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Effect of Thermomechanical Treatment of Al-Zn-Mg-Cu with Minor Amount of Sc and Zr on the Mechanical Properties
Authors:Azam Beigi Kheradmand  Shamseddin Mirdamadi  Zahra Lalegani  Bejan Hamawandi
Affiliation:1.Department of Mechanical Engineering, Shahrekord Branch, Islamic Azad University, Shahrekord 88137-33395, Iran;2.Department of Materials Engineering, Science and Research Branch, Islamic Azad University, Tehran 82448-65179, Iran;3.Young Researchers and Elite Club, Shahrekord Branch, Islamic Azad University, Shahrekord 88137-33395, Iran;4.Department of Applied Physics, KTH Royal Institute of Technology, SE-10691 Stockholm, Sweden
Abstract:In this study, the mechanical and microstructural properties of Al-Zn-Mg-Cu-Zr cast alloy with 0.1% Sc under homogeneous, dissolution, and T6 and thermomechanical treatments with the aim of increasing the volume fraction of MgZn2. Al3(Sc,Zr) reinforcing precipitates were examined by hardness, microscopic examinations, tensile tests and software analysis. The results showed that, firstly, the hardness results are well proportional to the results of the tensile properties of alloys and, secondly, the strength of the alloy with thermomechanical treatments compared to T6 treatments increased from 492 MPa to 620 MPa and the elongation increased from 8% to 17% and was 100% upgraded. Microstructural and fracture cross section investigations showed that Al3(Sc,Zr) nanosize dispersoids were evenly distributed among MgZn2 dispersoids and the alloy fracture was of semi-ductile type and nanosize dispersoids less than 10 nm were observed at the end of the dimples in the fracture section. The volume fraction of nanosize dispersoids in the whole microstructure of thermomechanical treatment samples was also much higher than that of T6 heat treated samples, so that the percentage of Al3(Sc,Zr) precipitates arrived from less than 1% in T6 operation to 8.28% in the quench-controlled thermomechanical operation (with 50% deformation). The quality index (QI) in thermomechanical treatment samples is 19% higher than T6 samples, so that this index has increased from 641 in T6 operation to 760 in samples under thermomechanical treatment due to precipitate morphology, volume fraction of precipitates, their uniform distribution in the matrix, and nano sized precipitates in samples under thermomechanical treatment.
Keywords:scandium   thermomechanical treatment   microstructure   7000 series alloy
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