The Cold Spray (CS) process is an emerging and promising coating technology that can produce conventional and nanocrystalline coatings. In CS, solid particles are accelerated above a critical velocity in a supersonic gas flow. Upon impact on a substrate, the particles deform plastically and bond to the substrate to form a coating. CS aluminum coatings have demonstrated an increased surface hardness and improved corrosion resistance. Although the CS process is mainly governed by the particle impact velocity, other process parameters, that do not change the particle impact velocity, might influence the coatings quality. Accordingly, it becomes important to identify and evaluate the effects of these parameters. The influence of four spray parameters including substrate surface conditions, powder feed rate, spray distance and traverse speed on the mechanical properties of CS aluminum alloy coatings will be examined. Coatings were produced at a constant particle velocity and experiments were conducted using a Taguchi fractional factorial design parametric study. The coatings microstructures are observed and the coatings are characterized by adhesive strength tests, hardness tests, porosity, and thickness. In particular, this presentation describes the testing and the particle in-flight diagnostic methods, and attempts to correlate the mechanical properties of the coatings to the process parameters.