Dealloying corrosion of anodic and nanometric Mg41Nd5 in solid solution-treated Mg-3Nd-1Li-0.2Zn alloy

The microstructure and chemical compositions of the solid solution-treated Mg-3 Nd-1 Li-0.2 Zn alloy were characterized using optical microscope,scanning electron microscope(SEM),transmission electron microscope(TEM),electron probe micro-analyzer(EPMA)and X-ray photoelectron spectroscopy(XPS).The corrosion behaviour of the alloy was investigated via electrochemical polarization,electrochemical impedance spectroscopy(EIS),hydrogen evolution test and scanning Kelvin probe(SKP).The results showed that the microstructure of the as-extruded Mg-3 Nd-1 Li-0.2 Zn alloy containedα-Mg matrix and nanometric second phase Mg_(41)Nd_(5).The grain size of the alloy increased significantly with the increase in the heat-treatment duration,whereas the volume fraction of the second phase decreased after the solid solution treatment.The surface film was composed of oxides(Nd_(2)O_(3),Mg O,Li_(2)O and Zn O)and carbonates(Mg CO3 and Li_(2)CO3),in addition to Nd.The as-extruded alloy exhibited the best corrosion resistance after an initial soaking of 10 min,whereas the alloy with 4 h-solution-treatment possessed the lowest corrosion rate after a longer immersion(1 h).This can be attributed to the formation of Nd-containing oxide film on the alloys and a dense corrosion product layer.The dealloying corrosion of the second phase was related to the anodic Mg_(41)Nd_(5)with a more negative Volta potential relative toα-Mg phase.The preferential corrosion of Mg_(41)Nd_(5)is proven by in-situ observation and SEM.The solid solution treatment of Mg-3 Nd-1 Li-0.2 Zn alloy led to a shift in corrosion type from pitting corrosion to uniform corrosion under long-term exposure.

Corrosion Resistance of Superhydrophobic Mg(OH)_(2)/Calcium Myristate Composite Coating on Magnesium Alloy AZ31

Hydrophobic Mg(OH)_(2)/calcium myristate(Ca[CH3(CH2)12COO]_(2),CaMS)and Mg(OH)_(2)/magnesium myristate(Mg[CH3(CH2)12COO]2,MgMS)composite coatings were prepared on the alkali-treated AZ31 substrates via both electrodeposition and dipping methods.The morphologies,compositions,and constitutes of the coatings were investigated by using field-emission scanning electron microscopy(SEM),X-ray photoelectron spectroscopy(XPS),and Fourier transform infrared spectrometry(FTIR)together with X-ray diffractometer(XRD).Furthermore,electrochemical(polarization and impedance spectroscopy)and hydrogen evolution tests were applied to evaluate the corrosion resistance.The wettability and adhesive strength of the composite coatings were characterized through water static contact angle(CA),sliding angle(SA),and nano-scratch tests.Results indicated that the better super-hydrophobicity,corrosion resistance,and adhesion were achieved via an electrodeposited process.The corrosion current density(icorr)and hydrogen evolution rate(HER)of the electrodeposited coating were three and one orders of magnitude smaller than the substrate,implying a significantly improved corrosion resistance.This scenario was ascribed to the super-hydrophobicity of electrodeposited composite coating with a contact angle(CA)and slide angle(SA)of 159.2°±0.8°and 5.2°±0.8°,respectively.However,the dipped composite coating was adverse to the improvement of corrosion resistance and adhesion due to the dissolution of the underlying Mg(OH)_(2)layer and smooth surface with less organic fatty acid salt(MgMS)