Effect Of Sc And Er Composite Micro-Alloying On The Structure And Properties Of Al-7Mg Alloy

Al-Mg series aluminum alloys have the characteristics of high specific strength,good corrosion resistance,and excellent processing performance,and are widely used in industrial fields.Increasing the Mg content of Al-Mg series alloys is helpful to improve the strength of the alloys,but at the same time,it is easy to induce the segregation of Mg atoms and the precipitation of?phase at the grain boundaries,which adversely affects the overall properties of the alloys,especially the corrosion resistance.Microalloying has a significant effect on improving the structure of aluminum alloys and is an effective way to improve the comprehensive properties of Al-Mg alloys with high Mg content.Based on the Al-7Mg alloy,using a semi-continuous casting process the thesis prepared Al-7Mg-0.2Zr-0.3Er,Al-7Mg-0.2Zr-0.3Sc and Al-7Mg-0.2Zr-0.15Sc-0.3Er(mass fraction,%)by adding rare earth elements Sc and Er.And the ingots and plates of the three alloys were tested including hardness test,electrical conductivity test,uniaxial tensile performance test,electrochemical test,and intergranular corrosion tests and performance tests such as slow strain rate stretching,and further combined with microstructure observation techniques such as OM,SEM,TEM and EBSD to study trace the Sc and Er how to effect on the structure and properties of Al-7Mg alloys.It is expected to provide theoretical and experimental basis for further optimizing the comprehensive properties of Al-Mg alloys with high Mg content.The research results show that the addition of Sc alone and the combined addition of Sc and Er during the casting process can significantly reduce the grain size of Al-7Mg alloy ingots,inhibit the formation of dendrites and the segregation of Mg atoms,and the effect of improving the structure of the ingot is significantly better than that of alone add Er element.During the homogenization of the ingot,the secondary Al₃(Sc,Zr)particles precipitated twice are smaller in size than Al₃(Er,Zr)particles,and the distribution is more uniform,showing a better strengthening effect.In the process of stabilization annealing,Al₃(Sc,Zr)particles have stronger pinning dislocation movement and inhibiting recrystallization ability than Al₃(Er,Zr)particles.Al-7Mg-0.2Zr-0.3Sc and Al-7Mg-0.2Zr-0.15Sc-0.3Er alloy plates under the annealing conditions have a higher proportion of low-angle grain boundaries than Al-7Mg-0.2Zr-0.3Er alloy plates,so that they have more significant substructure strengthening effect and stronger mechanical properties.Corrosion resistance experiments have found that the number and distribution of?phases which have a higher corrosion potential than the aluminum matrix.So that they have important impact on the corrosion resistance of the alloy annealed sheets.Under low temperature annealing conditions,Al₃(Sc,Zr)particles are better than Al₃(Er,Zr)particles,can more effectively hinder the movement of intragranular dislocations to the grain boundaries,which not only slows down the formation of high-angle grain boundaries during the annealing process,but also can effectively inhibit the diffusion of Mg atoms through the dislocation as a channel to the high-angle grain boundary to form a continuous and coarse?phase.Continuous coarse?phase in Al-7Mg-0.2Zr-0.3Sc and Al-7Mg-0.2Zr-0.15Sc-0.3Er alloy annealed sheets,the number of?phases is small and it is discontinuously distributed in the grain boundary.So the alloy is resistant to corrosion,and the performance is better.The Al-7Mg-0.2Zr-0.3Er alloy annealing sheet has a relatively large number of?phases,presenting a continuous distribution in the grain boundary,and the alloy has weak corrosion resistance.With the continuous increase of annealing temperature,the?phase gradually re-dissolves into the matrix,and its influence on the corrosion performance is gradually weakened.At this time,the grain boundary with high potential plays a decisive role in the corrosion of the alloys.The degree of recrystallization of Al-7Mg-0.2Zr-0.3Sc and Al-7Mg-0.2Zr-0.15Sc-0.3Er alloy is relatively small,and the proportion of high-angle grain boundaries is lower than that of Al-7Mg-0.2Zr-0.3Er alloy,so it still has better corrosion resistance.