Effect Of Cu, Si And Heat Treatment On The Properties Of Al-Si Alloys

Abstract:The present situation and the application in the power system of aluminium alloy were mainly described in this paper. The factors that affect electrical and mechanical properties of Al-Si alloy were analyzed. The effects of alloy elements and the process of heat treatment on the mechanical properties and electrical conductivity were studied deeply.The effects of the content of Cu, Si elements on the mechanical properties and electrical properties of Al-Si alloys were investigated by Wheatstone Bridge Conductivity Measurement, Optical Microscope, Scanning Electron Microscope and X-Ray Diffraction Analysis. The results indicated that increasing the content of Si and Cu decreased the conductivity of Al-Si alloy; when Si content was larger than its solubility in Al, variation of Si content has little influence on the lattice constant, the resistivity of Al-Si alloy are determined by the volume percentage of Si; when Cu content was within its solubility in Al, the increase of Cu content would increase the distortion of aluminum lattice, consequently, the influence of Cu can be estimated according to Al lattice constant deviation; When Si change between7%and12.8%, the hardness of alloy increase with increasing Si content, but the tensile strength of near eutectic point rise slow; When the Si content is fixed at9.8%, the Cu content is between zero and3%, with the increase of Cu content, the tensile strength and hardness of the alloys increase with the increasing of Cu content.The optimized heat treatment process of Al-9.8%Si-3%Cu alloy were determined by orthogonal experimental design as followings, the temperature of solid solution treatment is520℃, the time of solid solution processing is5h, the temperature of artificial aging is180℃, the time of artificial aging is10h. The property of alloy under this condition was determined as followings, the electrical conductivity is38.02%IACS, the thermal conductivity is166.72w/m·k; the tensile strength is246.5MPa, the brinell hardness is87.1HB. After heat treatment, Al2Cu phase precipitates from the supersaturated aluminum solid solution, the degree of lattice distortion decreases obviously, therefore, the electrical conductivity of alloy increased remarkablely, the maximal increasement is up to26.48%. After heat treatment process, the eutectic Si phase begin fusing and got a degree of balling in Al-9.8%Si-3%Cu alloy, Al2Cu phase precipitates from supersaturated aluminum solid solution in forms of small and diffuse phase during the artificial aging process, the mechanical properties of alloys are improved obviously, the strength ratio is10.54%, the hardness increased by8.33%.