The Effect of Ultrasonic Melt Treatment on Macro-Segregation and Peritectic Transformation in an Al-19Si-4Fe Alloy

Abstract

It is well documented that ultrasonic melt treatment (USMT) can refine dendritic and eutectic microstructures during solidification, but much less attention has been paid to the effect of USMT on macro-segregation and intermetallic transformations. In this research, macrosegregation and primary Fe-containing intermetallic peritectic transformations in an Al-19 wt pct Si-4 wt pct Fe alloy were investigated without and with USMT. Macrostructural examination showed that in the absence of USMT the ingot revealed considerable nonuniform distribution of both the primary Fe-containing intermetallic and primary Si particles, whereas the ingot with USMT exhibited near homogeneous distribution of both primary phases, i.e., reduced macro-segregation. The beneficial effect of USMT on relieving macrosegregation was further examined using quantitative microstructural metallography and the results indicated that the area fraction, number density, and size distribution of both primary phases became essentially uniform across the ingot after USMT. USMT further exerted a significant impact on the constitution of the primary Fe-containing intermetallics, where complex particles of δ-Al3FeSi2/β-Al5FeSi were prominent without USMT while few δ-Al3FeSi2 particles were observed after USMT and the primary Fe-containing intermetallics existed mostly as the single-phase β-Al5FeSi. The underlying reason was attributed to the

Structure Modification upon Ultrasonic Processing of an AA4032 Piston Alloy: Comparison of Permanent Mold and Direct-Chill Casting

“…These particles are formed as primary phases in the range of temperatures from 873 K to 888 K (600°C to 615°C) to 853 K (580°C) either directly for the melt or as a product of peritectic reaction with the d (AlFeSi) phase [26,27] and, hence, are subjected to the same refinement mechanisms as primary Si. These results agree well with the reported refinement of the b-Al 5 FeSi particles upon USP performed in the temperature range 983 K to 958 K (710°C to 685°C), [19] 973 K to 883 K (700°C to 610°C) [14] , or 973 K to 873 K (700°C to 600°C…”

“…In addition, the acoustic streaming was shown to distribute primary intermetallics more uniformly in the treated volume. [14] Grain refinement upon USP has been demonstrated on a number of Al-based hypo-eutectic alloys. [11,15] For near-eutectic Al-Si alloys, the refinement of primary Si and some intermetallics have been reported.…”

3D characterization of ultrasonic melt processing on the microstructural refinement of Al Cu alloys using synchrotron X-ray tomography

“…Gas pores usually exhibits round shape. this phenomenon also can be found in Refs [8][9][10][11][12]41]. The enlarged 3D morphology of shrinkage and gas pores are clearly observed in Fig.…”

Ultrasonic Processing for Structure Refinement: An Overview of Mechanisms and Application of the Interdependence Theory

“…It has been reported that the narrow size distribution of refiner particles after UST of Zr added to Mg [6] and Al-Ti-B [67], Al-Zr, Al-Zr-Ti [63] added to Al alloys results in better grain refinement. The refinement of blocky and needle shape primary intermetallic phases such as Al 3 Ti [63,68], Al 3 (Zr, Ti) [63,69], primary Si [70,71,72] and β/δ-Al-Fe-Si [24,25] phases is an added advantage of UST that further improves the mechanical properties of the cast alloys. Figure 7 shows a summary of the common intermetallic phases encountered in commercial Al alloys and their refinement after UST.…”

“…Liquid and semi-solid melt processing with power ultrasound has received considerable attention and has been successfully demonstrated for the refinement of as-cast grain structure in light alloys without the need for grain refiners, therefore eliminating the limitations associated with inoculation processes for Al and Mg based alloys [20,21,22]. The benefits of ultrasonic treatment (UST) include the production of non-dendritic structures, degasification and the refinement of primary phases (Al 3 Zr, Al 3 Ti, Al-Fe-Si and primary Si) [23,24,25]. This technique has attracted commercial interest due to being environmentally friendly, cost effective and possesses several technical advantages over conventional methods in molten metal processing [23,26,27].…”