Heat treatment of cold-sprayed C355 Al for repair: microstructure and mechanical properties

Cold gas dynamic spraying of commercially pure aluminum is widely used for dimensional repair in the aerospace sector as it is capable of producing oxide-free deposits of hundreds of micrometer thickness with strong bonding to the substrate, based on adhesive pull-off tests, and often with enhanced hardness compared to the powder prior to spraying. There is significant interest in extending this application to structural, load-bearing repairs. Particularly, in the case of high-strength aluminum alloys, cold spray deposits can exhibit high levels of porosity and microcracks, leading to mechanical properties that are inadequate for most load-bearing applications. Here, heat treatment was investigated as a potential means of improving the properties of cold-sprayed coatings from Al alloy C355. Coatings produced with process conditions of 500 °C and 60 bar were heat-treated at 175, 200, 225, 250 °C for 4 h in air, and the evolution of the microstructure and microhardness was analyzed. Heat treatment at 225 and 250 °C revealed a decreased porosity (~ 0.14% and 0.02%, respectively) with the former yielding slightly reduced hardness (105 versus 130 HV0.05 as-sprayed). Compressive residual stress levels were approximately halved at all depths into the coating after heat treatment, and tensile testing showed an improvement in ductility

Effect of particle size, morphology, and hardness on cold gas dynamic sprayed aluminum alloy coatings

This work describes recent progress in Cold Gas Dynamic Spraying process of conventional and nanocrystalline 2618 (Al-Cu-Mg-Fe-Ni) aluminum alloy containing Sc. As-atomized and cryomilled 2618 + Sc aluminum powders were sieved in two ranges of particle size (below 25 mu m and between 25 and 38 mu m), and sprayed onto aluminum substrates. The mechanical behavior of the powders and the coatings was studied using the nanoindentation technique, while the microstructure was analyzed using scanning and transmission electron microscopy. The influence of the powder microstructure, morphology and behavior during deposition on the coating properties was analyzed. It was concluded that the hard cryomilled particles do not experience extensive plastic deformation, and therefore failed to form a coating as dense as those produced using the gas-atomized spherical powder, despite the fact that the irregular shape cryomilled particles presented higher flight and impact velocities than the gas-atomized spherical particles. It was also observed that the influence of the particle morphology on the particle velocities is more pronounced for the larger particle size range (between 25 and 38 gm)