Effects of ultrasonic melt processing on microstructure, mechanical properties and electrical conductivity of hypereutectic Al-Si, Al-Fe and Al-Ni alloys with Zr additions

KMUTT Faculty of Engineering Strong Research Initiative 2020; EPSRC (UK) project UltraMelt2 (EP/R011095/1)

Effect of Cu addition on the microstructure, mechanical and thermal properties of a piston Al-Si alloy

This work was financially supported by The Research and Researchers for Industry (RRi) under the Thailand Research Fund (TRF) that offers a scholarship for Ph.D. student (PHD57I0060) with Thai Metal Aluminium Co., Ltd and King Mongkut’s University of Technology Thonburi through the “KMUTT 55th Anniversary Commemorative Fund”

Structure modification upon ultrasonic processing of an AA4032 piston alloy: comparison of permanent mold and direct-chill casting

© The Author(s) 2019. Piston Al-Si alloys have very complex compositions and multi-phase heterogeneous structure, so it is necessary to control the formation of primary and eutectic compounds. In this study, the ultrasonic melt processing (USP) of a eutectic Al-Si piston alloy (AA4032-type) was performed in a permanent mold and during direct-chill (DC) casting to study its effects on the structure refinement and modification. The principal difference between these two ways of casting is that in the permanent mold the solidification front progressively moves towards the ultrasound source, while in the DC casting the position of the solidification front is fixed in space. The results showed that the USP can successfully refine primary Si, Fe-containing intermetallics and aluminum grains. Refinement of primary Si was accompanied by the increase in its amount, which was attributed to both enhanced heterogeneous nucleation and fragmentation. The refinement of Fe-containing intermetallics and Al grains resulted from the fragmentation mechanism and were more pronounced when USP was applied below the liquidus temperature in the permanent mold. However, the eutectic phases coarsened upon USP, and this effect was most pronounced when USP was applied to the semi-solid material. This was related to the strong attenuation of acoustic waves, which effectively heats the semi-solid material and induces corresponding coarsening of the phases. Acoustic streaming induced by an oscillating sonotrode affected the depth of the sump while simultaneously decreasing the macrosegregation, which reflects the dominant role of the melt flow directed against natural convection. The results demonstrated the importance of the solidification stage at which the USP was applied and the specifics of the USP mechanisms acting at the different stages of solidification.King Mongkut’s University of Technology Thonburi (“KMUTT 55th Anniversary Commemorative Fund” postdoctoral fellowship); EPSRC (UK) Project UltraMelt2 (EP/R011001/1, EP/R011044/1, and EP/R011095/1)

Structure refinement, mechanical properties and feasibility of deformation of hypereutectic Al-Fe-Zr and Al-Ni-Zr alloys subjected to ultrasonic melt processing

© 2020 The Author(s). Hypereutectic Al–Fe and Al–Ni alloys offer a potentially attractive combination of properties, e.g. high-temperature strength and stability, high elastic modulus and low coefficient of thermal expansion. This potential, however, cannot be reached unless the structure of these alloys is refined so that their processing becomes possible. In this study, we for the first time apply ultrasonic melt processing for refining the structure of hypereutectic Al-4% Fe and Al-8% Ni alloys with 0.3 wt% Zr addition. Both primary Al3Fe and Al3Ni particles as well as aluminum/eutectic grains are significantly refined. It is suggested that cavitation-induced fragmentation of primary Al3Zr crystals plays a significant role in the nucleation of intermetallics as well as aluminum. Furthermore, the hardness and tensile properties of the alloys substantially increase after ultrasonic treatment due to the refined structure, which also contributes to the considerably enhanced ductility of the alloys. As a result, the fracture mode changes from brittle fracture to ductile fracture. The increase in ductility makes the alloys suitable for hot deformation, which is demonstrated by lab-scale hot rolling. In addition, precipitation hardening of the alloys can be achieved by high-temperature annealing at 450 °C due to retained Zr in the Al solid solution upon solidification. The results are supported by the analysis of the composition of a supersaturated solid solution of Zr in Al and scanning and transmission electron microscopy that confirms the precipitation of coherent Al3Zr nanoparticles. It is demonstrated that a combination of ultrasonic melt processing and alloying with Zr makes it feasible to develop new class of hypereutectic casting and wrought alloys based on the Al–Fe and Al–Ni systems.King Mongkut’s University of Technology Thonburi (KMUTT 55th Anniversary Commemorative Fund); EPSRC (UK) under project UltraMelt2 (EP/R011001/1, EP/R011044/1 and EP/R011095/1)

Synergetic grain refinement and ZrB2 hardening in in-situ ZrB2/AA4032-type composites by ultrasonic assisted melt treatment

Copyright © 2023 The Author(s). In this work, the effects of ultrasonic treatment on in-situ ZrB2 particle-reinforced AA4032-based composites were studied. The composites were synthesized from Al–K2ZrF6–KBF4 system via an in-situ melt reaction. The phase composition, macrostructure characteristics, hardness and tensile properties of the composites were investigated. The results showed that the addition of in-situ submicron ZrB2 particles into the composites resulted in grain refinement, and the increased hardness and tensile properties. The ultrasonic treatment effectively enhanced the uniformity of in-situ ZrB2 distribution, which further enhanced the structure and mechanical properties of the composites. The mechanisms of the ultrasonic treatment in the improvement of in-situ particle distribution and mechanical properties of the composites were discussed.Research Strengthening Project of the Faculty of Engineering, King Mongkut's University of Technology Thonburi. SC acknowledges the financial support from King Mongkut's Institute of Technology Ladkrabang (2564-02-01-007)

Characterization of the Anodic Film and Corrosion Resistance of an A535 Aluminum Alloy after Intermetallics Removal by Different Etching Time

Copyright © 2022 by the authors. The objective of this study was to improve the corrosion resistance of an A535 alloy by removing intermetallics on the alloy surface by alkaline etching to improve the morphologies and properties of the anodic film that was sealed with different sealants. It was found that alkaline etching for 4 min was suitable for dissolving intermetallic particles and simultaneously providing sufficient roughness for the adhesion of an oxide film to the Al matrix. The effect of alkaline etching revealed that a decrease in the intermetallic fraction from 21% to 16% after etching for 2 and 4 min, respectively, corresponded to the increase in the surface roughness, thickness, and consistency of the anodic film. It was also demonstrated that the surface morphology of the anodic films after stearic acid sealing was more uniform and compact than that after nickel fluoride sealing. The electrochemical polarization curves and salt spray test proved that the alloy etched for 4 min and sealed with stearic acid had better corrosion resistance as compared with the aluminum alloy sealed with nickel fluoride.This work was supported by the Research Strengthening of academic year 2563, the Project of Faculty of Engineering, King Mongkut University of Technology Thonburi year 2020

Precipitation hardening and structure evolution in hypereutectic Al-6 % Fe-Zr alloys subjected to ultrasonic melt processing

Data availability: Data will be made available on request.Supplementary material is available online at: https://www.sciencedirect.com/science/article/pii/S0925838823039166#sec0075 .Copyright © 2023 The Author(s). The objective of this research was to study the influence of Zr concentration and ultrasonic melt processing (USP) on the microstructure and precipitation hardening of a hypereutectic Al-6% Fe alloy. Such alloys have a good potential in high-temperature, wear-resistant, and conducting applications but suffer from coarse structure and low strength/ductility, which prevents their processing. The microstructure of the studied alloys consisted of primary Al13Fe4 intermetallics and (Al)+Al13Fe4 eutectic colonies, which were successfully refined by adding Zr and performing USP. The mechanisms of USP and Zr were confirmed for the Al-6 % Fe alloys with a range of Zr additions. The structure refinement led to improved hardness and tensile properties of the alloys. All studied alloys demonstrated strong precipitation hardening effect with hardness increasing 4–5 times, reaching 170 HV for the alloy with 0.4 % Zr after annealing at 400 ℃ for 20 hrs. The electrical conductivity increased from 25 % IACS in the as-cast alloy to 40% IACS in the annealed Al-6% Fe-0.4 % Zr alloy. The prime novelty of this work is a considerable increase of hardness upon annealing, i.e. more than 100 HV, in the Al-6 % Fe alloy with only minute traces of Zr (<0.01 %). The precipitation phenomena were investigated by transmission electron microscopy. The precipitation of the semi-coherent Al13Fe4 phase with Zr segregated to its surface was observed for the first time. All studied alloys (with minute and larger Zr additions) showed the precipitation of this phase, while the alloys with the larger amount of Zr also demonstrated the precipitation of the metastable L12 Al3Zr phase. Therefore, the properties improvement was attributed to the structure refinement and the formation of Zr-modified Al13Fe4 and Al3Zr precipitates in the microstructure.The authors gratefully acknowledge FE-SEM Center, School of Engineering, King Mongkut’s Institute of Technology Ladkrabang and the financial support under project number KREF046409. D.E. acknowledges the financial support from EPSRC (UK) under the project grant PAAM (EP/W00593X/1). S.C. gratefully acknowledges BCAST (UK) for the use of TEM sample preparation facilities. P.P. and C.L. acknowledge the financial support from Thailand Science Research and Innovation (TSRI), through Fundamental Fund 2023 (Project: Advanced Materials and Manufacturing for Applications in New S-curve Industries) and the Research Strengthening Project (year 2563) by Faculty of Engineering, KMUTT

The improvement of deformability in AA7075 alloy through cryogenic treatment and its correlation with microstructural evolution and FE modelling

Data availability: The data that support the findings of this study are available from the corresponding author upon reasonable request.Cryogenic treatment has high potential for improving the deformation behavior through the recrystallization at a low temperature. In this work, true stress–strain curves were obtained via compression tests to understand the deformation behavior of an AA7075 under cryogenic conditions. Results showed a significant improvement in the flow stress of AA7075, increasing from 260 to 560 MPa at the yield point. The strain hardening exponent (n) also increased from 0.25 to 0.35 after deformation at cryogenic temperatures. The presence of Al2CuMg phase influenced the deformation texture of the tested aluminum alloy, resulting in more elongated grains and fine sub-grains after deformation at cryogenic temperatures, due to the hindered recrystallization. Microstructure evolution after deformation at room and cryogenic temperatures was investigated using EBSD technique to characterize texture and recrystallized grains. The results indicated that the spacing of the high-angle grain boundaries (HAGBs) in the sample deformed at room temperature was slightly larger than in the cryogenically treated sample. The alloy deformed at the cryogenic temperature exhibited a higher strain hardening exponent (n = 0.35) compared to room temperature deformation (n = 0.25). Furthermore, finite element analysis supported the experimental findings, showing that the Plastic Equivalent Strain (PEEQ) of the model tested at cryogenic temperature was higher than at room temperature, attributed to grain refinement during low-temperature deformation. The calculated effective stress responses at cryogenic temperatures for the investigated flow stress aligned well with the experimental results. These new aspects and mechanisms of deformation of aluminum alloys at cryogenic temperatures can improve the formability of high-strength alloys in the future production of more complex and integrated lightweight components.The authors acknowledge the financial support provided by the Office of National Higher Education Science Research and Innovation Policy Council (NXPO), Thailand, through Program Management Unit for Human Resources & Institutional Development, Research and Innovation (PMU-B), Grant No. B05F63098

Constitutive behavior of an AA4032 piston alloy with Cu and Er additions upon high temperature compressive deformation

The Research and Researchers for Industry (RRi); King Mongkut’s University of Technology Thonbur