Study Of Microstructure And Properties Of Zr/Er Microalloying And Severe Plastic Deformation Al-Fe Alloy

Al-Fe alloys have been widely used in cables due to the interesting combination of electrical conductivity,strength and creep resistance properties.However,the coarse and brittle Fe-containing particles act as crack initiation sites during tensile loading,which lead to deteriorated mechanical properties and reduced life-time.The most common method to reduce the negative effect of Fe-containing particles and the eutectic structures is to use rare-earth(RE)modifiers,which can improve the morphology,size and distribution of these second phases,and thus increase mechanical properties of Al-Fe alloys.However,the rare-earth modifiers are restricted due to the adverse effect of the Al-Re eutectic structures on the strength and electrical properties.Instead,Zr and Er elements can modify?-Al grains and secondary phases,and form thermal stable Al₃M precipitates with L1₂ structure,thus improving the strength and maintaining good conductivity.Further,severe plastic deformation(SPD)is a way to enhance strength and electrical conductivity of aluminum alloys.Therefore,it is of great significance to research the effects of Zr/Er microalloying and severe plastic deformation on a combination of electrical conductivity and mechanical properties of Al-Fe alloy for the development of Al-Fe alloy conductor materials.This work is focusing on the effect of Zr and/or Er on microstructure,electrical conductivity and mechanical properties of the Al-0.4Fe alloy,and the effect of SPD processing on the evolution of microstructure and properties of the Al-Fe-Zr-Er alloy.The measurements of microhardness,electrical conductivity and tensile strength,and optical microscope(OM),scanning electron microscope(SEM),electron back-scattered diffraction(EBSD),transmission electron microscope(TEM)and energy dispersive x-ray spectroscopy(EDS)were used to investigate:(1)The effect of Zr and Er on the microstructure,electrical conductivity and mechanical properties of Al-0.4Fe alloy;(2)Microstructure and property evolution in Al-0.4Fe-0.15Zr-0.25Er alloy processed by high pressure torsion;(3)The effect of equal channel angular pressing on the microstructure,electrical conductivity and mechanical properties of Al-0.4Fe-0.1Zr-0.2Er alloy;(4)The characterization of structural defects in severe plastic deformation Al-Fe-Zr-Er alloy and their formation mechanism was analyzed.The following conclusions can be drawn:(1)Zr addition refines grain size of the Al-0.4Fe alloy owning to fine Al₃Zr particles acting as nucleation sites,while Er does not.Both Zr and Er modify the morphology of Al₃Fe phases,which change from needle-like to fine short rod particles.(2)Zr and Er could improve recrystallization resistant capability of the Al-0.4Fe alloy.The effect of Zr is more pronounced than Er,and the synergetic effect of Zr and Er is more significant than the single addition due to the thermal stable Al₃(Zr,Er)precipitations,which can pin the movement of dislocations.Zr and Er additions could increase microhardness and strength,but with a slight reduction in electrical conductivity.The best combination of strength and conductivity is obtained in alloy A3(Al-0.4Fe-0.2Er)after cold rolling:a yield strength of 145 MPa,elongation at fractureof8%and electrical conductivity of 61.2%IACS.(3)The microstructure from center to edge of Al-0.4Fe-0.15Zr-0.25Er alloy deformed by HPT for 0.25,0.5 and 1 turn is inhomogeneous,while a homogeneous microstructure can be obtained after 5 turns and beyond.The grains are refined to 600nm from 40?m after 5 turns HPT.The microhardness of Al-0.4Fe-0.15Zr-0.25Er alloy increases with increasing HPT strain,and the maximum value of 60 HV is obtained at a strain about 12.Then the microhardness decreases slightly to a steady stage(?50 HV)after 5 and 20 turns HPT.(4)HPT processing could accelerate dissolution of the Al₃(Zr,Er)particles resulting in a supraturated solid solution with high density defects.The Al₃(Zr,Er)precipitates can be formed at 150°C due to high density of lattice defects introduced by HPT.(5)ECAP processing could effectively refine the grains of Al-0.4Fe-0.1Zr-0.2Er alloy.The mixed structure with micron and nanocrystalline grains is obtained in samples deformed by ECAP for 4 passes,and dynamic recovery and recrystallization can occur.The microhardness and strength increase with increasing ECAP passes,while the elongation and conductivity decrease first and then increase.The best properties are obtained in the alloy deformed by ECAP for 4 passes:yield strength of 183 MPa,elongation of 16%,and conductivity of 51.3%IACS.(6)Stacking faults and nanotwins are observed in the Al-Fe-Zr-Er alloy deformed by HPT and ECAP.The stacking faults are derived from the 0°screw dislocation decomposition resulting in two Shockley dislocations.The nanotwins are from the dynamic overlapping of stacking faults.These stacking faults and nanotwins still exist after annealing at 400°C.Full dislocations are observed near nanotwins due to the pinning effect of nanotwins on the full dislocation.(7)“Z”shaped nanotwins are observed in Al-Fe-Zr-Er alloy deformed by ECAP,and the included angle of the adjacent twins on different slip planes is 109.5°.This is caused by Shockley dislocations reaction,which could generate 1/3[110]dislocation lock.