Influence of ultrasonic melt treatment on the formation of primary intermetallics and related grain refinement in aluminum alloys

Abstract

Ultrasonic melt treatment (UST) is known to induce grain refining in aluminum alloys. Previous studies have clearly shown that in Al-Zr-Ti alloys, the primary Al 3 Zr intermetallics were dramatically refined by cavitation-assisted fragmentation, and a good refinement effect was achieved. In this article, Al-Ti, Al-Ti-Zr alloys, and some commercial aluminum alloys are used to analyze the effect of UST on primary intermetallics and grain refinement. The addition of a small amount of Al-3Ti-B master alloy is also studied in order to compare with the addition of Ti and Zr in commercial aluminum alloys. Experimental results show that the ultrasonic grain refining effect is not only related to the size of particles which are refined and/or dispersed by UST, but also related to an undercooling available for activation of these particles in the solidification process. Athermal heterogeneous nucleation theory is considered to explain the effect of size and distribution of substrate particles on the grain structure with different undercoolings. The distribution of primary particle sizes results in the distribution of required undercoolings. Grain refining occurs when the undercooling is large enough to activate the refined primary intermetallics or dispersed inoculants.

A New Al-Zr-Ti Master Alloy for Ultrasonic Grain Refinement of Wrought and Foundry Aluminum Alloys

“…A previous grain refinement study on an Al-2.5 wt.% Cu alloy containing 0.2 wt.% Zr added by a commercial master alloy reported a grain size of 280 lm without ultrasonication; however, ultrasonication at 700°C resulted in significant grain reduction to 58 lm. 9 It can be ascertained from the analysis of previous investigations 7,9,15 and the present study that ultrasonic treatment results in a much greater reduction in grain size of the alloy inoculated with MA1 type master alloy (or Zr and Ti added separately). But with MA2-type master alloy, where a large volume of fine Al 3 Zr particles are already present, a smaller proportion of the grain refining achieved results from ultrasonication.…”

“…5,6 In particular, ultrasonication (US) of molten Al alloys was found to reduce the size and change the morphology of the intermetallics that usually form above the solidification temperature of aluminum. 7 Grain refining in Al alloys containing Zr that has been subjected to US was reported in the 1960s 8 but without proper analysis of the mechanisms. Considerable grain refinement was achieved in Zr and Ti containing pure Al, Al-Cu alloys, and in a number of commercial alloys when ultrasonic cavitation was applied in the temperature range of primary solidification of intermetallics.…”

“…Considerable grain refinement was achieved in Zr and Ti containing pure Al, Al-Cu alloys, and in a number of commercial alloys when ultrasonic cavitation was applied in the temperature range of primary solidification of intermetallics. 7,9 It was suggested that the refinement of large (tens of lm) primary Al 3 Zr intermetallic particles to a size of a few lm and their dispersion make them suitable for becoming heterogeneous nucleation sites for the aluminum. 7,9 It was also found that the Al 3 Zr phase readily nucleates on alumina inclusions.…”

Evolução Do Curso De Engenharia De Minas Na Uemg/João Monlevade Em Seus 10 Anos De Existência

“…de aprimorar a qualidade de metais fundidos por meio de oscilações elásticas (ESKIN, 1995;BEIL, 2015). O funcionamento do tratamento por ultrassom consiste essencialmente na aplicação de ondas acústicas na faixa de frequências de 17 a 20 kHz ao metal fundido, de modo a provocar cavitações e misturar o metal fundido (ZHANG et al, 2011). Essa propagação de ondas ocasiona o fenômeno conhecido como cavitação, ocorrendo o refinamento de grãos através da quebra dos braços dendríticos e nucleando um novo grão (GABATUHULER, 1992;ESKIN, 1998;ABRAMOV, 1994;ZHANG et al, 2011).…”

Correlation vs. Causation: The Effects of Ultrasonic Melt Treatment on Cast Metal Grain Size

“…Zhang et al [16] studied the effects of cooling rate and UST on the microstructures of a variety of aluminum alloys as shown in Table 1. Different cooling rates were achieved by treating the specimens with ultrasound (amplitude of 40 µm, frequency, intensity, horn dimensions and depth were not reported) in a certain temperature range, then pouring the melt in either a graphite mold (0.8 K/s), copper mold (2.0 K/s), through a launder to a steel mold (2.0 K/s), or by direct chill (DC) casting (6.0 K/s).…”