Microstructures And Properties Of Magnesium Alloy AZ31B After Laser Surface Treatment

In this paper, the melting treatment to AZ31B magnesium alloy is curried withYLS-3000laser on the surface of the sample, and it is investigated that the effect of laserpower and laser scanning speed on the macro-size, microstructure and hardness of the meltedzone. The result shows that the shape of melted zone is crescent after melting treatmentperformed on AZ31B magnesium alloy. The width and depth of the melted zone increasegradually with the increase of the laser power and the decrease of the laser scanning speed.The metallographic analysis indicates that after laser melting treatment the microstructure ofthe melted zone consists of fine dendrite and the granular-Mg17Al12distributing between thedendrites. From the bottom to the surface of the melted zone, the microstructure becomesthinner gradually and the hardness also increases gradually. As the decrease of the laser poweror the increase of the laser scanning speed, the size of the melted zone decreases gradually,the microstructure becomes thinner and the microhardness increases significantly at the sametime. Compared with that before the treatment of laser melting, the microhardness increasessignificantly, owing to the refinement of the microstructure and the formation of theintermetallic compound-Mg17Al12. When the laser power changes from300W to1200Wand the scanning speed changes from0.001m/s to0.09m/s, the increasing extent of thehardness is from24%to84%. The pole figure analysis shows that when the laser surfacemelting treatment, the growth of-Mg dendrite in the melted zone displays obviouslypreferred orientation, and this lead to the significant (0001) basal texture.The laser alloying with Al and Zn powder on AZ31B magnesium alloy surface is curriedwith Presetting methods, and it is investigated that the effect of the laser power and thescanning speed on microstructure and hardness of the alloyed zone. The metallographicanalysis and X-ray diffraction analysis show that the microstructure of the alloyed zone issimilar to the microstructure of the melting treatment, that is, the microstructure consists ofthe fine-Mg dendrite and the intermetallic compound-Mg17Al12distributing between thedendrites, and from the bottom to the surface of the melted zone the microstructure becomesthinner gradually, but the quantity of the granular-Mg17Al12is obviously more than themelting treatment. The microhardness determination shows that the hardening effect of thesurface layer is more obvious than the melting treatment. As the decrease of the laser power orthe increase of the scanning speed, the size of the alloyed zone decreases gradually, themicrostructure is refined gradually, and the microhardness increases gradually. When the laserpower changes from600W to1000W and the scanning speed changes from0.02m/s to0.07m/s, the microhardness improves from72.9%to122%compared with that before thelaser melting treatment. The strengthening effect of the surface layer after laser alloyingtreatment is better than the laser melting treatment, because Al is melted into the alloyed zoneand lead to increasing the quantity of the β-Mg17Al12between dendrites. The pole figure analysis shows that, similar to the melting treatment, when the alloying treatment the growthof-Mg dendrite in the melted zone displays obviously preferred orientation, leading to theobvious (0001) basal texture.