Micro-forging effect in cold sprayed Al6061/Al7050 coatings

For cost efficient and sustainable cold spray repair of high-strength Al6061 parts, nitrogen is prefered as process gas over costly and exhaustable helium. However, adhesive and cohesive coating properties by using nitrogen are often insufficient. Microforging by in-situ shot peening of cold sprayed coatings is a viable method for achieving better coating qualities with respect to low porosity and high tensile strength. However, the shot peening particles – often other materials like stainless steel or ceramics – are prone for getting embedded into the coating, there as defects compromising properties and risking corrosion. In order to avoid embedding of dissimilar particles, the present study investigates effects of microforging of Al6061 coatings by using high strength Al7050 (80-300µm) powder as peening material. The window of deposition is adjusted for optimum deposition of the smaller Al6061 powder feedstock, whereas the larger Al7050 particles are supposed to rebound and act for peening of the coating without depositing. Deposits processed with and without larger particles for shot peening are investigated with respect to coating microstructures, adhesion and cohesion. Despite some embedded larger particles, the results demonstrate improved coating properties by in-situ peening and promise advantages for aviatiton repair by cold spraying of Al alloys.