Laser processing of Mg-10Li-3Al-3Zn alloy：Part II- Improving corrosion resistance of multi-phase Mg alloys by laser surface processing

In Part Ⅰ of this series, it can be found that the corrosion resistance of metals in the welded seam zone (WSZ) was far higher than that of the base metal (BM) of MBLS10A-200 Mg-Li alloy. Therefore, the feasibility of improving the corrosion resistance of MBLS10A-200 Mg-Li alloy through laser surface melting (LSM) was further explored. Meanwhile, laser shock peening (LSP) treatment was also used for contrast. The results showed that the surface melted zone with the corrosion resistance through LSM superior to that of metals in WSZ of MBLS10A-200 alloy through laser welding can be prepared by controlling heat input through increasing the scanning speed of laser beam, while LSP has limited impact on the electrochemical corrosion resistance of MBLS10A-200 alloy. The corrosion current density (J_corr) of the samples subjected LSM declined by two orders of magnitude compared with the base metal (BM) while the charge transfer resistance increased by 17 times compared with BM. An analysis indicated that owing to the fast cooling rate during laser processing, the multi-phase microstructures (i.e. α phase, β phase and Li₂MgAl) of BM were transformed into β single-phase microstructure in WSZ and surface melted zone. In this way, not only solid solution strengthening of the metals in WSZ was realized but also the micro-galvanic coupling generated due to the difference of electric potentials of multi-phase microstructures were reduced, thus improving the corrosion resistance of surface melted zone.