Abstract
The effect of low-frequency electromagnetic fields on the micro-structure and macro-segregation of 5A90 alloy ingots during the semi-continuous casting process were quantitatively investigated. The ingots of a 5A90 alloy with a diameter 170 mm were produced by the conventional direct chill casting (DCC) process and low-frequency electromagnetic casting (LFEC) with 10 Hz/100 A. The results showed that LFEC can substantially refine the micro-structure and shorten the width of the columnar grain area of an ingot. The refinement effect came with the relieving of grain boundary segregation and an improvement in the macro-segregation of the ingot. Compared with the traditional DCC process, the tensile properties of the aged alloy prepared by the LFEC process were improved due to the effects of the increase in solid solubility and the strengthening of the grain refinement, so that the stability of the tensile properties was also improved. Meanwhile, the rate of yield increased by 2.3% with a decrease in the peeling thickness of the ingot.
Highlights
Al-Mg-Li alloys have been widely applied in aeronautics and spaceflight due to their outstanding comprehensive performance in terms of their low density, medium strength and high elastic modulus [1,2,3]
With the application of the low-frequency electromagnetic casting (LFEC) process, the micro-structure became smaller grains with a larger size and showed high in-homogeneity with an increase in grain size from the and more uniform, while the refinement effect of LFEC at the center was slightly weaker than that border to the center of the ingot
The main reason for grain refinement during LFEC is the fast cooling effect due to the intensified heat transfer between the liquid refinement during LFEC is the fast cooling effect due to the intensified heat transfer between the and the wall of the mold and at the solidification front resulting from the fast flow that is enforced by liquid and the wall of the mold and at the solidification front resulting from the fast flow that is the Lorentz force [14]
Summary
Al-Mg-Li alloys have been widely applied in aeronautics and spaceflight due to their outstanding comprehensive performance in terms of their low density, medium strength and high elastic modulus [1,2,3]. They are liable to cause some casting defects including coarse grain, severe dendrite structure (micro-segregation) and center line macro-segregation. The macro-segregation of large sized ingots produced by conventional direct chill casting (DCC) processes is serious [4], owing to the broad crystallization temperature interval of the alloy and the unsuitable heat transfer condition at the solidification front during casting [5], which reduces the yield rate of the alloy and causes some adverse effects on its micro-structures and mechanical properties. It becomes rather important to minimize the effects of macro-segregation
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