Effect Of Laser Heat Treatment On The Microstructure And Corrosion Resistance Of 7075 Aluminum Alloy

Al-Zn-Mg-Cu alloys are widely used in the aerospace industry due to the excellent mechanical properties.7075 alloy is the most typical among Al-Zn-Mg-Cu alloys.However Al-Zn-Mg-Cu alloys are very sensitive to pitting,intergranular corrosion,exfoliation corrosion,and stress corrosion cracking.The corrosion resistance of the alloy can be improved by heat treatment.In the retrogression and re-aging(RRA)treatment,the retrogression treatment with high temperature and short time is the key to improve the corrosion resistance of the alloy.The traditional retrogression time is long.The muffle furnace limits the heat treatment method.It is difficult to use the method in industrial production.It is necessary to change the heating method.The parameters of the retrogression treatment significantly affect the corrosion resistance of the alloy.The heating speed of laser is fast,and the heating time is short.It can replace the retrogression treatment of RRA.Laser retrogression and aging(LRRA)treatment was proposed.The corrosion resistance and microstructure of the 7075 alloy after RRA treatment and LRRA treatments were studied by using exfoliation corrosion test,intergranular corrosion test,polarization curve test,electrochemical impedance spectra(EIS)test,X-ray diffraction(XRD),scanning electron microscopy(SEM)and transmission electron microscopy(TEM).Treated by the LRRA treatment with the parameter of 650 W and 2 mm/s,larger ? phases are precipitated at the grain boundary.Compared with the microstructure of the alloy treated by the traditional RRA treatment,the LRRA process can increase the spacing of the grain boundary phases.The corrosion path is hard to form.The corrosion resistance of the alloy is improved.Compared with the alloy treated by RRA treatment,the sample after LRRA treatment has a higher corrosion potential and a lower current density.The EIS results show that the charge transfer resistance of the sample after LRRA treatment is increased.The charge transfer is more difficult.After the LRRA treatment(650 W,2 mm/s),the corrosion resistance of the alloy is improved.The intergranular corrosion depth is 25.3 ?m,and the exfoliation corrosion rating is EA.Compared with the alloy treated by RRA treatment,the intergranular corrosion depth is reduced by 10 ?m.It is proved that LRRA treatment can improve the corrosion resistance of the alloy.