Study On Microstructure And Corrosion Resistance Property Of Al-Mn-Fe-Si Alloy

In this study,the alloy Al-Mn,Al-Mn-0.15wt%Sc-0.05wt%Zr and Al-Mn-0.2wt%Sc-0.05wt%Zr were prepared,name as alloy 1#,alloy 2# and alloy 3# respectively,with different adding Sc(RE element)or Zr into Al-Mn-based alloys.The microstructure of as-cast,various thermal treatment and hot extrusion condition was analyzed.The effect of rare-earth element on microstructure and corrosion properties was exposed by electrochemical tests(including OCP,Tafel and EIS).The results show that the eutectic tissues in the matrix of as-cast alloy is significantly increased and the grain is refined with the addition of rare-earth elements,it was mainly in the form of short rodlike and spheroid,and distributed in the form of reticulation.The wight-loss immersion test presented the maximal corrosion rate was obtained by alloy 1# of free Sc and Zr.With Sc further addition,the corrosion performance is became better.The electrochemical test indicated that the most positive potential is alloy 3#,the most negative potential is alloy 1#,and alloy 3# is combined small corrosion electric current density and positive pit potential(Epit).In general,the alloy 3#(Al-Mn-0.2wt%Sc-0.05wt%Zr)showed the best corrosion resistance.After hot extrusion,the stretch orientation of grain is pratal to extrusion direction.The fine grain is obtained with the addition of Sc and Zr of the alloys.It is the main reason that the re-crystal process is inhibited by the addition of RE element.The results of corrosion immersion and electrochemical test inferred that the corrosion property of hot extrusion is improved by RE-element adding.In contrast with as-cast alloy,the extrusion alloy presented better corrosion property.The sensibility of pit corrosion and grain boundary corrosion enhanced with the thermal treatment temperature improvement.The EDS indicated that the intermetallic(Fe Mn)Al6 is transformed gradually,ascribed to the decreased resistance sensibility of grain boundary corrosion,coarse Al-point forming,inhomogeneous microstructure and increased pit corrosion.The precipitation of Al3 Sc second phase in the grain boundary with the increased thermal treatment temperature,which decreased the combined strength of grain boundary and reduced the alloy strength effect when it excess and coarse.The electrochemistry results shows that there are various corrosion behavior for different thermal treatment temperature,the susceptivity of corrosion of the alloy decreases with the increase of heat treatment temperature.And it shows the best corrosion resistance of the alloy at the temperature of 275?.