Wear 253 (2002) 1077–1085 Mechanical characterisation of laser surface alloyed aluminium–copper systems L. Dubourg a,b,∗ , H. Pelletier b , D. Vaissiere c , F. Hlawka b , A. Cornet b a IREPA LASER, Parc d’Innovation, Pˆ ole API, 67400 Illkirch, France b Laboratoire d’Ingénierie des Surfaces de Strasbourg, ENSAIS, 24 bd de la Victoire, 67000 Strasbourg, France c STIL, Le Mercure C, 80 Rue Charles Duchesne, 13851 Aix en Provence Cedex 3, France Received 23 April 2002; received in revised form 17 July 2002; accepted 17 July 2002 Abstract Additional elements (copper and aluminium) were pre-placed on the aluminium surface and laser alloyed. This pre-placed layer technique gave excellent results concerning micro-hardness, microstructure homogeneity and porosity elimination. The obtained Al–Cu alloys were homogeneous and the micro-hardness varied from 60 to 250 HV 0.2 for 6–40 wt.% Cu. Nano-indentation measurements showed an increase in elastic modulus and particularly in plasticity index. All of these measurements predicted an improved wear behaviour of these coatings com- pared with pure aluminium. A pin-on-disk-type device confirmed the improvement of mechanical properties. In this case, the mass loss can decrease by a factor of 15 between a virginal specimen and a 40 wt.% Cu alloy. In addition, a transition of damage mechanism from a severe wear to a mild wear was observed as the copper ratio of the alloy increased. Wear tracks became homogeneous and wear rate was decreased. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Aluminium; Laser alloying; Nano-indentation; Pin-on-disk-type test 1. Introduction Aluminium alloys offer important advantages on con- struction material, notably by their specific weight, their corrosion resistance and their good thermal conductivity. However, they have poor tribological characteristics: this drawback can be corrected with a laser surface treatment, which does not affect the global properties of the bulk material. Laser alloying consists in melting the aluminium surface while adding another element. This process can be carried out in different ways: pre-placed layer by electrol- ysis [1], by application of a binder [2] or powder [3], or by direct powder injection in the melted pool [4,5]. By means of these processes, several authors used the precipitation of an intermetallic phase with aluminium in order to enhance mechanical characteristics. The elements mainly studied are chromium [5,6], copper [7], nickel [1,3], iron [8] and molyb- denum [9]. The present work deals with aluminium laser alloying with a copper powder pre-placed layer on the spec- imen surface using a binder. The motion of the sample under the laser beam generates a track (see Fig. 1). Convective ∗ Corresponding author. Present address: IREPA LASER, Parc d’Innovation, Pˆ ole API, 67400 Illkirch, France. Tel.: +33-3-88-65-54-00; fax: +33-3-88-65-54-01. E-mail address: ld@irepa.u-strasbg.fr (L. Dubourg). flows, generated by a temperature gradient between the centre of the beam and the sides of the melted pool, ensure the incorporation of the powder and the homogeneity of this surface alloy [10]. In particular, this study presents the me- chanical characterisation of Al–Cu laser alloying. Effects of annealing temperature upon the microstructure and upon the micro-hardness are investigated. In addition to the elastic modulus, the plasticity index and the wear behaviour also are studied as a function of the Cu ratio in the Al–Cu alloys. 2. Experimental set-up 2.1. Laser parameters and component set-up Surface treatments were carried out with a continuous CO 2 laser (Rofin Sinar 5000) of 10.6 m wavelength and energy spatial distribution of TEM 20 type. The selected parameters were as follows: 4000 W laser power on the workpiece, 4.2 × 10 -3 ms -1 scanning speed (see Fig. 1), 4 mm beam diameter on the substrate and 150 ◦ C sample preheating. In order to prevent oxidation of melted pool, the interaction zone was protected with an inert gas at a pressure of 1 bar composed of Ar (flow rate of 8.3 × 10 -2 ls -1 ) and of He (flow rate of 16.7 × 10 -2 ls -1 ). The angle between 0043-1648/02/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved. PII:S0043-1648(02)00218-1