The present paper considers the friction performance of Al-10%SiCp reinforced metal matrix composites against steel for varying tribological test parameters. The composite is prepared by stir-casting process using aluminium alloy LM6 being mixed with 10% silicon carbide by weight. The tribological tests are performed by varying applied load, sliding speed, and time. The friction performance is studied using plate-on-roller configuration in a multitribotester and optimized using Taguchi L27 orthogonal array. Analysis of variance (ANOVA) is performed to observe the significance of test parameters and their interactions on friction performance. It is observed that normal load and the interaction between normal load and speed influence the friction behaviour, significantly. The wear tracks are analyzed with the help of scanning electron microscopy.
Particle reinforced composites are recognized as a light weight material having enhanced mechanical and tribological properties than the constituent materials. The MMC (metal matrix composite) materials attain the toughness of the alloy matrix and hardness, stiffness, and strength of the reinforcement. Researchers [
The increasing use of composite materials in the automobile and aeronautics fields is due to good friction and wear properties. In aeronautics, it is used for manufacturing of rotor blades due to increased creep resistance. The aluminium composites exhibit lower friction coefficient than their base alloys [
For the present experimental study LM6 aluminium alloy is used as base metal and silicon carbide particle (SiCp) is used as reinforcement (10% by weight). The composite is prepared by stir-casting process in an electric melting furnace. The tribological tests are carried out on Al-10%SiCp for testing the friction property of the material. The result data are analyzed by Taguchi method. Furthermore, a statistical analysis of variance (ANOVA) is performed to find the statistical significance of tribological test parameters. Finally, a confirmation test is carried out to verify the optimal process parameters obtained from the parameter design. The microstructure study is done with the help of SEM to judge the wear mode of the material.
The Taguchi method [
For the fabrication of the composite, aluminium alloy, that is, LM6, is used as matrix metal that has been reinforced with 10 wt% of SiC particles of 400 mesh size. The chemical composition of the matrix material (LM6) is given in Table
Chemical composition of LM6.
Elements | Si | Cu | Mg | Fe | Mn | Ni | Zn | Pb | Sb | Ti | Al |
---|---|---|---|---|---|---|---|---|---|---|---|
Percentage (%) | 10–13.0 | 0.1 | 0.1 | 0.6 | 0.5 | 0.1 | 0.1 | 0.1 | 0.05 | 0.2 | Remaining |
Design of experiments (DOE) technique introduced by Fisher [
Design factors with levels
Design factors | Unit | Levels | ||
---|---|---|---|---|
1 | 2 | 3 | ||
Load ( |
N | 50 | 75i | 100 |
Speed ( |
RPM | 180 | 200i | 220 |
Time ( |
MIN | 20 | 30i | 40 |
i: initial condition.
DOE basically refers to the process of planning, designing, and analyzing the experiment so that valid and objective conclusion can be drawn effectively and efficiently. Based on Taguchi method an orthogonal array (OA) is considered to reduce the number of experiments required to determine the optimal friction for Al-10%SiCp metal matrix composite. An OA provides the shortest possible matrix of combinations in which all the parameters are varied to consider their direct effect as well as interactions simultaneously Taguchi has tabulated several standard OAs. In this investigation, a L27 OA which has 27 rows corresponding to the number of tests and 26 degrees of freedom (DOFs) with 13 columns at three levels is chosen. To check the DOFs in the experimental design, for the three level test, the three main factors take 6 [
L27 orthogonal array with design factors.
Column | |||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Trial no. | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 |
( |
( |
( |
( |
( |
( |
( |
( |
— | — | ( |
— | — | |
1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
2 | 1 | 1 | 1 | 1 | 2 | 2 | 2 | 2 | 2 | 2 | 2 | 2 | 2 |
3 | 1 | 1 | 1 | 1 | 3 | 3 | 3 | 3 | 3 | 3 | 3 | 3 | 3 |
4 | 1 | 2 | 2 | 2 | 1 | 1 | 1 | 2 | 2 | 2 | 3 | 3 | 3 |
5 | 1 | 2 | 2 | 2 | 2 | 2 | 2 | 3 | 3 | 3 | 1 | 1 | 1 |
6 | 1 | 2 | 2 | 2 | 3 | 3 | 3 | 1 | 1 | 1 | 2 | 2 | 2 |
7 | 1 | 3 | 3 | 3 | 1 | 1 | 1 | 3 | 3 | 3 | 2 | 2 | 2 |
8 | 1 | 3 | 3 | 3 | 2 | 2 | 2 | 1 | 1 | 1 | 3 | 3 | 3 |
9 | 1 | 3 | 3 | 3 | 3 | 3 | 3 | 2 | 2 | 2 | 1 | 1 | 1 |
10 | 2 | 1 | 2 | 3 | 1 | 2 | 3 | 1 | 2 | 3 | 1 | 2 | 3 |
11 | 2 | 1 | 2 | 3 | 2 | 3 | 1 | 2 | 3 | 1 | 2 | 3 | 1 |
12 | 2 | 1 | 2 | 3 | 3 | 1 | 2 | 3 | 1 | 2 | 3 | 1 | 2 |
13 | 2 | 2 | 3 | 1 | 1 | 2 | 3 | 2 | 3 | 1 | 3 | 1 | 2 |
14 | 2 | 2 | 3 | 1 | 2 | 3 | 1 | 3 | 1 | 2 | 1 | 2 | 3 |
15 | 2 | 2 | 3 | 1 | 3 | 1 | 2 | 1 | 2 | 3 | 2 | 3 | 1 |
16 | 2 | 3 | 1 | 2 | 1 | 2 | 3 | 3 | 1 | 2 | 2 | 3 | 1 |
17 | 2 | 3 | 1 | 2 | 2 | 3 | 1 | 1 | 2 | 3 | 3 | 1 | 2 |
18 | 2 | 3 | 1 | 2 | 3 | 1 | 2 | 2 | 3 | 1 | 1 | 2 | 3 |
19 | 3 | 1 | 3 | 2 | 1 | 3 | 2 | 1 | 3 | 2 | 1 | 3 | 2 |
20 | 3 | 1 | 3 | 2 | 2 | 1 | 3 | 2 | 1 | 3 | 2 | 1 | 3 |
21 | 3 | 1 | 3 | 2 | 3 | 2 | 1 | 3 | 2 | 1 | 3 | 2 | 1 |
22 | 3 | 2 | 1 | 3 | 1 | 3 | 2 | 2 | 1 | 3 | 3 | 2 | 1 |
23 | 3 | 2 | 1 | 3 | 2 | 1 | 3 | 3 | 2 | 1 | 1 | 3 | 2 |
24 | 3 | 2 | 1 | 3 | 3 | 2 | 1 | 1 | 3 | 2 | 2 | 1 | 3 |
25 | 3 | 3 | 2 | 1 | 1 | 3 | 2 | 3 | 2 | 1 | 2 | 1 | 3 |
26 | 3 | 3 | 2 | 1 | 2 | 1 | 3 | 1 | 3 | 2 | 3 | 2 | 1 |
27 | 3 | 3 | 2 | 1 | 3 | 2 | 1 | 2 | 1 | 3 | 1 | 3 | 2 |
The tribological tests are carried out in a plate on roller multitribotester TR25 (Ducom, India) (Figure
Schematic diagram of Multitribotester.
After friction tests, scanning electron microscopy (SEM) is used to evaluate the microstructure of the specimens. The microstructure study is conducted to know the nature of the wear tracks. A scanning electron microscope (JEOL, JSM-6360) is used for the microstructure study of the material.
The aim of the present study is to minimize friction of Al-10%SiCp by optimizing the tribo-testing parameters with the help of Taguchi method. The influence of tribological testing parameters like applied load, sliding speed, and sliding duration together with their interactions on the friction behaviour of Al-10%SiCp is studied. Since the study is related to friction, coefficient of friction is taken as system response. Accordingly, the effect of the tribo-testing conditions on the friction behaviour of Al-10% SiCp is studied.
The desirable factor levels are calculated by simple average of the results. This traditional method is not able to capture the variability of the results within the trial condition. Thus the
Friction test results.
Trial no. | COF | S/N ratio |
---|---|---|
1 | 0.353 | 9.0445 |
2 | 0.356 | 8.9710 |
3 | 0.344 | 9.2688 |
4 | 0.392 | 8.1343 |
5 | 0.371 | 8.6125 |
6 | 0.383 | 8.3360 |
7 | 0.350 | 9.1186 |
8 | 0.369 | 8.6595 |
9 | 0.394 | 8.0901 |
10 | 0.314 | 10.061 |
11 | 0.322 | 9.8429 |
12 | 0.328 | 9.6825 |
13 | 0.331 | 9.6034 |
14 | 0.348 | 9.1684 |
15 | 0.366 | 8.7304 |
16 | 0.399 | 7.9805 |
17 | 0.386 | 8.2683 |
18 | 0.395 | 8.0681 |
19 | 0.258 | 11.768 |
20 | 0.318 | 9.9515 |
21 | 0.333 | 9.5511 |
22 | 0.271 | 11.341 |
23 | 0.320 | 9.8970 |
24 | 0.284 | 10.934 |
25 | 0.275 | 11.213 |
26 | 0.308 | 10.229 |
27 | 0.284 | 10.934 |
Response table for friction coefficient.
Level | Load | Speed | Time |
---|---|---|---|
1 | 8.693 | 9.793 | 9.807 |
2 | 9.045 | 9.417 | 9.289 |
3 | 10.646 | 9.173 | 9.288 |
Rank | 1 | 2 | 3 |
Delta | 1.954 | 0.620 | 0.519 |
Total mean S/N ratio = 9.461 dB.
Main effects plot.
Interaction plots: (a) load versus speed, (b) load versus time, and (c) speed versus time.
ANOVA is a statistical technique which can provide some important conclusions based on analysis of the experimental data. This method is very useful for revealing the level of significance of the influence of factor(s) or interaction of factors on a particular response. It separates the total variability of the response into contributions of each of the factors and the error. Using Minitab [
ANOVA table for coefficient of friction.
Source | DF | SS | MS |
|
Contribution (%) |
---|---|---|---|---|---|
|
2 | 19.51 | 9.76 | 39.61# | 63.20 |
|
2 | 1.76 | 0.86 | 3.56* | 5.69 |
|
2 | 1.61 | 0.81 | 3.28* | 5.23 |
|
4 | 4.01 | 1.01 | 4.06 |
12.96 |
|
4 | 1.83 | 0.46 | 1.86 | 5.94 |
|
4 | 0.19 | 0.05 | 0.19 | 0.60 |
Error | 8 | 1.98 | 0.25 | 6.38 | |
| |||||
Total | 26 | 30.89 | 100 |
Significant parameters and interactions (#
After the optimal level of testing parameters have been found, it is necessary that verification tests are carried out in order to evaluate the accuracy of the analysis and to validate the experimental results. The estimated
Table
Confirmation result table.
|
Initial parameter | Optimal parameter | |
---|---|---|---|
Predicted | Experimental | ||
Level | L2S2T2 | L3S1T1 | L3S1T1 |
COF | 0.348 | 0.258 | |
S/N ratio (dB) | 9.1684 | 11.3243 | 11.7676 |
Improvement of S/N ratio = 2.5992 dB.
Figure
SEM image of worn surface of Al-10%SiCp composite.
In the present study, the influence of three factors, That is, applied load, sliding speed and time on the friction behaviour of Al-SiCp composite is studied. Some other factors like heat treatment, temperature, volume fraction of reinforcement, and so forth are considered to be constant in this investigation. In future studies,an attempt will be made to evaluate the effect of these factors on the friction behaviour of the composite.
The friction performance of Al-10%SiCp reinforced metal matrix composites against steel is studied for varying tribological test parameters. The optimal tribological testing combination for minimum friction is found to be L3S1T1, that is, the highest level of normal load and lowest levels of speed and time. All the factors applied load (