Microstructure and fatigue characteristics of direct chill cast and electromagnetic cast 2024 Al alloy ingots
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20/6/03
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Microstructure and Fatigue Characteristics of Direct Chill Cast and Electromagnetic Cast 2024 Al Alloy Ingots SUG WON KIM and HAI HAO The distinct advantages of the electromagnetic casting (EMC) process consist in the presence of stirring motions in the melt, which lead to significant grain size reduction in solidified ingot. Furthermore, surface and subsurface qualities are improved due to the absence of ingot mold. However, it is impossible to achieve the aforementioned advantages in conventional direct chill casting (DCC). In order to contrast the before and after heat treatments of the microstructural and mechanical characteristics of EMC and DCC 2024 aluminium alloys, optical microscopy, scanning electron microscopy, transmission electron microscopy (TEM), X-ray diffractions (XRD), differential scanning calorimetry (DSC), etc. were carried out. Compared with the DCC ingot, the EMC ingot has better mechanical properties not only in the ascast condition but also in the as-aged condition. The DSC curves show that the EMC specimens have high enthalpy, i.e., the thermal kinetic energy to form precipitates during the aging treatment process. Despite heat treatments applied to the DCC ingot, it fails to attain the same mechanical properties as the EMC ingot. Moreover, considering the expensive scalping operation for DCC ingots, the EMC technique, which offers a lower manufacturing cost, is one of the best manufacturing methods used in obtaining the ingots of wrought aluminum alloys.
I. INTRODUCTION Electromagnetic casting (EMC) is a technology developed by combining magnetohydrodynamics and casting engineering. The electromagnetic forces produced by interaction of eddy currents induced in the metal with the magnetic field of the inductor supporting the liquid metal form a stable column. The absence of mold eliminates liquation buildups and feather, and, consequently, the surface finish of the ingot is usually smooth enough to be hot rolled without the scalping operation required following direct chill casting.[1,2] In addition, the significant feature of the EMC method is that the grain size is smaller and the ingot structure is more homogeneous over the entire cross section. The liquation in the circumferential zone of the ingot is negligible. Even though many investigations have been carried out to examine electromagnetic and magnetohydrodynamic phenomena in aluminum EMC, the studies about the characterization of microstructure, mechanical properties, and heat treatment in such caster are comparatively few.[3] This article is an attempt to remedy this deficiency. As a general average, 85 pct of aluminum is used for wrought products. 2024 is also a popular wrought alloy and its ingot is usually cast by the direct chill casting (DCC) method. However, DCC ingots may exhibit a wide spectrum of solidification defects, from cracking, through porosity, to segregation. Hot working can break down the cast structure and achieve uniformity of grain size as well as constituent size and distributio
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