Enhanced Refinement of Al-Zn-Mg-Cu-Zr Alloy via Internal Cooling with Annular Electromagnetic Stirring above the Liquidus Temperature

Abstract

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.

Effect of Cooling Rates on the Microstructure and Mechanical Property of La Modified Al7SiMg Alloys Processed by Gravity Die Casting and Semi-Solid Die Casting

“…Figure 14 is the schematics showing the microstructural evolution of La modified Al7SiMg alloys in two casting processes. In gravity die casting (Figure 14a,b), due to the increase of cooling rate (0.2 to 9 K/s), a larger undercooling is achieved and the process of nucleation in the melt is promoted [19,20], the grain size and DAS of α-Al phase are both refined. In addition, under 0.4 wt.% La additions, the Si modification effect of La is enhanced with increasing cooling rate.…”

Research on Microstructure and Mechanical Properties of Rheological Die Forging Parts of Al-6.54Zn-2.40Cu-2.35Mg-0.10Zr(-Sc) Alloy

“…Research [20] shows that in the process of melt cooling, the crucible wall with a lower temperature provides undercooling for the nucleation of Al 3 (Sc, Zr) particles, and electromagnetic stirring makes the temperature field composition field more uniform, which can increase Al 3 (Sc, Zr) particle stability. Research [32] shows that IC-AEMS has both the advantages of rapid cooling and uniform temperature field and composition field, and the role of the inter-cooling rod is similar to the crucible wall, which can provide the melt with more undercooling required for Al 3 Zr nucleation, and IC-AEMS can inhibit the growth rate of Al 3 Zr particles. Therefore, for the Sc-containing 7050 alloy in this paper, IC-AEMS can form more Al 3 (Sc, Zr) nucleating particles, and further refine the grains.…”

Effects of ESMT on Microstructure and Mechanical Properties of Al-8Zn-2Mg-1.5Cu-0.15Sc-0.15Zr Cast Alloy in Squeeze Casting Process

“…On one hand, casting defects in the small-sized squeeze castings can be reduced to some degree for some wrought Al-Zn-Mg-Cu alloys, but there are still unavoidable defects such as shrinkage porosity, and coarse structure in the large-sized squeeze castings, which seriously affect casting performance and mechanical properties [10,11]. In response to this problem, an advanced electromagnetic stirring melt treatment (ESMT) method was developed [12,13], and uniform, fine solidification structure of wrought 7XXX series alloys was obtained by applying electromagnetic stirring in the solidification process [14][15][16]. On the other hand, an ultra-high-strength cast aluminum alloy for squeeze casting, designed by main element composition optimization and Sc and Zr micro-alloying, exhibited good casting properties while maintaining mechanical properties with high strength and high toughness [17].…”