| Abstract:The effect of Sn or Sn and Ag additions on the properties by Vickers hardness testing、tensile strength testing、fracture toughness testing and microstructure observed by scanning electron microscopy(SEM)、transmission electron microscopy(TEM)、optical microscopy (OM) on the Al-Zn-Mg-Cu alloy were studied. The results are listed as follows:(1)The microstructure as-cast Al-Zn-Mg-Cu alloy with addition of Sn or Sn and Ag are refined, and can form the Mg2Sn phase. This new phase can remain during later hot treatment.(2) The Al-Zn-Mg-Cu alloy with Sn addition has faster ageing respond speed and longer time to reach peak ageing (34h,44h respectively) and slower hardness decrease speed during overaged duration aged at120℃. Meanwhile, the ultimate tensile strength(UTS) and yield strength(YS) of the Al-Zn-Mg-Cu-Sn are515MPa、468MPa respectively, which are enhanced compared with the Al-Zn-Mg-Cu alloy (504MPa,441Mpa).(3) Addition of Sn can reduce the depth of the intergranular corrosion, decrease the corrosion current density, improve the exfoliation corrosion morphology, so enhance the corrosion properties of the Al-Zn-Mg-Cu alloy.(4) The Al-Zn-Mg-Cu-Sn-Ag alloy has faster ageing respond speed, shorter time to reach peak ageing (34h,24h respectively) and slower hardness decrease speed at overaged duration aged at120癈, and has even finer aged grain morphology thus strengthen the tensile strength (529MPa,493MPa respectively).(5) The corrosion property of Al-Zn-Mg-Cu-Sn-Ag alloy is increased because of the formation of Mg2Sn phase and more discontinuous coarser grain boundary precipitates. However, the narrower PFZ and the interaction between Ag and Mg atoms made the corrosion property of Al-Zn-Mg-Cu-Sn-Ag is bad to the Al-Zn-Mg-Cu-Sn alloy, but is better than that of Al-Zn-Mg-Cu alloy. (6) The fracture toughness of the Al-Zn-Mg-Cu-Sn alloy and Al-Zn-Mg-Cu-Sn-Ag alloy is close to that of Al-Zn-Mg-Cu alloy, has no obvious decrease. |
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