The cold spray process is an emerging and promising coating technology that can produce nano-crystalline, amorphous and crystalline coatings.  To this day, few studies have looked in details at the relationship between the particle velocities and the coating’s physical and mechanical properties.  As the development period of the cold spray technique continues, it becomes important to examine and evaluate this relationship for optimization purposes. This study is part of an on-going investigation that looks at the correlation between  the spraying parameters and the coating properties such as thickness, hardness, porosity and bond strength.  In particular, this paper examines the relationship between the particle in-flight velocity and the microstructure and adhesion strength of cold spray aluminum alloy coatings.  An in-flight particle diagnostic system is used to measure the particle velocities.  The coatings microstructures are observed and the coatings are subjected to adhesive strength testing according to standard mechanical testing methods.  This paper describes the diagnostic system implementation, the testing method and the effects of the particle velocities on the coating microstructure and bond strength.