Effects Of Sc And Zr Addition On Microstructure And Mechanical Properties Of Al-3Cu-2Li Alloy

Al-Li alloy has been extensively used in the field of aerospace because of low density,high elastic modulus,high specific strength and high specific stiffness,low fatigue crack growth rate,good high/low temperature properties and weldability.Rare earth alloying is an effective way to further improve the performance of Al-Li alloy.The addition of Sc into Al-Li alloy can result in grain refinement,increase of recrystallization resistance and dispersion strengthening.However,the high price of Sc limits its widely application in Al-Li alloy.Zr,as another efficient and common alloy element,can serve as a good candidate to partially instead of Sc.Accordingly,the research about composite alloying with Sc and Zr is very important to obtain low cost and high performance Al-Li alloys.In this work,different contents of Sc and Zr were designed on the basis of Al,3Cu-2Li alloy.The microstructure and mechanical properties of the alloys in different states of casting,homogenization,rolling,annealing,solution and aging were researched.The effects of the additions of Sc and Zr in Al-3Cu-2Li alloy on the microstructure and mechanical properties were investigated.The results show that,composite addition of Sc and Zr in Al-3Cu-2Li alloy causes the formation of primary Al₃?Sc,Zr?particle which plays an important role in grain refinement.It also serves as a main strengthening phase,like the phases of ?' and T1 in the alloy.The co-planar slip is reduced because of it and the strength of alloy was improved obviously.With the increase of Sc and Zr content,grains are refined.The alloy of Al-3Cu-2Li-0.2Sc-0.2Zr possesses the fine grains with an average grain size of 24.2?m.The hardness of the alloy is 119.2HV,and tensile strength is 257MPa.Compared with the alloy without Sc and Zr,the hardness and tensile strength of Al-3Cu-2Li-0.2Sc-0.2Zr increase by 18.8%and 52.9%,respectively.After T6?480?/45min water quenching+165?/20h?processing,the hardness is 174.1HV and tensile strength is 488MPa.In Al-Cu-Li-Zr-Sc alloy,the refining strengthening effect is derived from the primary Al₃?Sc,Zr?particle.The secondary Al₃?Sc,Zr?can effectively inhibit recrystallization behavior during deformation.Deformation strengthening can be attributed to the grain sliding and dislocation tangles during hot rolling,annealing and cold rolling.Deformation strengthening causes the increase of strength and hardness,the decrease of plasticity.After solid solution treatment at 480?/45min,most of the second phases of the alloy are dissolved into the matrix,and the plasticity is improved obviously.After solid solution treatment at 480?/45min,the elongation of Al-3Cu-2Li-0.1Zr-0.1Sc alloy is 16.5%.The precipitation strengthening during aging treatment can be attributed to the precipitations of Al₃Li,Al₂CuLi and secondary Al₃?Sc,Zr?.In summary,grain refinement strengthening,deformation strengthening,solid solution strengthening and precipitation strengthening were the main reinforcement mechanisms in the Al-Cu-Li-Zr-Sc alloy.