Cold gas dynamic spraying of a high temperature Al alloy L. Ajdelsztajn a, * , A. Zu ´n ˜iga a , B. Jodoin b , E.J. Lavernia a a Dept. of Chemical Engineering and Materials Science, University of California, Davis, CA 95616, United States b Dept. of Mechanical Engineering, University of Ottawa, Ontario, Canada K1N 6N5 Received 25 February 2005; accepted in revised form 27 May 2005 Available online 19 July 2005 Abstract The present paper describes a study of the influence of cold spraying on the microstructure, heat treatment response and mechanical behavior of a high temperature 2618 aluminum alloy (Al – Cu – Mg – Fe – Ni) modified with 0.16 wt.% Sc. The microstructure of the starting powder consisted of a network of Al 2 CuMg phase on the grain boundaries of the Al matrix, along with Al 9 FeNi precipitates for atomized powder particles larger than 20 Am, and a cellular solidification structure for particles smaller than 20 Am. The coating after deposition was composed of the same microstructure features as observed in the feedstock powder but highly deformed. The observed overall deformation suggests the occurrence of localized adiabatic shear instability at the particle/particle boundary and adiabatic deformation softening at the powder interior during splat formation. The coating hardness was similar to the one obtained at the peak aged condition (T6). The coating aging response was influenced by the presence of Al 7 FeCu 2 particles that depleted the matrix from Cu, reducing the overall hardness and overcoming the benefits of Sc addition. D 2005 Elsevier B.V. All rights reserved. Keywords: Cold gas dynamic spray; High temperature Al alloys; Coatings 1. Introduction The ever increasing demand to manufacture weight efficient structures that are damage tolerant and can operate at elevated temperatures has fueled the development of novel alloy compositions and radically different processing approaches over the last decades. A case in point is the family of commercial Al alloys, in which the operating temperature is generally limited to temperatures close to ¨ 250 -C. Inspection of the literature on elevated temper- ature Al alloys reveals two important findings. First, adequate elevated thermal stability will only be attained via non-equilibrium microstructures that incorporate, for example, insoluble Fe dispersoids [1]. Second, successful implementation of these materials will strictly depend on the ability to conceive processing strategies that successfully retain these non-equilibrium microstructures. One such strategy, cold gas dynamic spraying, is the topic of the present study. Al–Cu alloys have been extensively used in the past in aerospace, aeronautical and automotive applications due to their high strength, up to intermediate temperatures (¨ 200 -C) [2]. In these alloys, the normal aging sequence after a high temperature solution treatment is as follows [3]: super- saturated solid solutionYGuinier-Preston (GP) zonesY uµYuVYu, where the metastable phases uµ and uV are responsible for the high strength observed in this type of alloys [4]. The addition of alloying elements in Al – Cu alloys (such as Mg or Ag) has also been investigated, resulting in the formation of novel metastable intermetallic phases (such as V Al 2 Cu) [5]. In the case of low Cu, high Mg alloys, the main strengthening phase changes from plate-like uV (metastable form of Al 2 Cu) to rod-shaped SV (metastable form of Al 2 CuMg) [6], giving rise to a more stable system. Further development of alloys with a low Cu/Mg ratio gave rise to the 2618 aluminum alloy (Al – Cu – Mg – Fe – Ni) for intermediate temperatures (¨ 230 -C), where the addition of Fe and Ni (1 wt.% each) promotes the formation of stable Al 9 FeNi 0257-8972/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2005.06.001 * Corresponding author. E-mail address: lajd@ucdavis.edu. (L. Ajdelsztajn). Surface & Coatings Technology 201 (2006) 2109 – 2116 www.elsevier.com/locate/surfcoat