The surface properties of magnesium alloys can be improved by Laser Cladding in order to increase wear and corrosion resistance manteining the lower density of these alloys. This can make magnesium alloys a promising structural material to be used as a substitute for metals traditionally used in the automotive and aircraft sector.
2. Laser Alloying, Glazing, and Cladding
Laser cladding is a coating manufacture method with which it is possible to obtain low porous and improved properties coatings on different materials (mainly metals) using a laser as energy source. Based on the feed material, the amount of molten substrate and the laser parameters, three varieties of this process can be established: laser alloying, laser glazing and laser cladding. In the three cases, the high cooling rate and, consequently the quick solidification during the fabrication process is the main advantage of these methods, because it results in a fine microstructure and improved mechanical properties. During the solidification process, the melted metal liquid atoms are joined together at the nucleation points and start to form crystals. These crystals grow and form grains in the direction of the solidification, however, due to the high cooling rates, these grains have no time to become bigger, and their size ends up being very small in this kind of process. Small grain sizes result in high number of grain limits and, consequently, in high hardness and mechanical properties 
Laser alloying technique allows to melt simultaneously the feeding material and the substrate obtaining a homogeneous alloyed metal. In general, the coating is not very thick because the amount of spraying material is low 
Laser glazing allows to melt only a small part of the substrate and cool it very quickly (1010
K/s), which forms amorphous crystal 
Coatings with different composition to the substrate have been successfully fabricated by Laser cladding technique since this method produces a minimum dilution of the substrate allowing the coating to maintain the feed material properties. Moreover, a fine coating microstructure is obtained due to the quick cool rate. To achieve this, the control of the laser parameters is very important.
The main problem of lasers techniques on magnesium alloys is that the use of magnesium as a substrate, together with high values of laser power, can produce a dilution of the magnesium from the substrate to within the coating matrix due to the low melting points of magnesium alloys (~560 °C) that makes them liable to be melted during the laser cladding process. Nevertheless, this dilution changes with the processing parameters, therefore, obtaining a minimal dilution rate is possible. Indeed, the three methods of coatings fabrication (laser alloying, laser glazing and laser cladding) are feasible on magnesium alloys.
For instance, Ignat et al. 
obtained hardened high corrosion resistance Al/Mg coatings on WE43 and ZE41 magnesium alloys by laser alloying. Other authors such as Yue, Su, and Yang 
and Huang et al. 
developed amorphous coatings by laser glazing. However, avoiding dilution is possible by using low laser power. Yang et al. 
used laser cladding to coat ZE91D magnesium alloys with Al + (Ti + B4
C) composite coatings and A. H. Wang et al. 
utilized laser cladding to repair surface areas of magnesium components.
Obtaining improved coatings with homogeneous compositions, low porosity, minimal interactions between the molten pool and the sprayed material, and greater properties depends on the laser parameters and on the amount of the feed material used. Indeed, most laser cladding coatings are actually laser alloying coatings.
shows a scheme of laser alloying, glazing and cladding. The classification is based on the mixed composition between the magnesium of the substrate and the elements of the coatings 
. In addition, Figure 1
shows an example of the resulting microstructure. The main differences between the microstructure showed in Figure 1
a,c is that in the case of laser alloying, there is a higher dilution between the coating and the substrate, and the resultant material is embedded in the substrate surface. In the case of the laser cladding microstructure, the coating is on the substrate surface, not embedded in the substrate. In the case of the laser glazing microstructure shown in Figure 1
b, the morphology/shape of the coating is similar to laser cladding, however, the coating is an amorphous crystal.