Ultrasonic Melt Treatment Research Articles

Evolution of Al2Cu Secondary Phase and Precipitation Strengthening of 2219 Al Alloy with Ultrasonic Melt Treatment, Hot Rolling, and Solution Aging

This study aims to clarify the combined effect of ultrasonic melt treatment (UST), hot rolling and solution aging (HRSA) on the evolution of the Al2Cu secondary phase in 2219 Al alloy toward the optimization of its mechanical properties for high‐performance structural applications. The results show that UST is beneficial for modifying the morphology and reducing the size of the secondary phase (by an average of 17.9%), and conducive to increasing the Cu content in the Al matrix (by an average of 37.5%) during solidification. The genetic effects of UST on the microstructure generated during HRSA result in denser and finer θ′/θ″ Al2Cu particles precipitating in the α‐Al matrix, with a 62.1% increase in the precipitates volume in the HRSA sample. Theoretical calculations confirm that precipitation strengthening is the predominant mechanism for strength improvement of 2219 Al alloy after UST and HRSA. The ultimate tensile strength (UTS), yield strength (YS), and elongation (EL) of the HRSA alloy without UST are 329, 214 MPa, and 11.9%, respectively, while these parameters are increased by 12.5% (to 370 MPa), 9.8% (to 235 MPa), and 17.6% (to 14.0%) for the UST alloy, respectively.

Microstructure refinement, mechanical performances and degradability of biomedical Zn-2Cu alloy by ultrasonic melting and homogenization treatment

Zn alloys are deemed to be desired body implant materials because of their moderate degradation rate. In this paper, the microstructural evolution, mechanical performances, and degradability of Zn-2Cu alloy prepared by ultrasonic melt treatment (UMT) with different ultrasonic powers (0 W, 300 W, 600 W, and 900 W) were systematically studied. Under the condition of UMT, the coarse α-Zn grains of Zn-2Cu alloy were refined into fine equiaxed grains and the mean size was significantly decreased from 133.4 μm to 65.3 μm when the ultrasound power was enhanced. The precipitating CuZn5 phase was significantly refined from the coarse block into the spherical shape. Moreover, the fraction of the CuZn5 precipitates of the Zn-2Cu alloy was greatly reduced with the increase of ultrasonic power. Tensile tests showed that the ultimate tensile strength (UTS), yield strength (YS), and elongation (El) of Zn-2Cu alloy were remarkably enhanced to 203 MPa, 167 MPa, and 8.14 %, respectively, when the Zn-2Cu alloy melting was treated by 600 W power. It was found by electrochemical polarization test that the degradation rate of Zn-2Cu alloy treated by UMT with 0 W, 300 W, 600 W, and 900 W power in Hank’s solution was gradually decreased to 1.6312 mm/a, 1.3206 mm/a, 1.0992 mm/a, and 1.2832 mm/a, respectively. In addition, after the Zn-2Cu alloys were immersed in Hank’s solution for 30 days, the degradation rate of samples was summarized as 0 W alloy (0.472 mm/a) > 300 W alloy (0.436 mm/a) > 900 W alloy (0.412 mm/a) > 600 W alloy (0.398 mm/a). The studies verified that the UMT was a very valuable technology for preparing Zn-2Cu alloy, which can meet the requirement of mechanical properties and degradable rate as a promising implant material.

Study on the effect of ultrasonic treatment for fabricating nodular cast iron with improved mechanical properties

In this paper, a novel ultrasonic treatment technique was proposed in nodular cast iron melt with the aim of improving the microstructure and mechanical properties of nodular cast iron. The effects of ultrasound on the microstructures and properties were investigated by comparing experiments with and without ultrasound. The results showed that compared with the NO UT specimen, the mean equivalent diameter of graphite nodules was reduced by 46% in the UT 105 s specimen, while the mean roundness and nodule count per unit area were increased by 33.9% and 43.6%, respectively. In addition, the ultrasonic treatment of melt could increase the pearlite content, refine the matrix microstructure and reduce the pearlite interlamellar spacing from 392.7 nm to 231.3 nm. Compared with the NO UT specimen, the mechanical properties of the UT specimen were improved significantly, and could up to UTS of 739 MPa, YS of 579 MPa and El of 9.4% in the UT 105 s specimen. In this work, the mechanism of ultrasonic action on nodular cast iron also was discussed in detail.

Microstructure-strengthening correlation of 2219 Al alloy subjected to ultrasonic melt treatment, hot rolling and heat treatment

Improving strength while retaining good ductility is crucial for expanding the application of 2219 Al alloy. In this study, refined microstructure, excellent strength and ductility were obtained for the 2219 Al alloy under the combined effects of ultrasonic melt treatment (UMT), hot rolling and T6 heat treatment (HRT6). The mean grain size declined from 664.2 μm to 194.9 μm for the as-cast 2219 Al alloy after 240s UMT, with a refining efficiency of 70.7 %. Meanwhile, the Cu content in Al matrix was increased by 41.7 %, and the area fraction of reticular eutectic structure was accordingly lessened by 64.5 %. The nucleation of θʹʹ/θʹ-Al2Cu phase was actuated owing to the increased Cu content in Al matrix, resulting in more dispersive θʹʹ/θʹ-Al2Cu precipitates in the HRT6 alloy with UMT. Besides, the recrystallization was encouraged because the boundaries of refined as-cast grains provided more favorable nucleation sites, and the increased dispersive θʹʹ/θʹ-Al2Cu precipitates would inhibits the grain boundary merging during HRT6. Thus, the average dimension of the recrystallized grains was decreased to the lowest value of 71.3 μm in the HRT6 alloy with 240s UMT. Meanwhile, the ultimate tensile strength (UTS), yield strength (YS) and elongation (EL) were enhanced to 456.2 MPa, 307.0 MPa and 16.7 %, and precipitation strengthening contributed the most to the YS enhancement. The improved ductility was mainly due to the increased deformation capacity induced by the refined grains and reduced stress concentration caused by the dispersive θʹʹ/θʹ-Al2Cu particles.

Investigation of the effect of ultrasonic treatment during crystallization on the structure and properties of deformable aluminum alloys

The article presents the methodology and results of the study of the effect of ultrasonic treatment of the melt of deformable aluminum alloys during crystallization on the structure and properties of the formed ingots: the dependence of the grain score, porosity, size and distribution of inclusions of intermetallides on the amplitude of ultrasound radiation and the frequency of vibrations, as well as the distance to the waveguide. In addition, data on the analysis of the transformation of iron‑containing phases (α‑AlFeSi and β‑AlFeSi) under the action of ultrasound and dissolution of titanium waveguides during ultrasonic treatment of aluminum melt are presented.

Distribution pattern of acoustic and streaming field during multi-source ultrasonic melt treatment process

Distribution pattern of acoustic and streaming field during multi-source ultrasonic melt treatment process

Simultaneously Improved Bendability and Strength of Al–Mg–Si–Cu–Zn Alloys by Controlling the Formation and Evolution of Primary Fe‐Rich Phase

In present work, the formation, evolution, and distribution of the primary Fe‐rich phase in an Al–Mg–Si–Cu–Zn–Fe–Mn alloy are coupling controlled by ultrasonic melt treatment (USMT) and thermomechanical processing (TMP). It is shown in the results that the size of grains and Fe‐rich phase in the as‐cast state can be greatly reduced by the applied optimum USMT at 680 °C. Additionally, the transformation rate of β‐Fe‐rich phase to α‐Fe‐rich phase can be also enhanced. After the coupling control of USMT and TMP, the number density and distribution uniformity of multiscale Fe‐rich particles can be greatly increased or improved, which contributes to the fine‐grained recrystallization microstructure and weakened texture. Finally, compared with the 6xxx series Al alloys (such as AA6016 and AA6111), the alloy sheet in the pre‐aging state exhibits substantially improved bendability and strength (the plastic strain ratio and tensile strength are 0.67 and 304 MPa, respectively). The effect of USMT on the formation and transformation of primary Fe‐rich phase and the mechanisms of improved bendability and strength are deeply discussed.

The microstructure and mechanical properties of 2219 alloy during ultrasonic treatment

High-intensity ultrasonic melt treatment technique plays a key role in improving the performance of large-scale 2219 alloy ingot (Φ630 mm × 4500 mm). In this current paper, ultrasonic treatment-assisted casting techniques were developed and applied to manufacture large-scale 2219 aluminium (Al) alloy ingot in direct chill casting (DC). The industry-level experiments revealed that the α-Al grains of the ingot with ultrasonic (USDC) were refined, the area fraction of the coarse Al2Cu eutectic phase showed a decreasing trend, and the mechanical properties were lightly improved than without ultrasonic ingot (DC). Based on the present results and previous proposed hypotheses, the synergistic effects of cavitation and acoustic streaming were considered as the dominant mechanisms of USDC.

Ultra-fine Nbss/Nb5Si3 in situ composites with remarkable properties prepared by ultrasonic melt treatment

In order to refine coarse silicide and improve mechanical performance of ternary Nb-20Si-5Mo alloy, ultrasonic vibration treatment for ultra-high temperature melt is successfully applied. The results show that the vibration can improve the fluidity and reduce the shrinkage defects. The hypereutectic microstructure transforms into the fine rod-like eutectic. Due to the solute redistribution in ultrasound field, the Mo-rich layer at Nbss and β-Nb5Si3 phase boundary and the semi-coherent relation can be observed. Mo tends to dissolve in Nbss the matrix phase and inhibit the peritectic reaction. The average size of primary silicide is refined from 49.1 to 2.2 µm with 95.52% refinement efficiency, the compressive strength and fracture toughness of 100 s ultrasonic treated specimen improved 6.84% and 50.75% compared with the as-cast specimen, respectively. The heightened constitutional supercooling and the accelerated nucleation caused by cavitation effect are the main reasons of grain refinement.

Adding Value to Secondary Aluminum Casting Alloys: A Review on Trends and Achievements.

Aluminum is a critical element of the circular economy as it can be recycled several times. Moreover, Al recycling is a more economically and environmentally efficient procedure than the primary Al production from ores. Secondary aluminum alloys are mostly used in casting applications since it is possible to accommodate their chemical composition through secondary manufacturing processes. However, the quality of the alloys may be considerably altered during the different steps of the recycling process. Inadequate waste sorting might result in excessive contamination. Iron is the most dangerous contaminant because it causes brittle and fragile intermetallic phases, which significantly impacts the mechanical characteristics of alloys. In addition, the microstructure of the alloy changes significantly after multiple cycles of remelting. These issues lead to the downcycling of aluminum, i.e., in other words, the reduction in the overall quality of the alloys. Thus, it has been shown that a number of procedures, including ultrasonic melt treatment and microalloying with rare earths, can somewhat alter the shape of the Fe-rich phases in order to reduce the shortcomings of downcycling. However, a solid mechanical characterization is still missing in order to improve the Fe-rich phase alteration.

Casting and Characterization of A319 Aluminum Alloy Reinforced with Graphene Using Hybrid Semi-Solid Stirring and Ultrasonic Processing.

Advanced metallurgical processing techniques are required to produce aluminum matrix composites due to the tendency of the reinforcement particles to agglomerate. In this study, graphene nano-platelet reinforcement particles were effectively incorporated into an automotive A319 aluminum alloy matrix using a liquid metallurgical route. Due to its low density, it is a highly difficult task to produce an aluminum matrix composite reinforced with graphene. Hence, this study explored a novel approach to prevent particle floating to the melt surface and agglomeration. This was achieved via a hybrid semi-solid stirring of A319, followed by ultrasonic treatment of the liquid melt using a sonication probe. The microstructure and graphene particles were characterized using optical microscopy and scanning electron microscopy. Furthermore, the interfacial products produced with the incorporation of graphene in liquid aluminum were analyzed with X-ray diffraction. The tensile test results exhibited 10, 11 and 32% improvements in ultimate tensile strength, yield strength, and ductility of A319 reinforced with 0.05 wt.% addition of graphene. Analysis of strengthening models demonstrated primary contribution from Hall-Petch followed by CTE mismatch and load bearing mechanism. The results from this research enable the potential for using cost-effective, efficient and simple liquid metallurgy methods to produce aluminum reinforced graphene composites with improved mechanical properties.

Optimization of Thermo-Mechanical Fatigue Life for Eutectic Al–Si Alloy by the Ultrasonic Melt Treatment

The eutectic cast Al–Si alloys with excellent high-temperature and casting performance are widely used in engine pistons. During frequent starts and stops, the thermo-mechanical fatigue (TMF) is the most important failure cause. Ultrasonic melt treatment (UT) was chosen to compare and investigate the influence of micro-structures on fatigue life and damage mechanisms of as-cast (AC) eutectic Al–Si alloys under TMF loading. After UT, the grain size, primary Si, and intermetallic particles are reduced significantly in the alloy; fatigue life increases obviously. As a result of pilling-up of dislocations, the competitive effects of the critical strain/stress for fatigue crack nucleation can be found. There are two different crack initiation mechanisms under TMF: one is primary Si fracture for AC alloys with limited critical strain/stress for fatigue crack nucleation at fractured Si particles, and the other is primary Si debonding for UT alloys with increasing critical fracture strain/stress. After the crack initiation, the fractured or debonded primary phases provide the advantages for the further development of main cracks for both alloys. The UT alloy (805 ± 253 cycles) has about twice the TMF life of the AC alloy (403 ± 98 cycles). The refinement of micro-structures is instrumental in improving the fatigue resistance and life of TMF for the UT alloy.

The grain refinement of Mg alloy subjected to dual-frequency ultrasonic melt treatment: A physical and numerical simulation

Ultrasonic melt processing of magnesium (Mg) alloys has received widespread attention. However, the cavitation behavior and microstructure evolution are difficult to be directly observed in high temperature melts. In this work, single-frequency ultrasonic field (SUF) and dual-frequency ultrasonic field (DUF) were introduced into succinonitrile (SCN) melt and real-time images of dendrite growth and evolution were captured to explore the regulation mechanism of DUF on melt solidification structure. Numerical simulation and corresponding experiments were performed to investigate the acoustic pressure distribution and cavitation area of DUF in Mg alloy melt. Ultrasonic treatment increased the SCN dendrite growth rate and refined the solidification microstructure, and a higher efficiency was achieved by DUF when compared to SUF when the total electric power was the same. DUF decreased sound pressure attenuation and enlarged cavitation area. A result of this improvement was that its grain refinement efficiency was 13.8% and 25.6% higher than SUF at 15 kHz and 20 kHz, respectively. The input power ratio plays a crucial part in improving the grain refinement efficiency of DUF. While ensuring the symmetrical distribution of cavitation area, the grain refinement efficiency can be significantly optimized by appropriately increasing the power share of 15 kHz ultrasound is optimal at a power ratio of 2:1.

Microstructural Refinement of As-Cast Al–Mg Alloy by Ultrasonic Melt Treatment Using a Titanium Sonotrode under Fully Liquid Condition

The effects of ultrasonic treatment (UST) using a titanium (Ti) sonotrode in a fully liquid stage on the grain refinement and mechanical properties of as-cast Al–Mg alloy billets were investigated. To clarify the grain refinement mechanism, the grain size (GS) and dendrite arm spacing (DAS) were examined as functions of the growth restriction factor (Q) dependent on the Ti dissolution from the sonotrode, and compared to those in the as-cast and re-melted states of the samples inoculated using an Al–10 mass%Ti master alloy. In addition, the formation and dissolution behavior of Al3Ti intermetallic particles acting as a heterogeneous nuclei was indirectly observed by measuring the electrical resistivity during isochronal annealing. In comparison with the chemical refiner inoculation, the UST effectively refined not only the GS but also the DAS, both of which showed similar slightly concave upward curves with an increasing slope against 1/Q. Electrical resistivity measurement results provided indirect evidence that the dissolved Ti was present as a solute during the solidification stage. The GS, DAS, and electrical resistivity results all suggest that the dissolved Ti refined the GS primarily by solute-induced growth restriction effect rather than by providing heterogeneous nucleation sites. The UST effect on the microstructure refinement was efficient when the Ti-dissolution content was as low as less than 0.05 mass%. The refinement of grains, Al3Fe particles, dendrites, and pores by the UST significantly improved mechanical properties, especially the elongation at break.

A Study on the Interrelationship between the Microstructural Features and the Elevated Temperature Strength of Multicomponent Al-Si-Cu-Ni Casting Alloys

The elevated temperature strength of multicomponent Al-Si alloys is greatly affected by the volume fraction and the interconnectivity of hard phases formed upon solidification. In the present investigation, such influences were examined for two Al-Si-Cu-Ni alloys with different total volume fractions of hard phases. To control the microstructural features related to the size of the phase, the specimens were prepared with and without ultrasonic melt treatment (UST) at different cooling rates. The microstructures of the alloys were composed of primary Si, eutectic Si, (Al,Si)3(Zr,Ni,Fe), Al9FeNi and Al3(Cu,Ni)2 phases. The microstructural features, such as the size and aspect ratio of each phase, changed with UST and cooling rate, and accordingly, the elevated temperature strength at 350 oC was changed. The alloy with a high volume fraction of about 30 vol.% exhibited increased elevated temperature strength at 350 oC when ultrasonic melt treated, and the alloy having a volume fraction as low as about 18 vol.% exhibited the opposite results. Considering the microstructural features of the multi-component Al-Si alloy, a hexagonal shear-lag model was suggested, based on the well-known shearlag model proposed by Nardone and Prewo (Scr. Metall. 20;1986:43-48). Using the 2-D microstructural factors such as the size, aspect ratio of the phase and secondary dendrite arm spacing, the elevated temperature strength was calculated and compared with the measured value. Based on the hexagonal shear-lag model, the influence of microstructural factors on the elevated temperature strength was discussed for multi-component Al-Si-Cu-Ni alloys.

Effect of Ultrasonic Melt Treatment on Solidification Behavior of Al7SiMg Alloy

Effect of Ultrasonic Melt Treatment on Solidification Behavior of Al7SiMg Alloy

Role of Ultrasonic Melt Treatment in the Improvement of Corrosion Resistance of Al–7Si–0.4Mg Cast Alloy

Role of Ultrasonic Melt Treatment in the Improvement of Corrosion Resistance of Al–7Si–0.4Mg Cast Alloy

Effect of ultrasonic melt treatment conditions on melt quality of Al–Mg alloy

In this study, the effect and mechanism of ultrasonic melt treatment (UST) were studied to achieve high-quality molten Al–Mg alloy. The purpose was to analyze the change in the cleanliness of molten aluminum according to UST process conditions such as ultrasonic power, treatment duration, and stabilization duration for molten Al–Mg alloy, and to find the optimal ultrasonic process conditions to achieve high-quality molten aluminum. UST results were compared to the effect of the Gas Bubbling Filtration (GBF) process, which is a general molten aluminum treatment process. Density index, bifilm index, porosity, and X-ray CT analysis were used for quality evaluation of melt cleanliness. UST was performed at a frequency of 19.7 kHz and two outputs of 600 W and 1200 W after maintaining 1 kg of molten aluminum at 800 °C for 10 min. The UST treatment durations were 1, 3, and 5 min, the stabilization durations after treatment were 0, 10, and 20 min. Then the quality of the molten aluminum was measured. The GBF treatment was applied for 1, 5, 10, or 30 min under impeller rotation speed of 300 rpm and gas flow rate of 1 L/min. During UST, the melt quality improved as the ultrasonic power increased and the treatment duration increased. To secure the high melt quality, UST could obtain the required degassing effect after 3 min of treatment, whereas GBF treatment took 10 min. The bubble size generated by UST is smaller than that by GBF, so UST has higher mas transfer coefficient of hydrogen than GBF and hydrogen in the melt could be removed with only a short UST treatment. UST was superior to GBF immediately after treatment, however, the melt quality deteriorated during the stabilization after UST. It caused from the unstable oxide film and a relatively rapid high-temperature oxidation, so appropriate molten metal management and rapid post-processing are necessary after UST treatment.

Casting A356+SiCp with ultrasonically treated melts

Low mass fractions (0.05 wt%) of SiC micro sized particles have been added to an A356 melt and dispersed by ultrasonic vibration to study their impact on the microstructural morphology of cast samples. It is shown that the ultrasonic melt treatment at 680°C can promote a homogenized distribution of the reinforcement while also degassing the melt and induces a moderate grain refinement. Even though SiC may act as a nucleant, its use did not induce a significant grain refinement relatively to ultrasonically treated unreinforced melts. Adding SiC microparticles, however, seems to enhance Eutectic Si modification, although it contributes to its slight coarsening at the expense of Mg2Si.

Eutectic Phase Characterization and Mechanical Properties of Al-Cu Alloy Ingot Solidified with Ultrasonic Treatment.

An Al-Cu alloy ingot was produced with the application of ultrasonic melt treatment. The effects of ultrasonication on the grain structure, eutectic phase, solution, and tensile properties of the alloy were analyzed. The volume and distribution of the eutectic phase were quantitatively evaluated based on stereological theory. The results are as follows: The grain-refinement efficiency at the center, 1/2 radius and edge of the ingot is 33.99%, 45.2% and 41.68%, respectively, under the action of an ultrasonic field. Ultrasonics improves the solid solubility of the Al-Cu alloy element, in which the solid solubility of Cu increases from 0.85% to 1.42%. The ultrasonic field improves the dispersion degree of the eutectic phase and reduces the volume fraction and eutectic phase number per unit volume. The mechanical properties of the Al-Cu alloy were improved by an ultrasonic field.