Research On Corrosion Resistance Film Deposited On AZ31magnesium Alloy By The Glow-discharge Plasma Technique

Magnesium is the lightest metal used in engineering. Magnesium alloys have advantageous properties including high specific strength, high specific toughness, low elastic module, excellent damping characteristics, good machinability and dimensional stability, electromagnetic shielding, abundant in resource as well as easy to be recycled. So magnesium alloys have found a wide applications in such area as automobile, computer, electronics, aeronautics and astronautics, sporting goods, handhold tools and household equipment, et al., and been regarded as"green engineering material"with greet potential development in 21st century. However, magnesium and its alloys have several drawbacks including poor resistance to corrosion and wear, poor creep resistance and high chemical reactivity, which restrict their extensive application in many industry fields.In this dissertation, Al-Mg, Al-Cr-Fe, Ni-Cr-Mo-Cu film is prepared by double glow plasmas technique, and there microstructure and corrosion behavior are investigated. The film consists of two different regions, i.e., an amorphous layer on outmost surface and an underlying lamellar nanocrystalline layer with a grain size of less than 10 nm. The corrosion behavior of amorphous/nanocrystalline film in 3.5% NaCl solution is investigated using an electrochemical polarization measurement. Compared with the AZ31 magnesium alloy, the amorphous/nanocrystalline film exhibits more positive corrosion potentials and lower corrosion current densities than that of AZ31 magnesium alloy.In present study, we have found that the novel technique—glow discharge used for making amorphous and nanocrystal film, which break through empirical rules for the achievement of large glass-forming. In the double cathode mode, both target cathode and substrate cathodes are subject to Ar ion sputter by glow discharge. As a result, a large number of nano particles escapes from the surface of one cathode materials and deposit on the surface of the other cathode materials surface. In the mono-cathode mode, due to a stronger ion sputter effect at a higher electrode voltage, the crystalline order on the surface of the electrode was destroyed by the Ar ion attack, leading to atomic displacement and the transformation from a crystalline state to an amorphous state. Meanwhile, a large amount of nanosize amorphous particles by glow discharge sputtering are redeposited on the workpiece surface. Likely, the two mechanisms can be proposed to explain the unique structure of the film formed on the pure iron by mono-cathode glow discharge.