Figure 4
The microscopy for the surface topography of the friction pairs of (a) Al-Al under 5 N; (b) Al-Al under 30 N; (c) Al-Al under 50 N; (d) Al-Cu under 5 N; (e) Al-Cu under 30 N; (f) Al-Cu under 50 N. (The lighter, brighter phase is Al, whereas the darker, more yellowish phase is Cu). (Note: All pictures are taken along the reciprocating motion direction of the friction pairs).
