The effect of process temperature and powder composition on microstructure and mechanical characteristics of low-pressure cold spraying aluminum-based coatings

Abstract

The effect of operating gas temperature and powder type on microstructure and mechanical characteristics of cold spraying coatings deposited on EZ33A-T5 magnesium alloy was studied. Three aluminum-based cold spraying powder mixtures Al + Zn, Al + Al2O3 and Al + Zn + Al2O3 were used for the investigation. Deposition was performed using D423 low-pressure cold spray system at operating gas pressure of 1.0 MPa and different temperatures –300 °C, 450 °C, and 600 °C. The coatings microstructure was investigated with optical and scanning electron microscopy. Mechanical properties of the coatings were characterized through standard test methods for adhesion and cohesion strength, and standard test methods for Vickers hardness of thermal spray coatings. The results demonstrate that with increasing initial gas temperature at spraying nozzle inlet from 300 °C to 600 °C, an increase in the porosity of the coatings of all investigated powder mixtures can be observed. Microstructure characterization showed an increase in porosity from 2.3% to 4.1% for Al + Zn powder mixture, from 2.1% to 3.5% for Al + Al2O3 powder mixture, and from 2.5% to 5.6% for Al + Zn + Al2O3 powder mixture. The minimum porosity was obtained at 450 °C for all investigated powder mixtures. Adhesion and cohesion strength and microhardness of coatings were reach their maximum value at 450 °C. The best performance was obtained for Al + Al2O3 powder mixture: coating adhesion—31.9 MPa (was limited by the bonding strength of the glue), cohesion—93.5 MPa, microhardness—81 HV0.15. The influence of Al2O3 particles in the powder mixture on the above-mentioned parameters was also established. The results show that the presence of ceramic particles in powder mixtures can positively effect porosity level and mechanical characteristics.