| Magnesium alloys are widely used in aerospace,automotive,electronics and other fields due to their light weight and high specific strength.Since the discovery of quasicrystals in the Mg-Zn-RE series in the 1990 s,Mg-Zn-Y-Zr alloys have more excellent properties than Mg-Al alloys(such as high strength,creep resistance,thermal stability properties,plasticity and corrosion resistance)and has become one of the hot research materials in the field of rapid solidification.The alloy also has the disadvantages of the conventional grade Mg alloy.Compared with other materials,its corrosion resistance and friction and wear performance are still low and severely restrict its development.Considering that the laser surface treatment operation in the field of surface modification of metal materials has advantages such as simplicity,no pollution,and selective modification of the local surface of parts.Therefore,it was decided to use laser remelting and laser cladding technology to specifically enhance the hardness,corrosion resistance and friction and wear resistance of the rare earth magnesium alloy.Correspondingly,the application potential of rare earth magnesium alloys has been expanded and developed,which has profound practical significance.The laser remelting experiment of Mg-1.85Y-7.91Zn-0.75Zr(wt%)alloy at different powers and the laser cladding experiment at the same laser power were performed by using a 3kW DILAS semiconductor laser.The microstructure,morphology,phase composition and distribution of the prepared samples were observed with an optical microscope(OM),an electron scanning microscope(SEM),an X-ray diffractometer(XRD)and an energy spectrometer(EDS);The Vickers hardness was measured by a micro-hardness tester;the friction and wear performance of the sample was tested by a friction and abrasion tester;the elastic modulus and hardness of the sample were tested by a nano-indentation machine;Corrosion resistance was tested by an electrochemical tester.The results show that the macro-solidified structure of the remelted alloy is significantly refined,and with the increase of power,the grains become larger and the second phase distribution becomes more dispersed.Due to the effects of fine grain strengthening,solid solution strengthening,and dispersion strengthening,hardness,wear resistance,elastic modulus and corrosion resistance are improved.For the laser cladding sample,the average hardness of the cladding sample with 10% nm SiC is the highest due to the formation of the hardened phase.Its value is 4.06 times that of the substrate.Compared with the four laser cladding samples,the cladding sample with 5% nm SiC has the smallest coefficient of friction and the highest wear resistance.The polarization curve measured in NaCl(3.5 wt%)aqueous solution shows that the corrosion resistance is most significantly improved for samples coated with 10% nm SiC.The results show that both laser remelting and laser cladding are effective methods to improve the surface properties of magnesium rare earth alloys,and laser cladding of nano-sized SiC is one of the most significant improvements.It can be considered that this method will be widely used in future production practices for protection against wear and corrosion. |
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