Mg and Al-based alloys have gained importance in the automotive, aviation, and more recently oil and gas industry due to their high strength-to-weight ratio, high stiffness, and commercial availability. However, their limited erosion and corrosion resistance is a concern, especially for oil and gas application with aggressive environment: corrosive fluid laden with 2 - 5 vol % of sand, flowing at up to 70 - 80 mph. In the present study, five types of metal and cemented carbide coatings were deposited on a proprietary Mg-based composite substrate with the aim to improve its erosion and corrosion resistance. The microstructure and phase constituents were examined using scanning electron microscope (SEM including EDAX) and X-ray diffraction. The erosion performances were investigated by water + 2% sand slurry as a function of flow rate and jet-substrate angle. The performance of the coatings was correlated to their microstructure.