Magnesium (Mg) alloys are the lightest engineering structure materials widely used in aerospace, transportation and electronic communications, etc. The poor wear resistance and corrosion resistance of Mg alloys restrict directly its wide application. Therefore, it is of great significance to improve the wear resistance and corrosion resistance of Mg alloy. Surface treatment is one of the effective methods to improve the wear resistance and corrosion resistance of Mg alloys. Thereinto, surface nanocrystallization has great potential for development and application due to its two advantages: (1) the microstructures present a gradient change along the thickness direction, no peeling and separation are occurred, no interfaces are considered; (2) traditional surface mechanical treatment or simple improvement can be achieved. At present, surface nanocrystallization of Mg alloys used commonly includes surface mechanical attrition treatment (SMAT), laser shot peening (LSP), ultrasonic shot peening (UST), high energy shot peening (HESP), supersonic particle bombardment, etc. The basic principles of SMAT, HESP, UST are similar, the only difference is the vibration frequency. According to the vibration frequency from big to small, that is, UST, HESP, SMAT. Mg alloys with different composition after surface treatment obtain nanometer grain size as low as 20 nm. In addition, surface mechanical rolling technology (SMRT) is developed by refitting the SMA equipment. The thickness of nanolayer reaches 100 μm by SMRT. For LSP technology, the thickness of nanolayer is about 20 μm, the nanometer grain size reaches 20 nm. Furthermore, LSP has a better advantage in corrosion resistance due to the low surface roughness. The nanoscale grain of Mg alloys can reach up to 10 nm by supersonic particle bombardment technology. Meanwhile, the thickness of nanolayer is higher than that of LSP. No matter what surface nanocrystallization technology is used, the surface structure layer of Mg alloys can be divided into four layers from the surface to interior: surface nanocrystallization layer, surface fine grain layer, coarse-grained strain layer and α-Mg matrix. The strain energy is the main factor affecting the nanograin size and nanolayer. Meanwhile, the microhardness of Mg alloys increases obviously after surface nanocrystallization, which can improve the friction and wear properties. The corrosion resistance of Mg alloys is mainly affected by the grain size and the particle size and volume fraction of second phases. The corrosion resistance increases with the grain size refinement in a certain grain size range. Except for the effect of surface roughness of Mg alloys, the corrosion mechanism is not clear in Mg alloys after surface nanocrystallization. In particular, the effect of the nanograin size and the particle size and volume fraction of second phases on the corrosion mechanism of Mg alloys should be further improved and optimized. This paper reviewed the preparation process and characteristics of the surface nanocrystallization technology (surface mechanical attrition treatment, ultrasonic peening treatment, high-energy shot peening, laser shock processing and high velocity oxygen fuel) of Mg alloys. It mainly introduced the research status of the surface nanocrystallization of Mg alloys. Meanwhile, the influence of surface nanocrystallization on the Microstructure, mechanical properties and corrosion behavior of Mg alloys is analyzed. And the application prospect and existing problems to be solved are discussed. © 2019, Materials Review Magazine. All right reserved.
