The Effect Of Ultrasonic Peening Treatment On Residual Stress Field And Corrosion Resistance Of AlSi10Mg Components Fabricated By SLM

As an advanced digital manufacturing technology with rapid development,additive manufacturing has its advantages including short manufacturing cycle,material saving,and complexity for free,and can directly form metal parts with arbitrarily complex structures and good performance.Therefore,it has great potential for application in marine and offshore engineering.The continuous rapid melting and solidification during the AM processing result in internal residual stress generated in the parts.This will lead to the deformation and cracking of the parts in the process of forming.It will also reduce the mechanical properties of the formed parts and the stress corrosion resistance of the parts in the marine environment.It is a long-term restriction to the extensive use of metal components fabricated by additive manufacturing technology.Many experts and scholars expressed great enthusiasm for improving the stress corrosion cracking resistance of parts in additive manufacture.Ultrasonic peening treatment(UPT)has been proved to be an effective way of eliminating residual stress in weld structures.Thus,it shows a great potential in stress relief for metal parts fabricated by additive manufacturing technology.Compared with other treatment processes,UPT has the advantages of flexibility,convenience,environmental protection and low cost.In this paper,an investigation into the ultrasonic treatment process of AlSi10Mg specimens fabricated by selective laser melting(SLM)process is conducted by means of experiment and numerical simulation.The specimens are prepared using a SLM machine,and UPT on their top surface is carried out.The residual stresses are measured with a X-ray stress diffraction device before and after UPT.By UPT,the trend of reducing the residual stress of as-fabricated components is revealed.In the process of UPT,the contact time between impact needle and specimen is very short,and the contact time period of single impact is only micro or even milliseconds.The impact between impact needle and specimen belongs to the process of high-speed transient non-linearity.The parameters of impact force,contact area and pressure distribution are difficult to predict by experimental and theoretical methods.So,a finite element simulation method for analyzing the influence of UPT on the residual stress field of SLM fabricated specimens is proposed and validated by experiments.Firstly,the thermal mechanical coupling numerical simulation of the SLM process of the specimen is carried out in order to obtain the residual stress distribution in the as-fabricated specimen.Then,the transient dynamic finite element simulation model of the UPT process of the specimen is established,and the UPT effect analysis is implemented.In the UPT simulation,the residual stress is applied as a pre-stress on the specimen,and the specimen’s material mechanical property is described by the Johnson-cook model,whose parameters are determined by Split Hopkinson Pressure Bar(SHPB)experiment.The effect of UPT equipment parameters on stress field of AlSi10Mg aluminum alloy samples fabricated by SLM was studied.The numerical simulation model of the Ultrasonic Peening Treatment on Residual Stress Field of AlSi10Mg Aluminum Alloy Components Fabricated by SLM of the experimentally verified calculation results is used as a research tool.The stress field of the component was analyzed by choosing different impact frequency,amplitude and time,so as to determine the influence of ultrasonic peening parameters on the stress field of laser selective melting AlSi10Mg aluminum alloy component.Meanwhile,the impact velocity-time curve and displacement-time curve of the impact needle are extracted,and the mechanism of the impact frequency and amplitude on the stress field is analyzed.The electrochemical corrosion experiments of AlSi10Mg alloy specimens fabricated by SLM before and after UPT were carried out.The polarization curves and electrochemical impedance test Nyquist curves of the specimens were obtained.The analysis of polarization curves and electrochemical impedance test Nyquist curves showed that UPT can improve the stress corrosion resistance of AlSi10Mg alloy components formed by SLM.Scanning electron microscopy(SEM),hardness and X-ray diffraction(XRD)were used to test the samples before and after UPT,and the mechanism was analyzed.