Effects Of Sc And Zr Microalloying Additions On The Microstructure And Properties Of Al-Cu-Mg Alloys

Al-Cu-Mg alloys have been widely used for structural applications in the automotive,marine,construction and aerospace industries due to their low density,high strength and good forming process ability.More and more demands have been put forward with the continuous development of new technology.Rare earth element Sc is the most effective micro-alloying elements to modify the microstructure and improve the performance of Al alloys,but its high cost limits the extensively application.This research adopts combining addition of Sc and Zr,and investigates the effect of Sc/Zr ratio on microstructure and properties of Al-Cu-Mg alloys in order to achieve the purpose of reducing the cost and improving their performance.In this work,through homogenization treatment,rolling deformation,solid solution treatment and aging treatment,the effects of Sc+Zr addition amount on the microstructure and mechanical properties of Al-Cu-Mg alloys were investigated;Adopting composition test of grain boundaries precipitates,inter-granular corrosion test,polarization curve test,the calculation of tensile properties loss rate before and after corrosion and observation evolution process of cross section morphology of inter-granular corrosion,the effects of different Sc+Zr addition on the microstructure and corrosion properties were investigated;In order to further improve mechanical properties of Al-Cu-Mg alloys,two-stage homogenization treatment and pre-deformation have been employed.Furthermore,the mechanism of the Sc and Zr elements on improvement of mechanical properties and corrosion resistance were also investigated.The results show that the addition of Sc with Zr could eliminate dendritic structure in the as-cast alloy,refine grains size,inhibit recrystallization behavior and improve the tensile properties of the alloys.Al-Cu-Mg alloy has the good comprehensive mechanical properties with 0.1wt.%Sc and 0.2wt.%Zr additions.Through two-stage homogenization treatment,rolling deformation,solid solution treatment,30%pre-deformation and aging treatment,Al-4.0Cu-2.0Mg-0.1Sc-0.2Zr alloy acquires excellent comprehensive mechanical properties,?_b=588 MPa,?_s=560MPa,?=9.6%,yield ratio up to 0.95.Compared to Al-4.0Cu-2.0Mg-0.1Sc-0.2Zr alloy subjected to single-stage homogenization treatment,rolling deformation,solid solution treatment and aging treatment,?_b increased by 34.9%,?_s increase by 67.7%and yield ratio from 0.76 increase to 0.95.Adding trace of Sc and Zr makes grain boundary precipitate phases discontinuous distribution,and increases the content of Mg and Mg/Cu ratio in grain boundary precipitate phases.The cross section morphology of inter-granular corrosion transforms from the original surface corrosion holes small,internal corrosion serious"undercut"into"ellipse",so as to improve the corrosion resistance of Al-Cu-Mg alloy.