Study On The Effect Of Zirconium Erbium And Boron On The Microstructure And Properties Of Thermal-resistant Conductive Aluminium Alloy

In order to improve the performance of aluminum conductors at high temperature,extensive work has been done by adding micro-alloying elements,such as Zirconium,Erbium,Scandium and Yttrium.Although the heat resistance is improved,the electrical conductivity is greatly reduced.Therefore,in order to maintain the comprehensive properties,the composition of alloy needs to be optimized.In previous work,our research group had optimized the composition of alloys and the heat treatment process to improve the heat resistance of Al-Zr,Al-Er and Al-Zr-Er containing trace B without decreasing the conductivity.However,the mechanisms of micro-alloying elements affecting the microstructure and properties need further exploration.In this study,we observed the microstructure and analyzed the formation mechanism of the phase with regular morphology from crystallography.The influence mechanisms of micro-alloying elements Zirconium,Erbium and Boron on the mechanical and electrical properties of the alloys were studied by testing the hardness and resistivity.The residual powders of Al-Zr-B and Al-Zr-Er-B alloys were investigated by SEM、TEM and XRD.These residual powders were found to be mainly ZrB₂ or（Zr,Er）B₂.The morphology of ZrB₂ includes hexagon,lamella and petal.Due to the composition fluctuation of hexagonal ZrB₂ during the process of growth,the corrosion resistance is different in different regions resulting in the formation of a nested structure.Although（Zr,Er）B₂ has hexagonal structure and petaloid structure,hexagonal（Zr,Er）B₂ is thicker and the petaloid（Zr,Er）B₂ is smaller in volume.In addition,there are some（Zr,Er）B₂ in the shape of hierarchical tower and corn stacked in hexagonal prisms.The factors affecting the formation of typical morphologies of（Zr,Er）B₂ were analyzed and the main factor was found to be the solid solution of Er.With a small amount of Er solid solution,（Zr,Er）B₂ is mostly hexagonal and petaloid.The increase in amount of Er solid solution led to the formation of the hierarchical tower-like structure.Further increasing the amount,（Zr,Er）B₂ become hexagonal prism structure.The as-cast alloy exhibits a coarse dendritic structure which is eliminated during homogenization annealing,but the grain size of alloy is still large.After hot extrusion,the grains are elongated along the deformation direction and tend to be fine and equiaxed.The alloy exhibits typical fibrous structure after cold rolling.The electrical conductivity and age hardening behavior of the alloys were investigated.It was found that the addition of Er and Zr reduced the electrical conductivity of the alloys,and Zr showed a more significant effect,while the addition of B reduced the adverse influence of Zr and Er on electrical conductivity.After aging heat treatment,Al-Zr and Al-Er alloys reached the hardness peaks at 175°C and300°C,respectively,meanwhile Al-Zr-Er exhibited two hardness peaks at the corresponding locations.The sufficient amount of B was added to Al-Zr,Al-Er and Al-Zr-Er alloys and formed primary ZrB₂ and ErB₂,resulting in the alloy losing the age hardening effect.However,when the amount of B in Al-Zr-Er is insufficient,the age hardening behavior of Al-Zr-Er-0.013B alloy was similar to that of Al-Er alloy,reaching the hardness peak at 300°C,indicating that B preferably reacted with Zr instead of Er.