Effect Of Rare Earth Element On 7075 Alloys Mechanical Properties And The Optimization Of Retrogression And Re-aging Treatment

7075 aluminum alloys containing Ce 0.20% and Sc 0.20%(mass%)alloy were respectively prepared to investigate the effect of adding Ce and Sc on the structure and property of 7075 aluminum alloys. And adding Zr0.08% and Zr 0.18% to the0.2%Sc alloys respectively were tried to study the effect of Sc, Zr joint addition on the structure and properties of aluminum alloy. Then the combination of Sc, Zr,Ti(0.17%) adding influence on the structure and properties of 7075 alloy was also studied. The microstructure and spectroscopy of the alloys were analyzed to investigate the effects of different heat process,and the mechanical properties of alloys were also test. Furthermore, the effect of(RRA) treatment process, including the re-aging temperature and lasting time, on the 7075 aluminum alloy were aslo studied to optimize the heat treatment process. The results showed that:(1) With the Ce 0.20% added, the grain sizes is 109 um and the grain were greatly refined. After T6 aging,the tensile strength and yield strength of the alloys could increase to 583 MPa and 536 MPa,with elongation of 10%. The mechanical properties were increased by 2.28%, 3.88%, 42.86% compared with the alloys without Ce. After the RRA(465℃/2h+120℃/16h+200℃/20min+120℃/16h) treated,the above strength of the alloy were 715 MPa and 664 MPa respectively, with elongation of 10%. Compared with that of T6 states, the above Strengths improved22.64%, and 23.88% respectively with just the same elongation.(2) With the content of Sc 0.20%, the grain sizes of Sc 0.20% alloy were123 um.A13Sc was considered to be in a good interface coherency with Al matrix,which is beneficial to the improvement of the properties of the alloy. Under T6 aging,the tensile strength and yield strength of the alloys could increase to 603 MPa and560MPa, with elongation of 10%, The mechanical properties were increased by5.80%,8.53% and 42.88% when compared with the alloys without Sc. After the RRA treatment(465℃/2h+120℃/16h+160℃/20min+120℃/16h),the tensile strength were715 MPa,yield strength were 644 MPa and elongation were 10.6%respectively.Compared with the T6 states, the above properties improved 18.6%,15% and 6%.(3) The effects of combination of Zr and Sc on the properties of the alloys werealso studied. The results show that compared with that of alloys with 0.20%Zr under T6 state, the tensile strength and yield strength of the alloys with 0.18 % Zr and 0.20 Sc could increase to 630 MPa and 589 MPa, which increased 4.47% and 5.17%respectively.But after the treatment(465/2h+120℃/16h+16℃/16h+160℃/20min+120℃/16h), the properties did not change significantly.With further addition of Ti0.17 %, the tensile strength and yield strength decreased, while elongation remained the same. when addition of Sc,Zr,Ti simultaneously into the alloy, the coarse block phase Ti RE2(Al, X)20 with X being Zn, Mg or Cu, might appear. With the content of Sc + Zr increase, more massive compound might form.(4) During RRA process, the short-term retrogression might increase the solubility of solid solution elements in the matrix and accelerate the diffusion of solute atoms and vacancy rate, which might in turn promote the precipitation behavior.