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.
Highlights
Aluminum (Al) alloys are widely used in various industries
Considering that the purpose of this study was to increase the volume fraction of precipitates and their uniform distribution using thermomechanical treatments, MIP software v4 was used to calculate the volume fraction of precipitates created in thermomechanical treatments and the results are compared with the volume fraction of precipitates from T6 treatment
The results show that the tensile strength of the alloy containing 0.1%Sc with thermomechanical and ageing treatments has increased by 25% compared to the alloy under T6 treatment, so that the tensile strength of the alloy has increased from 490 MPa to 620 MPa
Summary
Aluminum (Al) alloys are widely used in various industries. The addition of rare earth elements to Al alloys has been proven to have optimal effects [1,2,3,4,5,6,7]. The combination of alloying and the addition of elements, such as Sc, and plastic deformation and heat treatment to control these precipitates or particles during thermomechanical processing, can dramatically affect the microstructure evolution of Al-Zn-Mg-Cu alloys to modify grains and improve their properties. Adding elements such as Sc to this group of alloys and combining the resulting properties with the properties obtained from thermomechanical treatments creates Al3Sc particles. Because Zr is another effective and well-known alloying element that reduces the average grain size and improves the tensile strength by forming the Al3Zr particles [39]
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