Quantitative approach to realization of ultrasonic grain refinement of Al-7Si-2Cu-1Mg alloy

Soo-Bae Kim,Jung-Moo Lee,Min-Su Jo,Young-Kook Lee,Jae-Gil Jung,Young-Hee Cho

doi:10.1038/s41598-019-54161-7

Soo-Bae Kim, Jung-Moo Lee + Show 4 more

Open Access

https://doi.org/10.1038/s41598-019-54161-7

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Abstract

Ultrasonic melt treatment (UST) was applied to Al-7Si-2Cu-1Mg melt at various temperatures of 620, 650, 700 and 785 °C. MgAl2O4 particles which were often found to be densely populated along oxide films, became effectively dispersed and well-wetted by UST. Transmission electron microscopy work combined with crystallography analysis clearly indicates that MgAl2O4 particles can act as α-Al nucleation site with the aid of UST. However, with UST, grain refinement occurred only at temperature of 620 °C and the grain size increased from 97 to 351 μm with increase of melt temperature to 785 °C for UST. In quantitative analysis of grain size and MgAl2O4 particle diameter, it was found that ultrasonic de-agglomeration decreased mean particle size of the MgAl2O4 particles, significantly reducing size from 1.2 to 0.4 μm when temperature increased from 620 to 785 °C. Such a size reduction with increased number of MgAl2O4 particles does not always guarantee grain refinement. Thus, in this work, detailed condition for achieving grain refinement by UST is discussed based on quantitative measurement. Furthermore, we tried to suggest the most valid grain refinement mechanism among the known mechanisms by investigation of the relationship between grain size and particle size with variation of melt temperature.

Highlights

Ultrasonic melt treatment (UST) was applied to Al-7Si-2Cu-1Mg melt at various temperatures of 620, 650, 700 and 785 °C
In order to discuss the effect of number and size of the particles on grain refinement by UST for the alloy, potency of MgAl2O4 for Al nucleation should first be confirmed
MgAl2O4 particles with a faceted morphology were found to be present within α-Al grains (see inset of Fig. 1(a)); a thin foil transmission electron microscope (TEM) sample containing the area of interest was prepared by a JEOL JIB-4601F focused ion beam (FIB)

Summary

Introduction

Ultrasonic melt treatment (UST) was applied to Al-7Si-2Cu-1Mg melt at various temperatures of 620, 650, 700 and 785 °C. Quested et al.[7] and Greer et al.[6] estimated the relationship between TiB2 particle size and α-Al grain size when total volume of TiB2 in the melt is constant In their reports, the number of particles increases as the mean particle diameter decreases and this leads to a decrease in the grain size. In case of inoculation with UST, the ultrasonically induced shock wave and acoustic streaming can de-agglomerate and disperse inoculant particles, increasing the number of nucleation events[10,11]. Even in the absence of inoculants, the increase in local pressure and temperature by UST are suggested to improve the wettability of non-wetting oxide particles, which are naturally present in an Al melt, thereby enhancing the heterogeneous nucleation of α-Al grains[14,16]

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