Research Of 7A04 Aluminum Alloy Semi Solid Slurry Prepared By Short-Time Electromagnetic Stirring And Grain Refiner Addition

This text aimed at 7A04 high strength wrought aluminum alloy, semi-solid slurry of which was prepared by short-time electromagnetic stirring, grain refiner addition and their combined process in large-volume conditions(diameter of slurry maker is about 180mm; slurry mass is more than 5kg every time). This is an exploring job to fulfill large scale and low cost near-net forming of 7A04 aluminum alloy in the industry.The effects law of short-time electromagnetic stirring, grain refiner addition and their combined action on microstructure of 7A04 aluminum alloy large-volume semisolid slurry, distribution of microstructure in the radial direction of crucible, main phases in primary α-Al grain and distribution of main alloy elements were systematically investigated. The results indicate that primary a-Al grains of 7A04 aluminum alloy semi-solid slurry became finer, and average shape factor first increases and then keeping stable with the pouring temperature decreased, stirring power increased and longer stirring time under condition of this paper. The optimized processing parameters were the pouring temperature of 650℃, the nominal stirring power of 3kW and the stirring time of 40s. Microstructure of 7A04 aluminum alloy semisolid slurry is finer and more globular, the inhomogeneity in the radial direction of crucible is restricted significantly under the optimized processing parameters, average equivalent diameter and shape factor of primary α-Al grains of 7A04 aluminum alloy semisolid slurry with SEMS is 81μm and 0.49 respectively and the coefficient of variation Cv is merely 2.1% at 631℃.Microstructure of 7A04 aluminum alloy semisolid slurry is greatly refined and spheroidized by addition of grain refining element Zr and Sc. Average equivalent diameter and shape factor of primary α-Al grains of 7A04ZrSc aluminum alloy semisolid slurry without EMS is 46μm and 0.63 respectively at 631℃, but the homogeneity in the radial direction of crucible has yet to be improved.Microstructure of 7A04 aluminum alloy semisolid slurry is strongly refined and spheroidized, the inhomogeneity in the radial direction of crucible is restricted in the maximum level under the combined action of short-time electromagnetic stirring and grain refiner addition. Average equivalent diameter, shape factor and he coefficient of variation Cv of primary α-Al grains of which is 36μm,0.68 and 0.8% respectively.The result of phase analysis through XRD indicated that the main phases of 7A04 aluminum alloy semisolid slurry prepared by different processes are a-Al, MgZn2 and Al2Cu, the effects of different processes on the phase composition of 7A04 aluminum alloy semisolid slurry are not distinct. The result of EDS analysis indicated that short-time electromagnetic stirring could improve significantly the phenomenon of main alloy elements pile up around the primary α-Al grains for 7A04 aluminum alloy semisolid slurry, reduce the concentration gradient of main alloy elements in the metal liquid around primary a-Al grains, and improve significantly relative intracrystalline solubility in primary α-Al grains of main alloy elements.