| Al-Zn-Mg alloy is a typical medium and high-strength alloy,which has the advantages of wide quenching range,good formability,good processing performance and welding performance.Widely used in the high-speed train industry.However,the working environment of high-speed rail trains is very complicated.Because the structural parts and railway components of the train are often exposed to the Cl-environment,local corrosion will be caused,which poses a huge threat to the safety of long-term trains.This research studies the effect of Mn on the microstructure,hardness,corrosion resistance and wear properties of Al-7.02Zn-2.6Mg alloy.Two-stage aging treatment was performed on the alloy to study the effect of pre-aging temperature and time on the alloy structure and hardness,and further study the effect of pre-aging treatment（105℃×xh）+final aging treatment（160℃×8h）on alloy structure and hardness,corrosion resistance and wear performance.The main conclusions are as follows:（1）With the Mn content increases from 0%to 0.45%,the cast Al-7.02Zn-2.6Mg alloy grain size first decreases and then increases.During the solidification process,Mn will generate dispersed Al6Mn phase.When the content of Mn is 0.35%,the refinement of the alloy structure is most obvious.The eutectic phase of Al-7.02Zn-2.6Mg-0.35Mn alloy is dissolved after heat treatment;when the pre-aging treatment（105℃×8h）+final aging treatment（160℃×8h）,there are uniform and fine Mg Zn2′and coarse and intermittent Mg Zn2 phases at the grain boundary on the substrate.（2）The hardness of Al-7.02Zn-2.6Mg alloy is increased by adding Mn element.The hardness of Al-7.02Zn-2.6Mg alloy reaches the highest value of 114.1Hb with the addition of0.35%Mn,which is 13.3%higher than that of the alloy without Mn element（100.7HB）.The Al-7.02Zn-2.6Mg-0.35Mn alloy exhibits double"peak"hardening with the prolongation of pre-aging time at 105℃.When the pre-aging time is 4h,the highest hardness value is 176.8HB,and when the pre-aging time is 8h,the hardness value is 173.9HB,which is the second highest value.（3）The order of corrosion current density of alloys with different Mn content is1#alloy>2#alloy>5#alloy>3#alloy>4#alloy.The corrosion current density of the alloy without Mn is 16.05μA·cm-2.The corrosion current density is 7.713μA·cm-2 When the Mn content is 0.35%,which shows the best corrosion resistance.The corrosion current density decreased from23.600μA·cm-2 to 7.490μA·cm-2 when the pre-aging time was 0h～8h,and rose to 8.600μA·cm-2from 8h to 12h.The alloy with a pre-ageing time of 8h has good corrosion resistance.（4）The addition of Mn can improve the wear resistance of Al-7.02Zn-2.6Mg alloy.With the increasing of Mn content,the wear decreases firstly and then increases.The highest wear rates of the alloy without Mn are 1.47mg·cm-2 and 2.00mg·cm-2,respectively.When adding0.35%Mn,the lowest wear rates are 0.93mg·cm-2 and 1.56mg·cm-2,respectively.With the prolongation of pre-aging time,the wear rate presents a double"valley"type change,and the wear rate at 4h is 0.71mg·cm-2 and 1.07mg·cm-2,respectively,with the lowest wear rate and the best wear resistance.The wear rates were 0.80mg·cm-2 and 1.24mg·cm-2 at 8h,respectively.The wear resistance was good.The paper has 47 pictures,7 tables,and 92 references. |
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