Cold Spray Repair of Magnesium Gearbox Castings

Cold spray is an ideal process for the consolidation of aluminum protective coatings on magnesium alloy components such as helicopter gear box housings due to the low deposition temperatures, high bond strengths, and minimal porosity. The objective of this study was to examine the microstructural, mechanical, and corrosion properties of Commercially Pure (CP) aluminum and 6061 aluminum alloy cold spray coatings deposited on ZE41A-T5, AZ91C-T6, and EV31-T6 magnesium alloy substrates. The cold spray process uses a converging-diverging nozzle to accelerate a carrier gas containing non-molten particles of the coating species upon the substrate.  Ballistic impingement results in bonding and subsequent coating build up.  A few of the specific coating properties evaluated during this study include density, adhesion (ASTM C 633), residual stress, tensile tests, R.R. Moore rotating beam fatigue, and variety of corrosion tests including galvanic (ASTM G 71) and salt fog (ASTM B 117).  Additionally, implementation procedures for specific gearbox components were also developed as part of this effort.