EXCIMER-LASER TREATMENT FOR ALUMINUM-ALLOY MECHANICAL PROPERTY ENHANCEMENT

An excimer laser beam is focused (1-3 J cm(2)) on to an aluminium allo y (AlSi7Mg) surface target in a nitrogen atmosphere (760 Torr). A nitr ide layer (5 mm(2) area per laser spot) is obtained by nitrogen diffus ion in the bulk with a depth of several micrometres during the induced laser-plasma rime interaction on the surface. For chemical, structura l and tribological analyses, 1 x 1 cm(2) samples are processed by scan ning the laser beam on the surface, either by locating the laser-plasm a spots side by side or by overlapping them. Different experimental co nditions are investigated (laser fluence, laser pulse number, overlapp ing rate of laser-plasma spots), and then various analysis such as NRA , XRD, GIXD, SEM, EDS are performed. When a step-by-step process is us ed, the nitrogen concentration appears to be inhomogeneous depending o n the surface location, and the surface toughness is too high for furt her applications. Nevertheless, the overlapping process yields homogen eous chemical composition layers with smooth surfaces. Tests are perfo rmed to characterise the friction behaviour of the treated surface und er fretting conditions. and tribological results clearly indicate the best experimental conditions to be used for the enhancement of mechani cal properties. (C) 1998 Elsevier Science S.A.