Microstructures and properties in surface layers of Mg-6Zn-1Ca magnesium alloy laser-clad with Al-Si powders
(1. School of Materials Engineering, Shanghai University of Engineering Science, Shanghai 201620, China;
2. National Engineering Research Center of Light Alloys Net Forming, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China)
Abstract: Laser surface cladding with Al-Si powders was applied to a Mg-6Zn-1Ca magnesium alloy to improve its surface properties. The microstructure, phase components and chemical compositions of the laser-clad layer were analyzed by using X-ray diffractometry (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). The results show that the clad layer mainly consists of α-Mg, Mg2Si dendrites, Mg17Al12 and Al3Mg2 phases. Owing to the formation of Mg2Si, Mg17Al12 and Al3Mg2 intermetallic compounds in the melted region and grain refinement, the microhardness of the clad layer (HV0.025 310) is about 5 times higher than that of the substrate (HV0.025 54). Besides, corrosion tests in the NaCl (3.5%, mass fraction) water solution show that the corrosion potential is increased from -1574.6 mV for the untreated sample to -128.7 mV for the laser-clad sample, while the corrosion current density is reduced from 170.1 to 6.7 μA/cm2. These results reveal that improved corrosion resistance and increased hardness of the Mg-6Zn-1Ca alloy can be both achieved after laser cladding with Al-Si powders.
Key words: laser cladding; Mg-6Zn-1Ca alloy; microstructure; hardness; corrosion resistance