Influence Of Second Phases On Electrical Conductivity And Mechanical Properties Of Aluminum Alloys

Al alloys are playing more and more important roles in overhead power transmission and other electrical conductor applications, which have high demands of both tensile strength and electrical conductivity. However, the effect of second phases on electrical conductivity of the alloys remains unclear, thus it is necessary to conduct further detail research in this field.The present work researched the influence of Fe on the electrical conductivity and mechanical properties of Si-containing Al alloys, mainly focusing on the formation of Fe phases and their compositions, morphologies and distributions in Al alloys. The formation of Mg2Si during heat treatment process of 6063 alloy was studied to discuss its influenceon the electrical conductivity. In addition, influence of Al3BC particles on the electrical conductivity and mechanical properties of 1070 alloy was also studied.The major research results of the present work are as follows:(1) Influence of Fe on the electrical conductivity and mechanical properties of pure AIIt is revealed that the electrical conductivity of pure Al (99.999wt.%) is significantly decreased when 0.1wt.% Si is added. However, if a certain content of Fe was also added in the Si-containing pure Al, electrical conductivity of the alloy is improved due to the formation of a-Al8Fe2Si phase during solidification. In addition, the a-Al8Fe2Si phase evolves to spherical morphology after a long time and high temperature homogenization treatment, meanwhile the tensile strength and electrical conductivity of the alloys can also be obviously improved. It was found that the phase evolution is related to the diffusion of Fe and Si, and the time can be reduced if a higher homogenization temperature was applied or a certain amount of grain refiner was added in the alloy.(2) Second phases in Al-Mg-Si alloy and their influence on the electrical conductivity and mechanical propertiesIt is revealed that both the electrical conductivity and tensile strength of Al-0.5Mg-0.35Si alloy improve along with the ageing treatment procedure. In addition, under a given ageing condition, electrical conductivity of the alloy improves with the increase of solid solution temperature, while the electrical conductivity decreases with aging temperature after solution treatment.When a certain content of Fe is added into the Al-0.5Mg-0.35Si alloy, a-Al8Fe2Si phase formed during through a ternary eutectic reaction. The electrical conductivity of the alloy was improved since the Si atoms are bonded by Fe, restricting it to dissolve into the Al matrix. As a contrast, the Brinell hardness and UTS25℃of the alloy were significantly decreased, while the mechanical properties of the Al-0.5Mg-0.35S-0.2Fe alloy were improved with a certain addition of extra Si element.Electrical conductivity and mechanical properties of the Al-0.5Mg-0.4S-0.2Fe alloy were both improved after homogenization treatment. It is supposed that the attractive performances can be attributed to the evolution of a-Al8Fe2Si ternary phases. In addition, compared to the Al-0.5Mg-0.35Si alloy, the tensile strength of Al-0.5Mg-0.4Si-0.2Fe alloy at 300℃ was improved from 150MPa to 175MPa.(3) The synergistic effect of Al-8B-2C master alloy on the conductivity and strength of 1070 alloyThe UTS25℃of 1070 alloy was increased by 43.9% and the electrical conductivity by 0.8% IACS with the addition of 3wt.% Al-8B-2C master alloy. The strengthening of the alloy was assumed to the mutual contribution of dispersion strengthening and fine-grain strengthening of AI3BC particles. Meanwhile, the tiny enhanced resistance due to Al3BC particles can be offset by AlB2 particles in Al-8B-2C master alloy because of the inoculation of transition elements.