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Laser Surface Melting of AZ31B Magnesium Alloy Under Extreme Cooling Conditions Cooling Conditions
Y.Q. Ge, W.X. Wang, S. Guo, Z.Q. Cui and B.S. Xu

Based on the extreme cooling condition in liquid nitrogen (ECLN) and deep cryogenic treatment (DCT) technique, microstructure and propertiesof the melted layer of AZ31B magnesium alloy with a 5 kW continuous wave (CW) CO2 laser were investigated in the present study by means of optical microscopy (OM), a scanning electron microscope (SEM), microhardness tester and electrochemical corrosion tester. The results showed that the grain size of the surface was obviously refined, and the grain size obtained by DCT was much smaller than that by ECLN. The phases of α-Mg and β-Mg17Al12 were precipitated in the melted zone with a peculiar distribution and content. The maximum microhardness of the melted layer was 140% of the substrate. Both ECLN and DCT led to the decline of corrosion resistance, but the corrosion potential of the DCT layer (-1.453 eV) was higher than that of the ECLN layer (-1.487 V), indicating that DCT could improve the decline of the magnesium corrosion resistance to a certain degree.

Keywords: CO2 laser, AZ31B magnesium alloy, laser melting, liquid nitrogen cooling, deep cryogenic treatment

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