Effects Of Rare Earth And Copper On The Structure And Performance Of 8176 Aluminum Poles

Aluminum with rare earth elements (REEs) was one of the ideal materials to replace copper to manufacture wire and cable. Adding different types and levels of rare earth elements in the conductors of aluminum alloy can play roles in desulfurization, removing oxygen and residue, refining grains and strengthening by solid solution, strengthening by second phases and so on. In this paper, the effects on the structure and performance of 8176 aluminum poles by adding rare earth and copper were explored.(1) There were the effects of modification process as 8176 aluminum poles added REEs. With the contents of REEs increased, the morphology of eutectic silicon in alloy changed from needle into short rods or granular. When the content of mixed rare earth was 0.25wt%, the honeycomb phase and white ball phase appeared. The content of Al and RE elements was highly in honeycomb phase, but the content of Si in honeycomb phase was much less than that in white ball phase. While the content of Fe in honeycomb phase was significantly higher than that in white ball phase. In this case, the resistivity of 8176 aluminum poles was from 61.5% IACS to 62.5% IACS, the lowest resistivity of the pole was 27.8 nΩ>mm2/m. And the tensile stress of 8176 aluminum poles was between 100 to 110 MPa, while those percentage elongation were about 12%.(2) With the addition of Cu, Al-Fe-Si eutectic that generated together with the primary Al phase reduced, while the number of Cu-rich second phase (CuAl2) increased. Cu mainly presents in solid solution manner in the aluminum matrix. But the number of metal bond reduced after the appearance of the second phase (CuAl2), thus the increased grain boundaries impedes the transfer of free electrons. So the resistivity of the aluminum poles increased. When the content of copper was 0.3wt%, the specific resistance of 8176 aluminum poles were from 60.0% IACS to 61.0%IACS, the lowest resistivity of the pole was 28.3 nΩmm2/m. And the tensile stress of 8176 aluminum poles was increased from 108 MPa to 119 MPa, while those percentage elongation were about 9.4%.(3) After homogenizing annealing at 500℃ for 24h, the resistivity of aluminum pole significantly decreased, because the second phase-forming elements (Cu, RE, etc.) gradually dissolved to the Al matrix. The number of grain boundaries reduced, and the free electrons relatively easy to move, so that the conductivity improved. In this case, 8176 aluminum alloy had a resistivity of 28.1 nΩmm2/m and the tensile stress of 120.4 MPa. As the increased of recrystallization annealing temperature, the resistivity of 8176 aluminum poles decreased and those tensile strength increased; While over a temperature, with the increased of recrystallization annealing temperature, the conductivity of the aluminum poles were deteriorated. While after full recrystallization annealing at 350℃ for 1h, the aluminum poles had the best properties of mechanical and electrical.