**4. Conclusion**

324 Recent Trends in Processing and Degradation of Aluminium Alloys

the A6092 data was better represented by an exponential fit. Since this data did not fit the same trend as the other alloys, the experiment was repeated and measurements re-taken, but with essentially the same result. Thus, the difference in behaviour of this alloy appears to be reproducible. Interestingly, the two alloys where the specific wear rate was relatively insensitive to MML thickness also exhibited MML with the least Fe content (Table 2) and the most homogeneous structure. Conversely, the A6092 exhibited the highest Fe content, the most heterogeneous structure and the greatest influence on the specific wear rate. However, the thickness of the MML cannot explain the dramatic drop in specific wear rate with load observed for the A3004 alloy (Fig. 4b). The thickness of the MML is only one of several potential ways in which the MML can affect wear rate. Clearly for Al/M2 system, the mechanical properties of the MML (in particular hardness and fracture stress) and its

**2124 3004 5056 6092** 

**42N 140N 23N 140N 23N 140N 42N 140N** 

*Mg* 1.8 ± 0.3 2.0 ± 0.4 - - 6.8 ± 0.5 6.8 ± 1.1 1.0 ± 0.1 1.7 ± 0.3

*Al* 85.3 ± 1.9 73.4 ± 5.9 94.9 ± 9.2 95.3 ± 5.6 80.5 ± 7.8 86.8 ± 7.7 61.8 ± 7.6 79.9 ± 5.8

*Si* 1.0 ± 0.5 - 0.7 ± 0.2 0.8 ± 0.3 1.0 ± 0.4 0.4 ± 0.1 1.6 ± 0.4 1.1 ± 0.3

*Fe* 6.6 ± 1.5 19.1 ± 4.8 1.9 ± 1.5 2.7 ± 1.8 11.7 ± 5.4 6.0 ± 5.5 34.5 ± 7.8 15.9 ± 7.4

*Cu* 4.3 ± 0.6 4.1 ± 1.1 - - - - 0.8 ± 0.2 1.3 ± 0.6

Table 2. Average quantitative EDS analysis on MML of Al-alloys against M2 (Ghazali, 2005) In Al/M2 system, the A6092 exhibited the thickest MML and the highest Fe content. Since this was not replicated by the A5056, rather the reverse, it is clear that it is not the Mg content of the A6092 that promotes the formation of a thick MML. Thus, these results imply that stronger adhesion and transfer from the counterface is promoted by the Si in the alloy, while a high Mg content in the Al-alloy reduces adhesion. Similarly, the presence of Cu in the A2124 also appears to have promoted stronger adhesion than an equivalent amount of Mg, although the Cu was not as potent as the Si. The Mn in the A3004 also promoted a relatively thick MML, but one that was more homogeneous than for the A6092. The solubility of these elements in α-Al is in the order Si, Mn, Cu, Mg, which roughly approximates to the thickness of the MML formed. Thus, the observations are in-line with the Archard theory of adhesive wear, as might be expected. However, the level of alloy additions are small (e.g. Si) and it is surprising that the effect was as strong as observed. Thus, the wear performance is largely determined by the properties of the

The atmosphere under an unlubricated wear process can strongly influence sliding wear rates with oxygen content and humidity being probably one of the important factors. In the

*Mn* 1.1 ± 0.1 1.4 ± 0.5 2.5 ± 1.8 1.1 ± 0.2 - - 0.3 ± 0.1 -

adhesion to the substrate are contributing factors.

**Element** 

MML.

**3.5 Effect of other variables** 

In general, the dry sliding of Al/M2 systems showed the following responses as a result of repeated stress and frictional heat cycle:


Effects of Dry Sliding Wear of Wrought Al-Alloys on Mechanical Mixed Layers (MML) 327

How, H.C., and Baker, T.N. (1997). Dry sliding wear behaviour of Saffil-reinforced AA6061

Jiang, J.Q., and Tan, R.S. (1996). Dry sliding wear of an alumina short fibre reinforced Al-Si

Kuhlmann-Wilsdorf, D. (1987). Demystifying flash temperatures I. Analytical expressions

Kuo, S.M., and Rigney, D.A. (1992). Sliding Behavior of Aluminum. *Mat. Sci. Tech*., Vol. 157,

Leonard, A.J., Perrin, C., and Rainforth, W.M. (1997). Microstructural changes induced by

Li, X.Y., and Tandon, K.N. (1999). Mechanical mixing induced by sliding wear of an Al Si

Maupin H.E., Wilson R.D., Hawk J.A. An abrasive wear study of ordered Fe3Al. *Wear*, Vol.

Maupin, H. E. Wilson, R. D. and Hawk, J. A. (1993). Wear deformation of ordered Fe-Al

Perrin, C. and Rainforth, W.M. (1995). The effect of alumina fibre reinforcement on the wear

Ravikiran, A., Nagarajan, V.S., and Biswas, S.K., Pramila Bai, B.N. (1995). Effect of. Speed

Rice S.L., Nowothy, H., and Wayne, S.F. (1981-1982). Characteristics of metallic subsurface

Rigney, D.A., ed. 1981, in Fundamentals of Friction and Wear of Materials: Am. Soc. for

Rigney, D.A., Chen, L.H., Naylor, M.G., and Rosenfield, A. (1984). Wear processes in sliding

Rigney, D.A. (1998). Large Strains Associated with Sliding Contact of. Metals. *Mater. Res.* 

Rittner, M. (2000). *Metal matrix composites in 21st. century: markets and opportunities*, BCC, Inc.,

Suh N.P., Jahanmir, S., Flemming, J.R., Pamies-Teixeira, J.J., Saka, N. (1977). Overview of the

Wang A., Rack H.J. (1991). Abrasive wear of silicon carbide particulate—and whiskerreinforced 7091 aluminum matrix composites. *Wear*, Vol. 146, pp. 337-348.

(2002). High-resolution observations of friction-induced oxide and its Interaction

and Pressure on Dry Sliding Interactions of Alumina against Steel. *J. Am. Ceram.* 

dry sliding wear of a A357/SiC metal matrix composite. *Mater. Sci. Tech.*, Vol. 13,

composites. *Wear*, Vol. 210, pp. 263-272.

pp. 131-143.

No. 1, pp. 41-48.

159, pp. 241-247.

alloy against steel. *Wear*, Vol. 195, No. 1-2, pp. 106-111.

alloy against M2 steel. *Wear*, Vol. 225-229, pp. 640-648

intermetallic alloys. *Wear*, Vol. 162-164, pp. 432-440.

Pollack, H.W. (1977). *Mat. Sci. and Met.*, 2nd edn., Virginia, Prentice Hall.

with the Worn Surface. *Tribol. Int*., Vol. 35, pp. 731–748.

zones in sliding and impact wear. *Wear*, Vol. 74, pp. 131 -142

Suh, N.P. (1973). The delamination theory of wear. *Wear,* Vol. 25, pp. 111-124.

*Soc.*, Vol. 78, No. 2, pp. 356-364.

systems. *Wear*, Vol. 100, pp. 195-219.

Sheu, C.Y. Lin, S.J. (1997). *Journal of materials science*, 32 pp. 1741.

Delamination Theory of Wear. *Wear*, pp. 44, 1-16.

Metals, Metals Park, Ohio.

*Innovat.,* Vol. 1, pp 231-234.

Norwalk, C.T.

of an Al-4.3%Cu alloy. Wear, Vol. 181-183, No. 12, pp. 312-324.

Polmear, I.J. (1989). *Metallurgy of the Light Metals*, 2nd edn., Edward Arnold. New York. Rainforth, W.M., Leonard, A.J., Perrin, C., Bedolla-Jacuinde, A.,. Wang, Y., Jones, H., Luo, Q.

Johnson, K.L. (1985). *Contact Mechanics*, Cambridge University Press, Cambridge.

based on a simple model. *Mat. Sci. Eng*., Vol. 93, pp. 107-118.

