Microstructure And Properties Of Surface Alloying Of Al-Pb And Al-Zr Coating Prepared By Mechanical Alloying And High Current Pulsed Electron Beam

This paper reports the surface morphology and properties of Al substrates with Pb coating and Zr coating,which was deposited by mechanical milling and then treated by high current pulsed electron beam（HCPEB）irradiation respectively.The Al-Pb mixed systems were subjected to mill for different time（1h 2h 3h）at room temperature,then irradiated 10,20 and 30 pulses respectively.The Al-Zr mixed systems were subjected to mill for 1h at room temperature,then irradiated 10,20,30and 40 pulses respectively.The sample surface of microstructure was characterized by using X-ray diffraction（XRD）,transmission electron microscope（TEM）,field emission scanning electron microscope（SEM）and 3D laser scanning microscope（3D LSM）.At the same time,the micro-hardness tester were used to carefully analysis of the changed on surface mrcro-hardness.And the friction and wear tester were used to carefully analysis of the changed to test the friction coefficient and wear of the Al-Pb system sample surface.In addition,the electrochemical workstation was used to test and analyze the corrosion resistance of the Al-Zr system samples,and to in-depth summary of the corrosion mechanism of the alloying layer.For the Al-Pb system,the surface roughness and surface SEM analysis results show that the sample surface after HCPEB irradiation formed a typical crater morphology.The crater size was reduced even disappeared with the increase in irradiation.Also,the distribution of Pb elements tended to be uniform and rationalized,which was manifested in the progressive refinement of the lead-rich particles in the alloying layer.In addition,the surface roughness of the irradiation samples have decreased to varying degrees.At the same time,the increasing in ball milling time would affect the surface quality of the alloy after Pb alloying.With the increase of the ball milling time,the surface state of the alloy layer would gradually decrease after HCPEB irradiation.Combined with the cross-sectional morphology and EDS analysis,after treated by MA and 30 pulses of irradiation,the alloying layer about 12μm thickness with optimal surface and cross-sectional state was obtained.The alloying layer and the substrate formed a good metallurgical bond.TEM and electron diffraction results showed that after 30 pulses of irradiation,nano-scale Pb-rich particles and Al grains were obtained,and the Pb particles were evenly distributed in the Al matrix.In addition,HCPEB irradiation also induced structural defects such as dislocations and dislocation cells with extremely high density on the surface of the alloy layer,which provided a large number of channels for the diffusion of Pb atoms in the aluminum matrix.The micro-hardness showed that the surface hardness of the Al-Pb system was improved after irradiation,and the strengthening mechanisms included dislocation strengthening and fine grain strengthening.The friction and wear test results showed that after Pb alloying on the Al surface by HCPEB,the friction coefficient and wear rate of the irradiated samples were significantly reduced compared with the original ball milling and pure aluminum.With the increase of pulses number,the friction and wear properties of the alloy layer were gradually improved.This was mainly due to the formation of a nanocrystalline structure on the surface of the sample by irradiation treatment,which could effectively improve the mechanical properties.At the same time,the dispersed lead-rich nanoparticles can be used as a lubricating phase strengthening coating.In addition,the increase in the hardness of the sample surface reduces the plowing effect of the grinding ball on the coating material,thereby promoting the improvement of the wear resistance of the alloyed sample.For the Al-Zr system,X-ray diffraction analysis results showed that after HCPEB irradiation,the Zr layer pretreated by ball milling reacted with the Al matrix to produce Al₃Zr with Ll2 structure.Further microscopic analysis showed that the typical crater morphology formed on the surface of the alloying layer after HCPEB irradiation,and gradually disappeared as the irradiation process continued,but the number of craters increased sharply after 40 pulses of irradiation.This was related to the deterioration of the surface quality of the material after the energy input was too high.In addition,with the increase of irradiation pulses,the distribution of Zr elements tended to be dispersed and homogenized,and the distribution of Zr elements was the most uniform after 30 pulses.After irradiating for 30 pulses,an alloying layer of about 13μm was formed.TEM and electron diffraction results further confirmed the existence of the dispersed Ll2 intermetallic compound Al₃Zr,and the size of Al₃Zr and Al grains gradually decreased with the increase in the pulses number,which greatly promoted the improvement of the surface strength and corrosion resistance of the material.The microhardness showed that the surface hardness of the Al-Zr system material was improved after irradiation,and its strengthening mechanisms mainly included solid solution strengthening,dislocation strengthening,fine grain strengthening and second phase dispersion strengthening.Electrochemical corrosion tests showed that the corrosion resistance of pure aluminum could be improved after Zr alloying,and the electrochemical performance of sample after irradiated for 30pulses was the best.This might be related to the repassivation or self-healing of Al3Zr,an intermetallic compound,which can form a stable passivation film during the corrosion process.