|
2
|
Rank
|
1
|
2
|
4
|
3
|
Tensile strength (MPa)
|
Flexural strength (MPa)
|
Level
|
A
|
B
|
C
|
D
|
Level
|
A
|
B
|
C
|
D
|
1
|
11.61
|
12.34
|
12.52
|
13.15
|
1
|
12.28
|
12.59
|
13.27
|
13.03
|
2
|
12.40
|
12.69
|
12.91
|
12.68
|
2
|
13.44
|
12.90
|
13.11
|
13.37
|
3
|
14.55
|
13.53
|
13.13
|
12.73
|
3
|
13.70
|
13.92
|
13.04
|
13.02
|
Delta
|
2.93
|
1.19
|
0.61
|
0.47
|
Delta
|
1.42
|
1.33
|
0.23
|
0.35
|
Rank
|
1
|
2
|
3
|
4
|
Rank
|
1
|
2
|
4
|
3
|
3.3 Confirmation tests
In the DOE approach, the final step is the confirmation of experiments. After investigating the optimal test conditions, the confirmation was performed considering the optimum level of factors. The acquired results were eventually compared with the predicted results [42]. Table 10 demonstrates the comparative results obtained using optimal parameters. It has been observed that there was reasonable agreement between the experimental and predicted results. However, an error of 3.20% for % porosity, 5.99% compressive strength, 9.23% tensile strength, and 3.35% flexural strength (S/N ratios) was observed.
Table 10. Confirmation tests
|
Initial parameter combination
|
Prediction
|
Experimentation
|
Improvement in S/N ratio
|
Level
|
A1B1C1D1
|
A1B1C3D1
|
|
% porosity
|
67.45
|
67.74
|
69.91
|
|
SN ratio (dB)
|
36.57
|
36.72
|
37.89
|
3.20
|
|
|
|
|
|
Level
|
A3B3C2D1
|
A3B3C2D3
|
|
Compressive strength (MPa)
|
8.20
|
8.29
|
7.89
|
|
SN ratio (dB)
|
18.22
|
18.43
|
17.54
|
5.99
|
|
|
|
|
|
Level
|
A3B3C2D1
|
A3B3C1D1
|
|
Tensile strength (MPa)
|
3.74
|
3.68
|
4.02
|
|
SN ratio (dB)
|
11.44
|
11.25
|
12.28
|
9.23
|
|
|
|
|
|
Level
|
A3B3C2D1
|
A3B3C1D2
|
|
Flexural strength (MPa)
|
3.80
|
3.81
|
3.94
|
|
SN ratio (dB)
|
11.59
|
11.62
|
12.01
|
3.35
|