The Effects Of Minor Alloying On The Microstructure And Mechanical Properties Of Al-Cu-Mg Alloy

The recent development trend of Al-Cu-Mg alloys at home and abroad was reviewed, as well as the application of minor elements Sc and Zr in the aluminum alloys. In this thesis, by adding the trace elements of Sc and Zr into the Al-4Cu-1.5Mg alloy, the effects of Sc addition, Zr addition and combination of them on the microstructure and mechanical properties of the Al-4Cu-1.5Mg alloy were studied, and the heat treatment methods for Al-4Cu-1.5Mg-0.2Zr, Al-4Cu-1.5Mg-0.5Sc, and Al-4Cu-1.5Mg-0.4Sc-0.2Zr alloys were experimentally investigated.The experimental results indicate that as far as the Sc addition is individually concerned, the refinement result of the Al-4Cu-1.5Mg alloy with 0.5% Sc addition is comparatively better. The tensile strength and yield strength of the alloy is 260.0MPa and 183.8MPa, respectively, while the elongation of the alloy is up to 3.6%. The main strengthening phases of the alloy isθ(Al2Cu) and S(Al2CuMg), and the element of Sc is fundamentally in the form of solid solution. As far as the Zr addition is individually concerned, the refinement result of the Al-4Cu-1.5Mg alloy with 0.2% Zr addition is comparatively better. After adding 0.2%Zr, the tensile strength and yield strength of alloy are respectively up to 214.1MPa and 178.5MPa, while the elongation of the alloy is up to 3.2%. A part of Zr element is solved in theα-Al matrix, and the other is formed to be the phase of Al3Zr, as the nucleus of heterogeneous nucleation, effectivelly improving the dendrite structure and mechanical properties of the alloy. Sc and Zr compound alloying has a strong role in the refinement of the as cast microstructure of Al-4Cu-1.5Mg alloy. When 0.4%Sc and 0.2%Zr are compound added, the refinement result of the alloy is better, and the mechanical properties of the alloy are obviously improved. The tensile strength, yield strength and elongation rate of the alloy are the best. Compared with the original alloy containing no Sc and Zr, the tensile strength is increased by 55.3%, and the elongation rate is increased approximately three times. Apart from solving in the solid solution ofα-Al, the minor Sc and Zr are formed to be the particles of Al3(Sc,Zr) phase.The experimental results show that the heat treatment method of the Al-4Cu-1.5Mg-0.2Zr alloy is determined as 420℃×8h+490℃×16h(homogenization)+493℃×20min(solid solution)+water quenching+165℃×2h(aging). After heat treatment, the tensile strength and yield strength of the alloy are raised 84.5% and 79.3%, respectively. The homogenization treatment methods of the Al-4Cu-1.5Mg-0.5Sc and Al-4Cu-1.5Mg-0.4Sc-0.2Zr alloys are determined as 350℃×8h+490℃×16h and 420℃×8h+490℃×16h, respectively. After homogenization treatment, these two alloys are subsequently treated as 493℃×20min (solid solution)+water quenching+165℃×2h(aging). After heat treatment, the mechanical properties of the two alloys are effectively improved. The tensile strength and yield strength of Al-4Cu-1.5Mg-0.5Sc alloy are raised 50% and 30.6%, respectively, while the elongation rate is increased six times. The tensile strength of the Al-4Cu-1.5Mg-0.4Sc-0.2Zr alloy is raised 45.5%, and the elongation rate is doubled.