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Al-8Zn-2Mg-1.5Cu-0.15Sc-0.15Zr alloy with high-strength performance as well as good castability has been developed. In this study, effects of electromagnetic stirring melt treatment (ESMT) on microstructure and mechanical properties of the alloy in the squeeze casting process were investigated. The results show that solidification structure and mechanical properties are significantly improved by ESMT; compared with the conventional squeeze casting, the average grain size decreases from 112 μm without ESMT to 53 μm with ESMT. Meanwhile coarse primary Al3(Sc, Zr) particles unavoidably occurred in cases without ESMT disappear, and segregation degree of the main elements of Zn, Mg, Cu are greatly alleviated; the tensile strength increases from 590 MPa to 610 MPa, and the elongation increases from 9% to 11%. The structure refinement and homogenization should owe to uniform temperature and composition distribution by ESMT under squeeze casting with rapid solidification. [ABSTRACT FROM AUTHOR]

Uniform direct chill (UDC) casting method was developed by combining annular electromagnetic stirring (A-EMS) with intercooling in direct chill casting. In order to investigate effect of UDC on flow patterns, temperature profiles and solidification during the casting, a numerical model of the UDC casting process was developed and used to simulate the UDC casting process for preparing 7005 aluminum alloy billets. The comparison of the calculated results of UDC casting with normal direct chill (NDC) casting indicated that flow patterns, temperature profiles and the sump depth are modified remarkably by the application of annular electromagnetic stirring and intercooling during the direct chill casting. The sump profile and the temperature history during UDC casing were studied, and the mechanism of the casting process were discussed. The comparisons between the simulations and experimental results suggested that the proposed model provides good agreement for the sump profiles and the temperature history within the billets. fx1 [ABSTRACT FROM AUTHOR]

By coupling annular electromagnetic stirring with intercooling, a uniform direct chill (UDC) casting process has been developed to achieve fine and uniform microstructure for the large-sized aluminium alloy billets. In this study, the solidification behaviour of Φ508 mm 7005 alloy during UDC casting process was investigated, and the effect of the processing parameters on the microstructures and segregation of the billets were examined. The results indicated that, the solidification structure could be remarkably refined in the UDC casting process, and subsurface segregation could be alleviated by adjusting the vertical position of the stirring coils. [ABSTRACT FROM AUTHOR]

In this study, large-sized Al–Zn–Mg–Cu alloy billets were prepared by direct chill casting imposed with annular electromagnetic stirring and intercooling; a process named uniform direct chill casting. The effects of uniform direct chill casting on grain size and the alloying element distribution of the billets were investigated and compared with those of the normal direct chill casting method. The results show that the microstructures were refined and the homogeneity of the alloying elements distribution was greatly improved by imposing the annular electromagnetic stirring and intercooling. In uniform direct chill casting, explosive nucleation can be triggered, originating from the mold wall and dendrite fragments for grain refinement. The effects of electromagnetic stirring on macrosegregation are discussed with consideration of the centrifugal force that drives the movement of melt from the central part towards the upper-periphery part, which could suppress the macrosegregation of alloying elements. The refined grain can reduce the permeability of the melt in the mushy zone that can restrain macrosegregation. [ABSTRACT FROM AUTHOR]

There are two critical stages of grain refinement during solidification: above and below the liquidus temperature. The key to improve the refinement potential is ensuring the nucleation sites precipitate in large quantities and dispersed in the melt above liquidus. In this work, internal cooling with annular electromagnetic stirring was applied to an Al-Zn-Mg-Cu-Zr alloy at a temperature above liquidus. A systematic experimental study on the grain refining potential was performed by combining different melt treatments and pouring temperatures. The results indicate that internal cooling with annular electromagnetic stirring (IC-AEMS) had a significantly superior grain refining potency for the alloy compared to traditional electromagnetic stirring (EMS). In addition, homogeneous and refined grains were achieved at high pouring temperatures with IC-AEMS. The possible mechanisms for the enhanced grain refinement above the liquidus temperature are explained as the stable chilling layer around the cooling rod in IC-AEMS providing undercooling for the precipitation of Al3Zr nucleant particles and the high cooling rate restraining the growth rate of these particles. At the same time, forced convection promotes a more homogeneous distribution of nucleant particles. [ABSTRACT FROM AUTHOR]

This study presents a modified annular electromagnetic stirring (M-AEMS) melt treatment suitable for a large-volume and high-alloyed aluminum alloy. A 3D computational model coupling an electromagnetic model with a macroscopic heat and fluid-flow model was established by using Ansoft Maxwell 3D and Fluent from ANSYS workbench, and the effects of the electromagnetic shielding ring, the height of the magnet yoke, the shape of the iron core, and the internal cooling mandrel on the electromagnetic, thermal and flow fields were studied numerically. Based on the optimal technical parameters, the effectivity of the M-AEMS process by using 7075 alloy was validated experimentally. The results show that a favorable electromagnetic field distribution can be achieved by changing the magnet yoke height, the iron-core shape and the electromagnetic shielding ring, and the melt temperature of the 7075 alloy can drop rapidly to the pouring temperature by imposing the internal cooling mandrel; compared with ordinary annular electromagnetic stirring, the M-AEMS process creates a lower magnetic strength near the melt top, beneficial for stabilizing the melt surface; meanwhile, it yields a higher magnetic strength near the melt bottom, which increases the shear rate and ensures an optimal stirring effect. Therefore, M-AEMS works more efficiently because the thermal and composition fields become uniform in a shorter time, which reduces the average grain size and the composition segregation, and a more stable melt surface can be obtained during treatment, which reduces the number of air and oxide inclusions in the melt. [ABSTRACT FROM AUTHOR]

The nucleation and grain growth that occur during solidification have been extensively examined, but insight into the influence of an external field on the formation of heterogeneous crystal nuclei above the liquidus remains unclear in the peritectic refinement mechanism. In this work, we studied the effect of cooling rate above the liquidus on the formation of primary Al3Zr and grain refinement in Al-0.2%Zr alloys with inter-cooling annular electromagnetic stirring (IC-AEMS). The results show that the size and distribution of primary Al3Zr are greatly improved, and the morphology transformed from large plate/blocky shapes without IC-AEMS to small blocks with IC-AEMS. Meanwhile, above the liquidus, the addition of an Al-Zr master alloy to pure Al alone did little to enhance the refinement, but after IC-AEMS, the grains were refined dramatically. The refinement result seems to be explained by two hypotheses of pre-nucleation and explosive nucleation. [ABSTRACT FROM AUTHOR]