Study On Effect Mechanism Of Element Modification On Electrical Conductivity Of Mn-containing Aluminum Alloys

With the development of electric power and communication technologies,the application of high electrical/thermal conductivity aluminum alloys is in increasing demand.Manganese is the one of the most widely alloying element existed in commercial aluminum alloys,but it seriously deteriorates the electrical and thermal conductivity properties of aluminum alloys.Therefore,how to inhibit the negative effects of Mn on conduction while ensuring the favorable effect of Mn deserves attention.In this paper,the influences of element types on the electrical conductivity of pure aluminum and their mechanisms were systematically studied and discussed.The better modification process was optimized to improve the electrical conductivity based on the modification of elements to regulate the microstructure of Mn-containing aluminum alloys.The results show that different types of alloying elements cause the conductivity of pure aluminum to decrease to different extend.The influences of the solution type elements are mainly affected by the atomic radius differences between the solution atom and Al,the valence differences,the electron distribution outside the nucleus and the solidification reaction types.For the transitional elements,such as Mn,the valence differences between them and Al are more than or equal to 3,and the solidification reactions between Al and the transitional elements are peritectic reaction with a large number of electron vacancies in the outer layer.Those are the main reasons significantly reducing the conductivity of pure aluminum.For Al-0.4Mn alloys,the electrical conductivity is improved by up to 6.8%or 3.5%after modification with B or Y.In contrast,the electrical conductivity of the Al-0.4Mn alloy modified with a combination of B and Y is improved by 8.9%,which is better than that of the single elemental modification.For the Si-containing aluminum alloy systems,Al-1Si-0.4Fe-0.4Mn and Al-7Si-1Fe-0.4Mn alloy,their electrical conductivity are enhanced by up to 21%and 21.3%after the B and Y composite modifications,respectively.In the Si-free aluminum alloy systems,the modification effect of boron is significantly better than that of yttrium.Element B promotes the precipitation of Mn elements in the aluminum matrix through boron treatment and the formation of doped borides,resulting in a significant enhancement of the electrical conductivity of the aluminum alloy.For Si-containing aluminum alloy systems,the modification effects of yttrium on aluminum alloys increases with increasing Si and Fe contents.In the Al-7Si-1Fe-0.4Mn alloys,the enhancements of electrical conductivity by yttrium are better than that by boron.On the one hand,element Y adsorbs on the growth front of the eutectic Si phase and transforms the slate-like Si phase into a coral-like one.Also,the long needle-like Fe-rich phase and the Chinese character Al₁₅(Fe,Mn)₃Si₂ phase were remarkable refined.On the other hand,element Y also promotes the precipitation of the Al₂Si₂Y phase,which further improves the electrical conductivity of the alloys.It is worth noting that the Mn and Y elements are adsorbed by Al B₂ to form the Al₁₀Mn₂Y phase when B and Y elements are compounded to modify the Al-Si-Fe-Mn alloys,while part of the Y elements maintain their modification of the Si phase.The above two mechanisms synergistically enhance the electrical conductivity of the aluminum alloys.In this paper,the mechanisms underlying the effects of alloying elements and modification treatments on the electrical conductivity of aluminum alloys are investigated.An effective way to inhibit the rapid reduction of the electrical conductivity of aluminum alloys by Mn elements is obtained.The method is applied to commercial aluminum alloys to improve their electrical conductivity,confirming the suitability of the combined modification of B and Y elements to improve the electrical conductivity of commercial Mn-containing aluminum alloys for industrial applications.