Research Of Preparing Semi-Solid Slurry By Annulus Electromagnetic Stirring And Rheo-Diecasting Of 7A04 Aluminum Alloy

Wrought aluminum alloys are widely used in production and living because of its high strength, good ductility and excellent corrosion resistance. Some excellent mechanical properties and complex components can be formed by rheoforming. In this paper, the slurry preparation, die-casting forming and heat treatment of rheo-diecasting forming of 7A04 aluminum alloys have been studied, which has a certain reference value for industrial production of wrought aluminum alloy rheoforming.In this paper the traditional electromagnetic stirring furnace had been changed into annulus electromagnetic stirring furnace through simple renovation. The high quality semi-solid slurry of 7A04 aluminum alloy was prepared through continuous cooling and continuous stirring. The effects of stirring time and stirring frequency on semi-solid slurry of 7A04 aluminum alloy were systematically studied. The results indicate that the cooling speed of 7A04 aluminum alloy semi-solid slurry increased firstly, then decreased after a peak, finally reached a steady value with the stirring time increasing. As the extension of stirring time, the average shape factor of the 7A04 aluminum alloy semi-solid slurry increased at the beginning, and then decreased, at the end continues enlarged. The changing of average equivalent diameter showed the same rule as the average shape factor. The formation of the semi-solid non dendritic structure was divided into three stages:① the dynamic balance of dendrite shape primary a-Al particle generation and stirring breaking dendrite shape primary a-Al particle, ②a large amount of fine dendrite shape primary a-Al particles outbreak nucleated, ③breaking and growth of dendrite shape primary a-Al particle. Under different stirring frequency, the quality of slurry was similar during 0min-3min of stirrings. The best quality of slurry was found at 5Hz during 3min-6min of stirrings, with average equivalent diameter of 40.46μm and average shape factor of 0.48. During 6min-9min of stirrings, the stirring had the best quality was found at 25Hz, whose average equivalent diameter is 80.66μm and average shape factor is 0.56.In die-casting forming stage, injection velocity measuring device was developed by our-self, The injection velocity of die-casting forming has been measured with real-time and accurately. the filling head’s movement rule of die-casting forming process had been described distinctly and the effect of injection velocity on the micro-structure and mechanical properties of rheo-diecasting of 7A04 aluminum alloy had been studied. The results show that, with the increase of injection velocity, the average equivalent diameter of primary α-Al(α1) and secondary solidified α-Al(α3) of rheo-diecasting have decreased. On the other hand, the average shape factor has increased. The density, hardness and tensile strength of the rheo-diecasting have increased firstly and then decreased as the injection velocity increasing from 0.35m/s to 0.63m/s. When injection velocity was very fast, the rheo-diecasting gas volume increased and the performance of rheo-diecasting decreased. When injection velocity was very slow, the average equivalent diameter of primary α-Al(α1) and secondary solidified α-Al(α3) of rheo-diecasting increased, but the performance of rheo-diecasting decreased. Therefore, a appropriate injection velocity need to be selected in rheo-diecasting process. In this paper,0.58m/s was seletced as best injection velocity.In this paper, there heat treatments were used for 7A04 aluminum alloy, aging only(120℃/24h), tradition solution and aging(470℃/1h+120℃/24h), intensify solution and aging(455℃/2h+480℃/1h+120℃/24h) respectively. The effect of heat treatment on micro-structure and mechanical properties of rheo-diecasting of 7A04 aluminum alloy was studied. The results show that the performance of rheo-diecasting of 7A04 aluminum alloy has been significantly improved through intensify solution and aging(455℃/2h+480℃/1h+120℃/24h). In this paper, the hardness, tensile strength and break elongation of the rheo-diecasting of 7A04 aluminum alloy has improved 67.3%,154.5% and 67.3% respectively based on the die-casting state.