Effect of zirconia secondary peening on the microstructure and mechanical behavior of Al6061 cold spray coatings

Abstract

Cold spray technology is commonly used to repair metallic components with limited temperature influence on the original component. However, for many commercial alloys, such as Al6061, it is still challenging to achieve dense deposits by using low-priced nitrogen gas. The objective of this work was to investigate the effect of secondary peening with zirconia (ZrO2) ceramic beads on the microstructure and mechanical properties of the Al6061 cold spray coatings. Al6061 spherical powder with an average size of 20 μm coupled with zirconia beads of ~210 μm were deposited onto Al6061-T6 substrates using N2 as the carrier gas. The microstructure and mechanical properties of coatings were compared with coatings produced using He and N2 process gases. Microstructural characterization was performed using optical and scanning electron microscopy. Coatings produced with He process gas resulted in lowest porosity and with better mechanical properties compared to the coatings produced using N2 and N2 along with ZrO2. The use of ZrO2 along with N2 process gas resulted in ~15% increase in microhardness, ~680% increase in adhesion strength, ~28% reduction in porosity, and ~34% increase in tensile strengths in the coatings when compared with the coatings produced using N2 process gas only. However, both coatings produced using N2 and N2 coupled with ZrO2 exhibited brittle behavior with no appreciable ductility. Even with this limitation, using ZrO2 as a secondary peening media could provide a cheaper alternative to using He gas for certain cold spray applications where a higher hardness and good adhesion strengths are needed.