Research On Preparation Of The Large-Volume Semi-Solid Slurry Of Wrought Aluminum Alloy By Electromagnetic Stirring

Due to its high strength and good plasticity, high strength wrought aluminum alloy is widely used as components material of aircraft and high-speed train. Combining the advantages of the traditional casting and plastic forming, semi-solid forming technology is a suitable way to form wrought aluminum alloy due to its low cost and near net shaping characteristics. But the present study mainly focuses on thixoforming and preparing small-volume slurry, so it is necessary to quantitatively research the disposable large-volume (more than5kg) rheological slurry preparation of7A04aluminum alloy and its rules.The effect of the Electromagnetic Stirring (EMS) process parameters on microstructure of large-volume (diameter of slurry maker:Φ180mm; more than5kg every time) semi-solid slurry of7A04aluminum alloy was studied with temperature-controllable electromagnetic stirrer. The results show that, under the experimental condition in this paper, the primary a-Al particles of the semi-solid slurry are finer at higher voltage and slurry temperature, namely the overall quality of the semi-solid slurry is the best at EMS voltage of230V, slurry temperature of638℃and EMS frequency of5Hz, with average equivalent diameter of112μm.Aiming at the radial inhomogeneous phenomenon of large-volume semi-solid slurry prepared by EMS process, the effect of EMS voltage and frequency on its radial homogeneity was studied in this paper. Then, the equipment was improved to be annulus electromagnetic stirrer to study the homogeneity differences of semi-solid slurry under different stirring gap width. The results show that, under the experimental condition in this paper, the slurry microstructure at1/2radius location of the slurry maker is better than that at the center and the edge; improved annulus electromagnetic stirrer can improve the radial homogeneity of semi-solid primary phase; proper stirring gap width can get better comprehensive effect of quality and radial homogeneity of semi-solid7A04aluminum alloy slurry.The corrosion performance of the sample of semi-solid microstructure by EMS was studied through the salt spray test and polarization test, and compared with dendritic crystal sample. The results show that, in neutral salt spray test, corrosion weightless rates of the sample of semi-solid microstructure is higher than dendritic crystal sample in the early stage, but lower in the later stage. Both average corrosion depth and maximum corrosion depth of the corrosion pits of dendritic crystal sample are greater than the sample of semi-solid microstructure. In the polarization test, corrosion of the sample of semi-solid microstructure is lighter. According to polarization curve, corrosion potential of sample of semi-solid microstructure is higher than dendritic crystal sample, namely corrosion performance of the former is better. The main cause is that pitting corrosion causing by the Cl-and intermetallic compounds of aluminum oxide film expands faster in the grain boundary of dendritic crystal sample.