| Mg alloy as one of the lightest metal structural material on earth.There are characteristics of low density,high specific strength and specific stiffness,stable machining dimension,good thermal conductivity and electrical conductivity,easy process and suitable for recycling.These features meeting environmental protection make Mg alloys in electronics,aerospace and automotive apply more and more.However,with the rapid economic development and increasing demand for industrial modernization,many machines need to work in high temperature,high pressure,high speed and even corrosive media,the strength,hardness and corrosion resistance of Mg is far from meeting the requirements in these environments.Considering the environmental protection,two methods of Mg alloy material surface property were used.One was laser surface modification technology,and the other is a HVOF modified technique.Mainly using devices such as metallurgical microscope,scanning electron microscopy,X-ray diffraction and micro-hardness tester,the MFT-400 multifunctional material surface performance tester and CS350 type corrosion electrochemical workstation for coating composition,microstructure,section phase,micro-hardness and wear resistance and corrosion resistant performance of two kinds of progress layer were analyzed and studied.Multipass lap fabrication parameters were determined by single-channel optimization parameters before laser surface modification experiments:frequency of 10 Hz,the scanning speed of 200 mm/min,the amount of defocus 30 mm,current of 80 A,coating thickness of 200 ?m.Coating of laser surface modification technology has the typical characteristics of rapid solidification.Alloyed layer organization is also a hybrid structure composed with planar,col? mnar and dendritic crystal.Fine-grain strengthening and precipitation strengthening are main reasons of razied alloying layer hardness.Coating wear of laser surface treatment than that of the base magnesi ? m alloy were improved.The friction mechanism of the magnesi ?m substrate is mainly adhesion wear,assistant abrasive wear.The precipitation strengthening,fine-grain strengthening,layer enhancement and the transformation of the friction mechanism of alloying coating layer can help improve the coating wear resistance.Rapid condensation in alloying process is a major cause of increasing alloying layer corrosion resistance.But due to the addition of carbon nanotubes and Al powder will react with Mg in NaCl solution,the peeling coating was not conducive to the improvement of the corrosion resistance.The particle fused and impact matrix rapidly in HVOF,its strengthening mechanism are mainly fine-grain strengthen and mechanical reinforcement.Coating spraying typical lamellar structure can be seen from the morphology of high entropy alloy;AlSi12 coating are relatively uniform;there is the emergence of the eutectic silicon.Al coating organization is most dense,and There appears has precipitated phase in coating.High entropy alloy coating composed with a solid solution having a BCC structure and FCC structure,solid solution strengthening,mechanical strengthening and grain refinement makes the coating hardness and wear resistance is greatly improved,the average hardness of high entropy alloy coating of 460 HV,is 8 times of the substrate.In addition,the appearance of eutectic silicon AlSi12 also effectively improve the coating hardness in the coating.The lamellar structure of spraying layer of coatings decide that wear mechanism is mainly adhesive wear.By test results of coating polarization curve of corrosion resistance can be seen,Grain refinement and mechanical reinforcement will help improve the coating corrosion resistance.High entropy alloys coating corrosion resistance improved significantly connected with the joining with corrosion resisting elements such as Ni?Si?Cr. |
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