Effects Of DC Current On Microstructures And Properties Of 6061 Alloy During Homogenization, Solution And Aging Treatments

6061 alloy belongs to heat-hardening aluminum alloy, and has excellent comprehensive properties and abroad applications. In this paper, microstructural observations, EDS analysis, hardness and conductivity tests are used to investigate the effects of DC current on microstructures and properties of 6061 alloy during homogenization, solution and aging treatments.Elevating homogenization temperature and applying DC current can promote the dissolutions of ?-AlFeSi phase and Mg2Si phase and accelerate the transformation from ?-AlFeSi phase to a-AlFeSi phase, and decrease the area fraction of residual phases. When the alloy homogenized at 520?/2h, some coarse needle-like ?-AlFeSi phases (Al5FeSi) become discontinuous and start to transform to ?-AlFeSi phases (Al8Fe2Si) with smaller size. After homogenized at 560?/2h, only a very small amount of second phases exist in the matrix, and most of them are ?-AlFeSi phases, the area fraction of the second phases reduces from 3.003% in cast alloy to 0.647% and 0.356%, respectively, in alloy homogenized without and with DC current. At the same time, Mg2Si phases dissolve completely after homogenized at 560?/2h with DC current.Elevating homogenization temperature and applying DC current can both increase the hardness and decrease the conductivity of the alloy. The hardness of the alloy is the highest, and while the conductivity is the lowest, after homogenized at 560?/2h. The hardness and conductivity of the alloy homogenized at 560?/2h without DC current are 76.55HV and 41.1%IACS, respectively, and are 92.92HV and 40.9%IACS, respectively, of the alloy homogenized at 560?/2h with current.The solution treatment can promote Mg2Si phases to dissolve, and increases the solubility of the alloy elements, and thus increases hardness and decreases conductivity. During aging treatment, the precipitation of strengthening phases and the decrement in solubility can significantly raise the hardness and conductivity of the alloy.With increasing solution temperature, the hardness of aged alloy first increases and then decreases, and while the conductivity shows a decreasing trend all the time. When the solution temperature is 550?, the aged alloy has the highest hardness. The optimum solution temperature is 550?. The hardness and conductivity are 134.28HV and 43.0%IACS, respectively, after the alloy treated at 550?/30min/0A+170?/3h, and are 136.48HV and 43.8%IACS, respectively, after the alloy treated at 550/30min/500A+170?/3h.With prolonging aging time, the hardness of the alloy first increases and then decreases, while the conductivity shows an increasing trend all the time. With increasing aging temperature, the hardening rate is accelerated, and the time to peak hardness is shortened, but the peak hardness decreases, and while the conductivity increases with a higher hardening rate at the early stage. Aging at 170? and 190?, the time to peak hardness are 10h and 7h, respectively. At 150?, the peak hardness can not achieve until 48h. The best aging temperature is 170?. The peak hardness are 145.32HV and 147.25HV after alloy solution treated at 550?/30min without and with DC current and final aged at 170?.Applying DC current during solution is beneficial for the dissolution of Mg2Si, and increases the solubility of the alloy elements and the driving force of aging precipitation, so that increases hardness and decreases conductivity of solution treated alloy, and also increases hardness of ageing alloy. However, the conductivity of ageing alloy shows different behaviors depending on the dual functions of the decomposition of the supersaturated solid solution and the increasing amount of aging precipitates.Applying DC current during aging treatment can inhibit the strengthening phases from precipitating. Compared with aging without current, the alloy aged with DC current has lower hardness, longer time to peak hardness, and lower peak hardness and conductivity. The peak hardness is 140.44HV after alloy solution treated at 550?/30min and then aged at 170?/20h.