| Focusing on the demand to domestically produce aluminum alloy rod used in high power device, the composition, structure, properties and fabrication technology of the aluminum alloy with high strength and conductivity were investigated. Based on the study of original products, laboratory study and trial-production, the chemical composition range of the aluminum alloy was determined and research on casting of ingots, homogenization treatment, hot extrusion, solution treatment and quenching, control of low residual stress and ageing treatment on the alu minum alloy were conducted thoroughly. The relationship of fabrication technology, structure and properties was studied with analysis methods such as optical microscopy(OM), scanning electron microscope(SEM), transmission electron microscope(TEM), X-Ray diffraction(XRD), differential scanning calorimeter(DSC).The results showed that: the main alloy content are as follows, Zn: 6.0~6.4wt%,Mg: 2.0~2.3wt%,Cu: 1.6~1.9wt%,Cr: 0.1~0.2wt%,Mn: 0.2~0.4wt%. The main microstructure of the casting aluminum alloy is dendrite, and the lamellar non-equilibrium eutectic between different dendrites is Al Zn Mg Cu phase as well as a small amount of Fe-rich phase. The round ingot fabricated by DC casting has fine shape and homogeneous microstructure, and both the size and amount of precipitated phase is small.Homogenization treatment of the aluminum alloy was studied, and the treatment technique is determined as 460~470 ℃ for 24 h. After homogenization treatment, the Al Zn Mg Cu phase dissolute back to the matrix, and a certain amount of Fe-rich phase still exists. During the cooling process of the sample after the solution treatment, a great amount of micro-sized Mg Zn2 phase were appeared because of desolventizing.Thermal simulation test was adopted to study the flow behavior of the aluminum alloy. And combined with the production procedure, the process parameters of the hot extrusion were determined. The process temperature is 380~430 ℃, while the temperature of the extrusion mold is 400~450℃, the extrusion speed is 0.1~0.3mm/s and the extrusion coefficient is 17.8. High quality extrusion with fine appearance and homogeneous rods are fabricated.Solution treatment technique was investiga ted. The former homogenization treatment is proved to be optimal, so single-stage solution treatment was adopted. The solution parameters are 470~475 ℃ for 75 min. The aluminum alloy was arranged by stretching straightening timely, accurate transfer roller, and with two roller straightening method repeatedly after the solution treatment, to guarantee the rod material with low residual stress and flatness control.The research on aging process showed that single-stage aging and two-step aging cannot meet the requirements. Thus a novel three-step aging treatment was applied, which is: 120℃/22 h + 170℃/90 min, then water cooling and followed by 120℃/20 h. After the treatment, precipitates on the grain boundary are discontinuous, and the transgranular precipitated phase are mainly GPII zone and η’ phase. The ideal match of grain and grain boundary structure was obtained, and the effective control of strength, conductivity and corrosion resistance is achieved. The properties match of high strength and high conductivity is obtained as required.Compared with the original product, the chemical composition and microstructure the aluminium alloy prepared by trail-production are basically the same. The tensile strength, yield strength, elongation rate, conductivity, thermal conductivity reach 658~665 MPa、620~628 MPa、11.1~12.2%、19.2~19.7 MS/m、146~150 W/(m·K), respectively. The match of strength and conductivity has distinct advantage over the original materials, while the corrosion resistance is equally good. The aluminum alloy rod studied in this research shows apparent superiority. The screws processed with the aluminum alloy prepared in this research have equally good overall performance and some even better properties, thus a successful replacement of the original product is achieved. |
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