In order to understand the influence of different atmospheres on the ignition-proof behavior of spraying deposited magnesium alloy

the morphology

structure and the ignition-proof mechanism of the Mg-5Ca alloy surface film formed under different atmospheres were observed.The results indicate that

after heated at 740 ℃ for 2 h

the surface film formed under commercial nitrogen atmosphere（99.5%）on the alloy exhibits smooth and continuous

while under high-purity nitrogen atmosphere（99.995%）

the surface film formed is composed of a large number of irregular particles with observed crack.Meanwhile

the surface film formed in air shows loose structure with cauliflower-like appearance

and the crack and deformation are very serious.Ignition-proof mechanism reveals that

under nitrogen atmosphere

a protective film is composed of the mixed structure of CaO

MgO

and Mg3N2、Ca3N2 at the outer surface and CaO and MgO at the inner layer

where Ca element aggregated on the folds

impurities

cracks and the junction of surface and substrate.The dense structure compensate the loose hole

which is beneficial for preventing the Mg-5Ca alloy from burning.However

the film under high-purity nitrogen is only composed of Mg3N2 and Ca3N2

and it is very thin

so that it can not cover the surface entirely

resulting in the low ignition-proof efficiency.Film formed in air is composed of mixed structure of CaO and MgO with mostly CaO at the free surface

and it is too thick to bear the pressure

so that the film is broken and the surface quality is the worst.