Cold spraying of Al-5Si/Al2O3 composite coatings on AZ31 Mg alloy: Microstructure, adhesion strength, and tribological properties

To improve the wear resistance of commercial AZ31 Mg alloy, two types of dense and thick composite coatings were prepared on AZ31 Mg alloy by means of cold-spray technology. For this purpose, Al2O3 particles with different morphology (round and irregular) were separately added to the Al5Si feedstock. The morphological effects of Al2O3 on the microstructure, adhesion strength, hardness, and tribological properties of the coatings were comprehensively studied. Microstructural features of the coatings were examined by means of optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and electron backscatter diffraction (EBSD). The analysis reveals that most of the grains in both coatings are ultrafine, and approximately half of the total grain boundary length is composed of low-angle grain boundaries. Wear, hardness, and pull-off tests showed that both types of Al2O3 particles have a positive impact on porosity, adhesion, hardness, and wear resistance of the composite coatings. Compared to round Al2O3, irregular Al2O3 particles exhibit better retention in the coating, thereby resulting in a higher hardness and wear resistance.