Compressive Creep Behavior and Microstructure Evolution of Al-Fe-Sc Alloy

Al-Fe alloy is a kind of high-strength and toughness aluminum alloy cable that widely used all over the world. Creep aging forming is a new forming technology，which is especially suitable for the manufacture of cables that need good elongation，and has a good development prospect. However，there are still many problems to be studied in the practical application of this technology，which should be solved urgently. Sc was an ideal rare earth element for improving thermal stability and strength of aluminum alloy. In this study，a small amount of Sc additions into Al-Fe alloy could significantly improve the compressive creep resistance，which had been lacking in other researches. In this paper，the compressive creep properties of Al-Fe-Sc alloys were studied by Axio scope A1 Zeiss me⁃ tallographic microscope（OM），electron backscatter diffraction analysis（EBSD），transmission electron microscope microanalysis （TEM）and 200HVS-5 Vickers hardness indentation technology. The effects of different compressive creep parameters on the creep be⁃ havior and microstructure of Al-Fe-Sc alloys were investigated. Compressive creep parameters were adopted as follows：compressive stress of 70 and 90 MPa，creep temperature of 90，120 and 150 ℃. It was found that the steady-state creep rate of Al-Fe-Sc alloy was 1.57×10-7，1.37×10-5 and 3.35×10-6 s-1，at compressive stress of 70 MPa，creep temperature of 90，120 and 150 ℃，and the micro⁃ hardness was HV 40.58，HV 35.16 and HV 42.32. Under the condition of 90 MPa，creep temperature of 90，120 and 150 ℃，the steady-state creep was 1.79×10-6，1.36×10-5 and 7.60×10-6 s-1，and the microhardness was HV 45.54，HV 34.46 and HV 50.34. The microstructure of samples tended to be isotropic from anisotropy with increasing temperature and pressure，and the serrated grain boundaries became more obvious. OM images showed that the grain shape of as cast Al-Fe-Sc alloy was irregular and had many fine dendritic structuresand TEM images showed that Al3Sc precipitates were dispersed at the interior subgrain and subgrain boundaries，which strongly hindered dislocation and grain boundary movement，and played a role in strengthening mechanical properties and inhib⁃ iting compressive creep deformation. Several conclusions could be drawn：（1）The steady-state creep rate of Al-Fe-Sc alloy decreases first and then increases with the increase of temperature. The steady-state creep rate of the sample at 70 MPa/150 ℃ was 3.35×10-6 s-1. In addition，with the increase of compressive stress，the steady-state creep rate of the alloy also increased.（2）The microhardness of Al-Fe-Sc alloy decreased and then increased with the increase of creeping temperature. The microhardness of the sample was the high⁃ est HV 50.34 at 90 MPa/150 ℃.（3）EBSD analysis showed that the morphology of the sample changed from anisotropy to isotropy with the increase of temperature and pressure，the "sawtooth" grain boundary became more and more obvious，and the grain size was also significantly refined. TEM images showed that Al3Sc precipitates were uniformly distributed in subgrains and subgrain boundaries，which strongly hindered the movement of dislocations and grain boundaries，and strengthened the mechanical properties of samples and inhibit compressive creep deformation.（4）Based on the main performance technical indexes and production cost of aluminum al⁃ loy wire rod，the optimal compression creep process of Al-Fe-Sc alloy was 150 ℃/70 MPa. The results showed that the addition of trace rare metal Sc significantly enhanced the creep resistance and mechanical properties of Al alloy cable.For improving the creep resis⁃ tance and mechanical properties of Al alloy cables in the future，higher content of Sc element and optimum the Sc content could be tried. On this basis，the conductivity of the sample would be measured，and both mechanical properties and conductivity could be con⁃ sidered comprehensively and selected preferentially. © 2023 Editorial Office of Chinese Journal of Rare Metals. All rights reserved.