Residual Stress Induced by Cold Spray Coating on Magnesium Substrate

Cold spray is a solid-state coating process, at a relatively low gas temperature, that uses a high-speed gas flow to accelerate solid micrometer size particles (in powder form) towards a substrate where they plastically deform and consolidate upon impact. Flat specimens were machined from an AZ31B extrusion piece in the longitudinal direction. The samples were grit blasted and then cold sprayed with aluminum 1100 particles of an average diameter of 40μm, with a velocity of 400m/s. The residual stresses in coated and uncoated samples were then measured using XRD method. It is shown that a residual compressive stress of the order of 25MPa is induced at the surface of the substrate due to cold spray coating. The process of spraying was modeled using ANSYS finite element software. The generalized Hill’s anisotropic material model which allows yield asymmetry and anisotropic behavior was utilized. All material parameters were obtained from tests performed on the substrate. The results obtained from modeling the impact of Al particles on Mg substrate was compared with measured stresses. The trend of residual stress distribution at and under the substrate’s surface agrees with the measurements. The maximum value of stress and its location as revealed by test and simulation agree very well.