Study On Modification Of Al-20Si-5Mg And Al-20Si-5Mg-0.7Ce Alloy By High Current Pulsed Electron Beam Treatment

High current pulsed electron beam(HCPEB),as a new surface modification technology,has attracted the attention of some experts and scholars for its advantages of simple operation,low surface requirements of samples,high energy utilization ratio,high repeatability and no pollution to the atmosphere.However,a large number of crater structures and microcrack will be formed on the surface of the alloy after HCPEB treatment,which limits the further industrial application of HCPEB.Some scholars found that the microcracks on the surface of Al-Si alloy can be improved by adding rare earth Nd during the HCPEB treatment.However,the elimination mechanism of crater structure is not clear.In addition,though there are many recent reports on the surface structure treated by HCPEB,few references about the influence of HCPEB treatment on the deep microstructure of treated samples are reported.In this paper,surface of Al-20Si-5Mg and Al-20Si-5Mg-0.7Ce alloys Ce were treated by HCPEB with different pulses.Effect of HCPEB treatment on surface and cross-section microstructure and properties of Al-20Si-5Mg and Al-20Si-5Mg-0.7Ce alloys were researched in detail.The results are as following:Al-20Si-5Mg alloy:SEM analysis shows that,after HCPEB treatment,a large number of craters appeared on the top surface of treated alloy;the density of crater could be reduced with the increasing number of pulses.XRD analysis shows that there is no new phase generated on the surface of alloy and all diffraction peaks shift and broaden.TEM analysis shows that a large number of nano-silicon phases were formed on the melted layer of treated alloy.A series of performance tests were carried out on the surface of alloy after HCPEB treatment with 25 pulses.It was found that after HCPEB treatment with 25 pulses:the microhardness of the Al matrix on the surface of alloy increased from 952.3 MPa of original sample to 2237.8 MPa of treated sample;the friction coefficient decreased from 0.472 of original sample to 0.274 of treated sample;the wear rate decreased from 2.2×10-3 g/m of original sample to 0.5×10-3 g/m of treated sample;Potentiodynamic polarization results show that the current density decreased from 5.288×10-5 μA/cm2 of the original sample to 3.965×10-6μA/cm2 of treated sample.In addition,the cross-sectional SEM analysis shows that the eutectic silicon structure was broken in heat affected zone.The EBSD analysis shows that the Al matrix grains in the heat affected zone were refined compared with that of the original sample;the average size of Al grains decreased from 1.412μm of original sample to 0.973 μm of treated sample.The nano indentation test shows that the nano hardness of the Al matrix in heat-affected zone was significantly improved after HCPEB treatment.Al-20Si-5Mg-0.7Ce:the primary silicon in the Al-Si-Mg alloy structure was obviously refined after addition of rare earth Ce;the density of crater structures on the alloy surface was reduced after HCPEB treatment;the crater structure was hardly found on the top surface of HCPEB-treated sample with 25 pulses.The TEM analysis shows that the nano primary silicon phase with rare earth Ce on the alloy surface is spheroidized.The EPMA analysis shows that the element distribution of the alloy surface with rare earth Ce was more uniform.In addition,a series of performance tests were carried out on the sample of HCPEB-treated Al-20Si-5Mg-0.7Ce alloy with 25 pulses.It was found that the friction coefficient of the alloy surface decreased from 0.385 of original sample to 0.213 of treated sample,the wear rate decreased from 1×10-3 g/m of original sample to 0.1×10-3 g/m of treated sample,Potentiodynamic polarization results show the current density decreased from 1.540×10-5 μA/cm2 of original sample to 1.021×10-8 μA/cm2 of treated sample.In a word,the HCPEB can refine the deep structure of Al-20Si-5Mg and Al-20Si-5Mg-0.7Ce alloy.At the same time,after adding rare earth Ce,the primary silicon on the alloy surface is spheroidized,and the wear resistance and corrosion resistance of the alloy surface are significantly improved.