Effects of dust and salt particles on the formation and spreading of micro-droplets on AZ91 magnesium alloy

The effects of dust and salt particles on the formation and spreading of micro-droplets on as-cast AZ91 magnesium alloy in an atmosphere of water vapor were investigated using an environmental scanning electron microscope (ESEM). The in situ observations results indicated that both dust particle and AlMn phase stimulated the formation and spreading of micro-droplets, but had few influences on the spreading of water film; salt particle accelerated the formation and spreading of micro-droplets, and the spreading of water film. The generalized form for the spreading kinetics of micro-droplets and water film was D = Atn with D representing the diameter for micro-droplet and the spreading distance for water film, A the formation ability constant of micro-droplet, n the spreading exponent (0 < n < 0.5 for micro-droplet, n > 0.5 for water film). Micro-droplet preferentially formed at the position with a high A value, and the driving force of the spreading of micro-droplets and water film was concentration gradient.