Aluminum films with thickness of 8.78-20.82 μm were deposited on the AZ31B magnesium alloys by DC magnetron sputtering. The influences of aluminum film on the micro-mechanical properties and corrosion behavior of the magnesium alloys were investigated. The morphology of aluminum film was examined by scanning electron microscopy and the microstructure of aluminum film was analyzed by X-ray diffractometry. Nanoindentation and nanoscratch tests were conducted to investigate their micro- mechanical properties. Moreover, potentiodynamical polarization test performed in 3.5%NaCl solution was carried out to study their anticorrosion performances. The results show that the surface hardness of AZ31B magnesium alloy with aluminum film is 1.38-2.01 GPa, higher than that of the magnesium alloy substrate. The critical load of Al film/AZ31B substrate is in the range of 0.68-2.77 N. The corrosion current density of AZ31B with aluminum film is 2-3 orders of magnitude less than that of bare AZ31B. And the corrosion potential with aluminum film positively shifts. Thus aluminum film can increase the corrosion resistance of Mg alloys obviously.

Aluminum films with thickness of 8.78−20.82 μm were deposited on the AZ31B magnesium alloys by DC magnetron sputtering. The influences of aluminum film on the micro-mechanical properties and corrosion behavior of the magnesium alloys were investigated. The morphology of aluminum film was examined by scanning electron microscopy and the microstructure of aluminum film was analyzed by X-ray diffractometry. Nanoindentation and nanoscratch tests were conducted to investigate their micro- mechanical properties. Moreover, potentiodynamical polarization test performed in 3.5%NaCl solution was carried out to study their anticorrosion performances. The results show that the surface hardness of AZ31B magnesium alloy with aluminum film is 1.38−2.01 GPa, higher than that of the magnesium alloy substrate. The critical load of Al film/AZ31B substrate is in the range of 0.68−2.77 N. The corrosion current density of AZ31B with aluminum film is 2−3 orders of magnitude less than that of bare AZ31B. And the corrosion potential with aluminum film positively shifts. Thus aluminum film can increase the corrosion resistance of Mg alloys obviously.

Anodization of rare earth-containing Mg alloy of Mg-3Nd-0.2Zn-0.4Zr (mass fraction, %) (NZ30K) was performed in composite electrolyte containing NaOH, KOH, K2SiO3, Na2SiO3, NaF, KF etc. The anodic coating was characterized by using X-ray diffraction(XRD), field emission electron scanning microscope(FE-SEM) and electron probe microscopic analysis(EPMA). The corrosion resistance of the anodized alloy and the substrate was evaluated in 5% NaCl solution using electrochemical impedance spectroscopy(EIS). The results of XRD show that the anodic coating is mainly composed of MgO. EPMA indicates that magnesium and oxygen are almost uniformly distributed across the coating, and the fluorine content decreases gradually from the interface of coating-substrate to the surface, whereas the distribution of silicon is reverse to that of fluorine. The results of EIS analysis shows that the anodic coating exhibits the superior corrosion resistance for NZ30K alloy.

Anodization of rare earth-containing Mg alloy of Mg-3Nd-0.2Zn-0.4Zr (mass fraction, %) (NZ30K) was performed in composite electrolyte containing NaOH, KOH, K₂SiO₃, Na₂SiO₃, NaF, KF etc. The anodic coating was characterized by using X-ray diffraction(XRD), field emission electron scanning microscope(FE-SEM) and electron probe microscopic analysis(EPMA). The corrosion resistance of the anodized alloy and the substrate was evaluated in 5% NaCl solution using electrochemical impedance spectroscopy(EIS). The results of XRD show that the anodic coating is mainly composed of MgO. EPMA indicates that magnesium and oxygen are almost uniformly distributed across the coating, and the fluorine content decreases gradually from the interface of coating-substrate to the surface, whereas the distribution of silicon is reverse to that of fluorine. The results of EIS analysis shows that the anodic coating exhibits the superior corrosion resistance for NZ30K alloy.

The electroless Ni-P/Ni-W-P duplex coatings were deposited directly on AZ91D magnesium alloy by an acid-sulfate nickel bath. Nickel sulphate and sodium tungstate were used as metal ion sources and sodium hypophosphite was used as reducing agent. The coating was characterized for its structure, morphologies, microhardness and corrosion properties. The presence of dense and coarse nodules in the duplex coatings was observed by SEM and EDS. Tungsten content in Ni-P/Ni-W-P alloy is about 0.65%(mass fraction) and the phosphorus content is 8.18%(mass fraction). The microhardness of the coatings is 622 VHN. The coating shows good adhesion to the substrate. The results of electrochemical analysis, the porosity and the immersion test show that Ni-P/Ni-W-P duplex coatings possess noble anticorrosion properties to protect the AZ91D magnesium alloy.

The electroless Ni-P/Ni-W-P duplex coatings were deposited directly on AZ91D magnesium alloy by an acid-sulfate nickel bath. Nickel sulphate and sodium tungstate were used as metal ion sources and sodium hypophosphite was used as reducing agent. The coating was characterized for its structure, morphologies, microhardness and corrosion properties. The presence of dense and coarse nodules in the duplex coatings was observed by SEM and EDS. Tungsten content in Ni-P/Ni-W-P alloy is about 0.65%(mass fraction) and the phosphorus content is 8.18%(mass fraction). The microhardness of the coatings is 622 VHN. The coating shows good adhesion to the substrate. The results of electrochemical analysis, the porosity and the immersion test show that Ni-P/Ni-W-P duplex coatings possess noble anticorrosion properties to protect the AZ91D magnesium alloy.

Chromium-plating is considered an effective method to improve surface properties of metal materials. Magnetron sputtering was applied to prepare Cr coating on AZ31 magnesium alloy and the influence of bias voltage on properties of Cr coating was investigated. The obtained coatings present an (110) preferred texture and have a developed columnar structure. With increasing bias voltage, the surface structure of Cr coating becomes denser. All of the Cr-coated AZ31 have much higher surface microhardness than bare AZ31. The Cr coating deposited on AZ31 at bias voltage of −150 V has a higher corrosion potential than others. The result of the immersion test shows that it decreases the damaged area compared with bare AZ31. The failure of the coated AZ31 is mainly attributed to the existence of through-thickness defects in the coating.

Chromium-plating is considered an effective method to improve surface properties of metal materials. Magnetron sputtering was applied to prepare Cr coating on AZ31 magnesium alloy and the influence of bias voltage on properties of Cr coating was investigated. The obtained coatings present an (110) preferred texture and have a developed columnar structure. With increasing bias voltage, the surface structure of Cr coating becomes denser. All of the Cr-coated AZ31 have much higher surface microhardness than bare AZ31. The Cr coating deposited on AZ31 at bias voltage of -150 V has a higher corrosion potential than others. The result of the immersion test shows that it decreases the damaged area compared with bare AZ31. The failure of the coated AZ31 is mainly attributed to the existence of through-thickness defects in the coating.

Corrosion behavior of AZ91 magnesium alloy in simulating acid rain under wet-dry cyclic condition was investigated. The results show that corrosion potential shifts positively and the corrosion current density decreases at low wet-dry cyclic time. Further increase of the cyclic time results in the negative movement of corrosion potential and the increase of current density. SEM observation indicates that corrosion occurs only in α phase, β phase is inert in corrosive medium, and the corrosion of AZ91 magnesium appears in uniform characteristic. XPS analysis suggests that the corrosion product is mainly composed of oxide and hydroxide of magnesium and aluminum, and a small amount of sulfate is also contained in the film.

Corrosion behavior of AZ91 magnesium alloy in simulating acid rain under wet-dry cyclic condition was investigated. The results show that corrosion potential shifts positively and the corrosion current density decreases at low wet-dry cyclic time. Further increase of the cyclic time results in the negative movement of corrosion potential and the increase of current density. SEM observation indicates that corrosion occurs only in α phase, β phase is inert in corrosive medium, and the corrosion of AZ91 magnesium appears in uniform characteristic. XPS analysis suggests that the corrosion product is mainly composed of oxide and hydroxide of magnesium and aluminum, and a small amount of sulfate is also contained in the film.

Magnesium alloys covered with metal coating display excellent corrosion resistance, wear resistance, conductivity and electromagnetic shielding properties. The electroless plating Ni-P as bottom layer following the electroplating nickel as surface layer on AZ91D magnesium alloy was investigated. The coating surface morphology was observed with SEM and the structure was analyzed with XRD. Electrochemical tests and salt spray tests were carried out to study the corrosion resistance. The experimental results indicate that the dual coating is uniform, compact and pore-free. The adhesion strength between magnesium alloy substrate and electroless plating Ni-P bottom layer and electroplating nickel surface layer is perfect. The corrosion resistance of AZ91D magnesium alloy is greatly improved after being protected with the dual coating.

Magnesium alloys covered with metal coating display excellent corrosion resistance, wear resistance, conductivity and electromagnetic shielding properties. The electroless plating Ni-P as bottom layer following the electroplating nickel as surface layer on AZ91D magnesium alloy was investigated. The coating surface morphology was observed with SEM and the structure was analyzed with XRD. Electrochemical tests and salt spray tests were carried out to study the corrosion resistance. The experimental results indicate that the dual coating is uniform, compact and pore-free. The adhesion strength between magnesium alloy substrate and electroless plating Ni-P bottom layer and electroplating nickel surface layer is perfect. The corrosion resistance of AZ91D magnesium alloy is greatly improved after being protected with the dual coating.

Poor corrosion resistance limits the application of magnesium alloys. Conversion coating is widely used to protect magnesium alloys because of easy operation and low cost. A novel conversion coating on die-cast AZ91D magnesium alloy containing barium salts was studied. The optimum concentrations of Ba(NO₃)₂, Mn(NO₃)₂ and NH₄H₂PO₄ are 25 g/L, 15 mL/L and 20 g/L, respectively, based on orthogonal test results. The treating time, solution temperature and pH value are settled to be 5-30 min, 50-70 ℃ and 2.35-3.0, respectively. The corrosion resistance of barium conversion coating is better than that of manganese-based phosphate conversion coating by immersion test. The coating is composed of Ba, P, O, Mg, Zn, Mn and Al by EDX analysis.

Poor corrosion resistance limits the application of magnesium alloys. Conversion coating is widely used to protect magnesium alloys because of easy operation and low cost. A novel conversion coating on die-cast AZ91D magnesium alloy containing barium salts was studied. The optimum concentrations of Ba(NO3)2, Mn(NO3)2 and NH4H2PO4 are 25 g/L, 15 mL/L and 20 g/L, respectively, based on orthogonal test results. The treating time, solution temperature and pH value are settled to be 5−30 min, 50−70 ℃ and 2.35−3.0, respectively. The corrosion resistance of barium conversion coating is better than that of manganese-based phosphate conversion coating by immersion test. The coating is composed of Ba, P, O, Mg, Zn, Mn and Al by EDX analysis.

Golden yellow rare earths chemical conversion coating was obtained on the surface of magnesium alloy by immersing in cerium sulfate solution. The corrosion resistance of RE conversion coating was evaluated using immersion test and potentiodynamic polarization measurements in 3.5% NaCl solution. The morphologies of samples before corrosion and after corrosion were observed by SEM. The structures and compositions of the RE conversion coating were studied by means of XPS, XRD and IR. The results show that, the conversion coating consists of mainly two kinds of element Ce and O, the valences of cerium are +3 and +4, and OH− exists in the coating. The anti-corrosion property of magnesium alloy is increased obviously by rare earths conversion coating, Its self-corrosion current density decreases and the coating has self-repairing capability in the corrosion process in 3.5% NaCl solution.

Golden yellow rare earths chemical conversion coating was obtained on the surface of magnesium alloy by immersing in cerium sulfate solution. The corrosion resistance of RE conversion coating was evaluated using immersion test and potentiodynamic polarization measurements in 3.5% NaCl solution. The morphologies of samples before corrosion and after corrosion were observed by SEM. The structures and compositions of the RE conversion coating were studied by means of XPS, XRD and IR. The results show that, the conversion coating consists of mainly two kinds of element Ce and O, the valences of cerium are +3 and +4, and OH- exists in the coating. The anti-corrosion property of magnesium alloy is increased obviously by rare earths conversion coating, Its self-corrosion current density decreases and the coating has self-repairing capability in the corrosion process in 3.5% NaCl solution.

The effects of increase extent of voltage on the wear resistance and corrosion resistance of micro-arc oxidation (MAO) coatings on AZ91D magnesium alloy were investigated in silicate electrolyte. The results show that with increasing extent of voltage, both of the thickness and bonding force of MAO coatings first increase, and then decrease. These parameters are all up to their maximum values when the increase extent of voltage is 20 V. The roughness of the coatings always increases. The coating has the best corrosion resistance when the increase extent of voltage is not below 25 V, and the coating has the best wear resistance when the increase extent of voltage is 10 V. The wear mechanisms for the micro-arc oxidation are abrasive wear and micromachining wear. These are related to their microstructures.

The effects of increase extent of voltage on the wear resistance and corrosion resistance of micro-arc oxidation (MAO) coatings on AZ91D magnesium alloy were investigated in silicate electrolyte. The results show that with increasing extent of voltage, both of the thickness and bonding force of MAO coatings first increase, and then decrease. These parameters are all up to their maximum values when the increase extent of voltage is 20 V. The roughness of the coatings always increases. The coating has the best corrosion resistance when the increase extent of voltage is not below 25 V, and the coating has the best wear resistance when the increase extent of voltage is 10 V. The wear mechanisms for the micro-arc oxidation are abrasive wear and micromachining wear. These are related to their microstructures.

The mechanical characteristics of the macro-arc oxidation (MAO) coating on Mg alloy AZ91 were examined by means of nano scratch tester. The corrosion and erosion corrosion behavior of AZ91 with and without MAO coating were investigated by using potentiodynamic electrochemical technique and micro-abrasion tribometer in simulated body fluids, respectively. The influence of HCO3− ions on the erosion corrosion was discussed. The results show that the coating and its substrate are in a pronounced bond. The MAO coating increases 1−2 orders of magnitude of the corrosion resistance of AZ91 alloy. HCO3− ions enhance the corrosion rates of the AZ91 alloys more significantly than the alloys with MAO coating. However, there exists an obvious passivation process of AZ91 without coating in the HCO3− solutions. Moreover, an MgCO3 film formed in HCO3− containing solutions leads to an enhancement in micro-wear resistance. MAO coating deteriorates the erosion corrosion resistance of AZ91 alloy due to the formation of oxidation debris resulted from the broken MAO coating.

The mechanical characteristics of the macro-arc oxidation (MAO) coating on Mg alloy AZ91 were examined by means of nano scratch tester. The corrosion and erosion corrosion behavior of AZ91 with and without MAO coating were investigated by using potentiodynamic electrochemical technique and micro-abrasion tribometer in simulated body fluids, respectively. The influence of HCO₃^- ions on the erosion corrosion was discussed. The results show that the coating and its substrate are in a pronounced bond. The MAO coating increases 1-2 orders of magnitude of the corrosion resistance of AZ91 alloy. HCO₃^- ions enhance the corrosion rates of the AZ91 alloys more significantly than the alloys with MAO coating. However, there exists an obvious passivation process of AZ91 without coating in the HCO₃^- solutions. Moreover, an MgCO₃ film formed in HCO₃^- containing solutions leads to an enhancement in micro-wear resistance. MAO coating deteriorates the erosion corrosion resistance of AZ91 alloy due to the formation of oxidation debris resulted from the broken MAO coating.

A technology for preparation of a cathodic phosphate coating mainly containing nano metallic zinc particles and phosphate compounds on magnesium alloy was developed. The influence of cathodic current density on the microstructure of the cathodic phosphate coating was investigated. The results show that the crystals of the coating are finer and the microstructures of the outer surface of the coatings are zigzag at the cathodic density of 0.2-0.5 A/dm².The content of nano metallic zinc particles in the coating decreases with the increase of the thickness of the coatings and tends to be zero when the coating thickness is 4.14 mm. The cathodic phosphate coating was applied to be a transition coating for improving the adhesion between the paints and the magnesium alloys. The formation mechanism of the cathodic phosphate coating was investigated as well.

A technology for preparation of a cathodic phosphate coating mainly containing nano metallic zinc particles and phosphate compounds on magnesium alloy was developed. The influence of cathodic current density on the microstructure of the cathodic phosphate coating was investigated. The results show that the crystals of the coating are finer and the microstructures of the outer surface of the coatings are zigzag at the cathodic density of 0.2−0.5 A/dm2. The content of nano metallic zinc particles in the coating decreases with the increase of the thickness of the coatings and tends to be zero when the coating thickness is 4.14 m. The cathodic phosphate coating was applied to be a transition coating for improving the adhesion between the paints and the magnesium alloys. The formation mechanism of the cathodic phosphate coating was investigated as well.

The magnetic force acting on workpiece to be machined plays a significantly important role in magnetic abrasive polishing process. But in a case of polishing nonferrous materials, the strength of magnetic force is very low and it leads lower polishing efficiency. The magnesium alloy that has superior mechanical properties for industrial application such as a lightweight and high specific strength is one of the most famous nonferrous materials. An improving strategy of the magnetic force for the AZ31 magnesium alloy installed with a permanent magnet was proposed and experimental verification was carried out. For the proposed strategy, the effect of process parameters on the surface roughness of the AZ31 magnesium alloy was evaluated by a design of experimental method.

The magnetic force acting on workpiece to be machined plays a significantly important role in magnetic abrasive polishing process. But in a case of polishing nonferrous materials, the strength of magnetic force is very low and it leads lower polishing efficiency. The magnesium alloy that has superior mechanical properties for industrial application such as a lightweight and high specific strength is one of the most famous nonferrous materials. An improving strategy of the magnetic force for the AZ31 magnesium alloy installed with a permanent magnet was proposed and experimental verification was carried out. For the proposed strategy, the effect of process parameters on the surface roughness of the AZ31 magnesium alloy was evaluated by a design of experimental method.

Polymeric nano-film on the surface of Mg-Mn-Ce magnesium alloy was fabricated by polymer plating of 6-dihexylamino-1, 3, 5-triazine-2, 4-dithiol monosodium (DHN) to improve its corrosion resistance. The electrochemical reaction process was analyzed by cyclic voltammetry and two obvious peaks of oxidation reaction were observed. The static contact angle of distilled water on polymer-plated surface can be up to 106.3° while on the blank surface it is 45.8°. Potentiodynamic polarization results show that the polymeric film can increase the corrosion potential from -1.594 V vs SCE for blank to -0.382 V vs SCE. The results of electrochemical impedance spectroscopy indicate that the charge transfer resistances of blank and polymer-plated Mg-Mn-Ce alloy are 485 Ω.cm² and 2 717 Ω.cm², respectively. The method of polymer plating can provide a novel approach for fabricating hydrophobic film on Mg-Mn-Ce alloy surface and improving its anti-corrosion property.

Polymeric nano-film on the surface of Mg-Mn-Ce magnesium alloy was fabricated by polymer plating of 6-dihexylamino-1, 3, 5-triazine-2, 4-dithiol monosodium (DHN) to improve its corrosion resistance. The electrochemical reaction process was analyzed by cyclic voltammetry and two obvious peaks of oxidation reaction were observed. The static contact angle of distilled water on polymer-plated surface can be up to 106.3˚ while on the blank surface it is 45.8˚. Potentiodynamic polarization results show that the polymeric film can increase the corrosion potential from −1.594 V vs SCE for blank to −0.382 V vs SCE. The results of electrochemical impedance spectroscopy indicate that the charge transfer resistances of blank and polymer-plated Mg-Mn-Ce alloy are 485 Ω∙cm2 and 2 717 Ω∙cm2, respectively. The method of polymer plating can provide a novel approach for fabricating hydrophobic film on Mg-Mn-Ce alloy surface and improving its anti-corrosion property.

A novel anodization which is environmentally friendly, low voltage and low energy consumption was developed to improve corrosion resistance of AZ31 magnesium alloy. The corrosion resistance of the anodic films was studied by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques. The microstructure and compositions of films were examined by SEM, XPS and XRD. A new kind of organic additive used in the electrolyte is friendly to the environment. The compact, intact and uniform coating with high hardness can be prepared on AZ31 magnesium alloy by the environmentally friendly anodization, which enhances the corrosion resistance of AZ31 Mg alloy significantly.

A novel anodization which is environmentally friendly, low voltage and low energy consumption was developed to improve corrosion resistance of AZ31 magnesium alloy. The corrosion resistance of the anodic films was studied by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques. The microstructure and compositions of films were examined by SEM, XPS and XRD. A new kind of organic additive used in the electrolyte is friendly to the environment. The compact, intact and uniform coating with high hardness can be prepared on AZ31 magnesium alloy by the environmentally friendly anodization, which enhances the corrosion resistance of AZ31 Mg alloy significantly.