Effect Of 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-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.

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.

Effect of Ultrasonic Melt Treatment on Solidification Behavior of Al7SiMg Alloy

Effect of Ultrasonic Melt Treatment on Solidification Behavior of Al7SiMg 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.

Effect of Ultrasonic Melt Treatment on Solidification Microstructure of Al–5Ti–1B Alloy Containing Numerous Inoculant Particles

Effect of Ultrasonic Melt Treatment on Solidification Microstructure of Al–5Ti–1B Alloy Containing Numerous Inoculant Particles

Effect of ultrasonic melt treatment on the microstructure and tensile properties of Al-25% Si alloy assisted by phosphorus addition

Abstract The effects of ultrasonic melt treatment (UST) on the microstructure and tensile properties of Al-25% Si alloys with and without phosphorus addition were investigated. The average size of the primary Si firstly decreased and then increased with the rise of the ultrasonic intensity. The minimum value is about 25.4 and 32.8 μm when the ultrasonic intensity is 900 W with phosphorus addition and 1 200 W without phosphorus addition. The average number of primary Si per unit area firstly increased and then decreased in both alloys with increasing of ultrasonic intensity. Both tensile strength and elongation were improved mainly due to the refinement of microstructure by UST. Finally, the mechanism of UST on the primary Si is discussed.

Numerical modelling and experimental validation of the effect of ultrasonic melt treatment in a direct-chill cast AA6008 alloy billet

In this work, we study how ultrasonic cavitation melt treatment (UST) affects the temperature distribution, sump profile, and resulting microstructure in the direct-chill (DC) casting of an AA6008 aluminum alloy. Two 152 mm diameter billets were cast; one was treated with UST (UST-DC casting) in the hot top while the other was not (conventional DC casting). To investigate the temperature distribution, temperature was measured at multiple points in both billets. The sump profile was visualized by pouring Zn into the sump during casting. The microstructure was analyzed by measuring the grain size of as-cast billets. A numerical model of DC casting and UST-DC casting has been validated with the temperature measurements across the billets, and the experimental results agrees well with the numerical model. It is found that the sump profile quantification with thermocouple measurements is more accurate and less prone to interpretation than with Zn tracing. Numerical simulation results show that UST application in the hot top with sonotrode position at 20 mm above the graphite ring level depresses the liquidus isotherm but does not affect the solidus isotherm, resulting in a thinner transition region compared with conventional DC casting. Grain structure analysis verifies that structure refinement with UST has been achieved at the given sonotrode position. The strongest grain refinement was at the center of the billet with the average grain size 50% smaller than that without UST. The results are discussed in terms of the known mechanisms of UST, i.e. dendrite fragmentation and deagglomeration of nucleating substrates.

Hierarchical refinement of primary phases in a multicomponent Al-14Si-CuNiMg casting alloy by ultrasonic melt treatment

The combined effects of ultrasonic melt treatment (UST) with the cooling rate on the microstructural evolution in a multicomponent Al-14Si-CuNiMg casting alloy was investigated. UST was applied to a melt at 800°C, followed by casting into a steel step mold at cooling rates in the range of 4-32 K/s. UST in the fully liquid state significantly reduced the sizes of the primary phases (the phases formed before Al) crystallized in the initial stage of solidification, and the structural refinement by UST became more pronounced for a faster cooling. With trace additions of Ti, V and Zr, the primary phase is most likely (Al,Si)3(Zr,Ni,Fe), and primary Si and then Al3Ni are sequentially formed upon solidification. AlP particles, well-known nucleants for primary Si, were also found to exist inside the (Al,Si)3(Zr,Ni,Fe) and Al3Ni which exhibited a very low lattice misfit with AlP (~0.7 and 4.7%, respectively). This importantly suggests that AlP can nucleate all the primary phases while it has the highest efficiency of structural refinement by UST for (Al,Si)3(Zr,Ni,Fe) phase that first nucleated in the molten metal. The nucleation of the primary phases was quantified using an analytical model based on exponential statistics. The hierarchical refinement operated by UST is further discussed.

Effect of ultrasonic melt treatment on the tribological behavior of 7075 aluminum alloy

Abstract In this study, the tribological properties of 7075 aluminum alloy produced by ultrasonic melt treatment (UST) are investigated. Tribological properties of untreated and ultrasonically treated samples under dry and lubricated sliding conditions were analyzed experimentally by the block on ring test method. Worn surfaces of untreated and ultrasonically treated samples were scanned by 3D optical profilometer and analyzed to search out wear characteristics in the material. Furthermore, microstructural examinations were conducted to investigate the beneficial effects of UST on the microstructural properties of the alloy using optical and scanning electron microscopy. According to the results obtained, UST refines the α-Al phase of the alloy and disperses precipitates to grain boundaries more uniformly. Also, hardness and density of the alloy increased through the effect of UST. Due to these favorable effects, the wear resistance of the alloy increased and the worn surfaces of the ultrasonically treated samples exhibited lower surface roughness according to 3D surface roughness measurements.

Effect of ultrasonic melt treatment on the tribological behavior of 7075 aluminum alloy

Abstract In this study, the tribological properties of 7075 aluminum alloy produced by ultrasonic melt treatment (UST) are investigated. Tribological properties of untreated and ultrasonically treated samples under dry and lubricated sliding conditions were analyzed experimentally by the block on ring test method. Worn surfaces of untreated and ultrasonically treated samples were scanned by 3D optical profilometer and analyzed to search out wear characteristics in the material. Furthermore, microstructural examinations were conducted to investigate the beneficial effects of UST on the microstructural properties of the alloy using optical and scanning electron microscopy. According to the results obtained, UST refines the α-Al phase of the alloy and disperses precipitates to grain boundaries more uniformly. Also, hardness and density of the alloy increased through the effect of UST. Due to these favorable effects, the wear resistance of the alloy increased and the worn surfaces of the ultrasonically treated samples exhibited lower surface roughness according to 3D surface roughness measurements.

Mechanism of ultrasound-induced microstructure modification in Al–Zr alloys

This work probes the effect of ultrasonic melt treatment (UST) on primary intermetallic particles and α-Al using pure Al and Al–Zr alloys (Al–0.3Zr–0.1Ti, Al–0.5Zr, Al–0.5Zr–0.5Mg–0.9Si) solidified at various cooling rates of 0.2–70 K s−1. The application of UST is shown to decrease the size and increase the number density and volume fraction of D023-structured primary Al3Zr and Al3(Zr,Ti) particles with a high nucleation potency for α-Al formation. High-resolution transmission electron microscopy analysis reveals that the cavitation-induced wetting and dispersion of γ-Al2O3 inoculant particles contribute to the refinement of primary intermetallic particles. The grain size of Al–Zr alloys increases with increasing cooling rate because of the concomitantly reduced formation of primary intermetallic inoculant particles. The UST-induced refinement of primary Al3Zr particles and the increased number density lead to grain refinement in Ti-free Al–Zr alloys. For the Ti-containing Al–Zr alloy, UST-induced grain refinement is achieved only at a very low cooling rate of 0.2 K s−1, possibly because of the side effects of UST on the growth-restricting influence of Ti. The fast cooling–induced solidification enables significant age-hardening by L12-Al3Zr nanoprecipitation (~5 nm) and is not affected by UST. Thus, this study shows that UST can be used to reduce the degree of grain coarsening of age-hardenable Al–Zr alloys at high cooling rates.

The effect of ultrasonic melt treatment on solid solution treatment temperature and/or time for an Al-7Si-2Cu-1Mg alloy

ABSTRACT Ultrasonic melt treatment (UST) is known for refining microstructures including intermetallic compound (IMC)s, and it is expected that the microstructural benefits induced by UST may reduce the time and temperature of solid solution treatment (SST). The effect of UST on SST for an Al-7Si-2Cu-1 Mg alloy was investigated in terms of changes of volume fraction of IMCs in connection with the tensile properties. The results show that UST not only refined the constituent phases but also reduced the volume fraction of IMCs in the as-cast microstructure, which promoted dissolution of Cu and Mg rich IMCs during SST, increasing the yield strength of the alloy. In addition, the SST time to achieve maximum strength was shortened by UST. Without UST, the strength was maximised at 520 °C for 8 hours, while with UST the strength was maximised at 2 ~ 4 hours. The dissolution of the constituent phases upon SST was also discussed.

Effects of high-intensity ultrasound on the microstructures and mechanical properties of ultra-large 2219 Al alloy ingot

The microstructural refinement of ultra-large 2219 Al alloy ingot is particularly important towards improving the corresponding mechanical properties for special industry application. Combined with the direct-chill casting, scalable high-intensity ultrasonic melt treatment (USMT) technique was applied to manufacture the ultra-large 2219 Al alloy cylindrical ingot (1380 mm in diameter and 4600 mm in length) in the present work. Then, the effects of USMT on the major microstructural constituents (i.e. primary α-Al grains, eutectic networks and precipitating particles) were investigated accordingly. The industry-level experiments showed that the major microstructural constituents were modified after introducing ultrasound. The primary α-Al phase was refined from the center part to the edge part compared with the ingot without USMT. The agglomeration of coarsening eutectic phase was mitigated and large lamellar eutectic networks became discontinuous from half radius to the edge part with USMT. Meanwhile, the mechanical properties of the solidified Al alloy ingots were also tested and compared between the samples with and without USMT. To reveal the modification of major microstructural constituents, the dominant mechanisms were proposed based on the ultrasonic cavitation and acoustic streaming.

Effect of ultrasonic melt treatment on intermetallic phase formation in a manganese-modified Al-17Si-2Fe alloy

Hypereutectic Al-Si based alloys are important automotive materials. Both manganese (Mn) addition and ultrasonic melt treatment (USMT) have each proved to be effective in modifying the embrittling platelet-like δ-Al3FeSi2 and β-Al5FeSi intermetallic compounds (IMCs) in these alloys. However, previous studies have identified no clear synergy in combining Mn addition with USMT to control these IMCs. This work presents a systematic study of the individual and combined effects of different levels of Mn addition and USMT on the formation of Fe-containing IMCs in an Al-17Si-2Fe alloy. Increasing the Mn content without USMT resulted in macro-segregation and formation of coarse IMCs. In addition, not all δ-Al3FeSi2/β-Al5FeSi IMCs transformed into the desirable α-Al15(Fe,Mn)3Si2 IMC. In contrast, the combination of USMT and Mn addition avoided all these issues. The resultant microstructure was featured by fine dispersed polyhedral α-Al15(Fe,Mn)3Si2 phase particles. The volume fraction of the IMCs was quantified and compared with predictions made from the Scheil equation and the equilibrium lever rule. In the absence of USMT, neither the Scheil equation nor the lever rule method offered reasonable predictions. Conversely, the measured volume fraction of the Fe-containing IMCs with USMT closely agreed with the lever rule predictions. The underlining mechanisms for the effect of Mn and USMT on Fe-containing IMC formation and the effect of USMT alone on the Fe-containing IMC selection were discussed and proposed.

Combined Effects of Ultrasonic Melt Treatment and Cu/Mg Solute on the Microstructure and Mechanical Properties of a Hypoeutectic Al-7Si Alloy

The effect of Cu/Mg solute combined with ultrasonic melt treatment (UST) on the microstructure and mechanical properties of a hypoeutectic Al-7Si alloy was investigated. Cu up to 4 wt pct and Mg to 1 wt pct were added to the alloy and UST was performed at about 100 °C above the liquidus temperature. UST at such a high temperature was ineffective in refining grain sizes but enhanced the microstructural homogeneity of the alloys with the refinement of α-Al secondary dendrite arm spacing (SDAS). It was found that both the grain size and the SDAS were solute sensitive: In the Al-7Si alloy with UST they insignificantly changed with Cu but decreased with an increase in Mg content. Along with the structural refinement, UST was likely to affect the solute redistribution and the subsequent formation of secondary phases (e.g., eutectic Si and Cu/Mg-rich intermetallic compounds (IMCs)). Quantitative analysis indicated that UST had significantly minimized microsegregation of Cu and Mg solutes, decreasing the amount of the IMCs finely and uniformly distributed. The underlying reason was attributed to the reduction in the size of the SDAS, which enabled the solid-state diffusion to occur more efficiently upon solidification. The most significant increase in the tensile properties was achieved for the Al-7Si-2Cu-1Mg alloy with UST where the SDAS was well refined and the grain size was the smallest among the alloys investigated. The important role of UST on the casting structure refinement and the solute distribution is discussed and the resulting mechanical properties are further explored.

Prediction of Cavitation Depth in an Al-Cu Alloy Melt with Bubble Characteristics Based on Synchrotron X-ray Radiography

The size of cavitation region is a key parameter to estimate the metallurgical effect of ultrasonic melt treatment (UST) on preferential structure refinement. We present a simple numerical model to predict the characteristic length of the cavitation region, termed cavitation depth, in a metal melt. The model is based on wave propagation with acoustic attenuation caused by cavitation bubbles which are dependent on bubble characteristics and ultrasonic intensity. In situ synchrotron X-ray imaging of cavitation bubbles has been made to quantitatively measure the size of cavitation region and volume fraction and size distribution of cavitation bubbles in an Al-Cu melt. The results show that cavitation bubbles maintain a log-normal size distribution, and the volume fraction of cavitation bubbles obeys a tanh function with the applied ultrasonic intensity. Using the experimental values of bubble characteristics as input, the predicted cavitation depth agrees well with observations except for a slight deviation at higher acoustic intensities. Further analysis shows that the increase of bubble volume and bubble size both leads to higher attenuation by cavitation bubbles, and hence, smaller cavitation depth. The current model offers a guideline to implement UST, especially for structural refinement.

Effect of Ultrasonic Melt Treatment on Microstructure and Mechanical Properties of 35CrMo Steel Casting

Effects of different power ultrasonic on microstructure and mechanical properties of 35CrMo steel casting were investigated using optical microscopy (OM), scanning electron microscopy (SEM) and hardness testing. A self-developed experiment apparatus was used for the propagation of ultrasonic vibration into the 35CrMo steel melt to carry out ultrasonic treatment. The experimental results showed that compared to the traditional casting, ultrasonic treatment can obviously change the solidification microstructure of 35CrMo steel, which is changed from coarse dendrites to fined dendrites or equiaxed grains. With the increase of ultrasonic power, equiaxed crystal is remarkably refined and its area is broadened. The micro porosity percentage of ingot casting decreases significantly and the porosity defects can be suppressed under ultrasonic treatment. The mechanical properties of 35CrMo steel ingot after heat treatment were enhanced by ultrasonic treatment: the maximum tensile strength is improved by 8.4% and the maximum elongation increased by 1.5 times.

Synergistic effect of ultrasonic melt treatment and fast cooling on the refinement of primary Si in a hypereutectic Al–Si alloy

A mechanism describing the synergistic effect of ultrasonic melt treatment (UST) and subsequent fast cooling on the refinement of primary Si particles in a hypereutectic Al−Si alloy was investigated by examining inoculant particles via high-resolution transmission electron microscopy, serial sectioning, and melt filtration. The application of UST activated non-wetting MgAl2O4 particles with diameters of ∼0.5 μm to nucleate the primary Si phase. The cavitation-enhanced wetting of MgAl2O4 particles caused the formation of the AlP phase at the MgAl2O4 interface, further improving the nucleation potential. The cavitation-enhanced wetting and dispersion of inclusions (such as MgAl2O4) also resulted in the refinement and de-agglomeration of AlP particles. The UST-induced changes to the inoculant particles ultimately increased their number density, and the observed effects became more pronounced after increasing the degree of undercooling up to 20 K, leading to enhanced refinement of primary Si particles at higher cooling rates (up to 102 K s−1).

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

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, macro-segregation 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 non-uniform 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 macro-segregation 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 reduction in the size of the primary δ-Al3FeSi2 particles which ensures the complete transformation of most primary δ-Al3FeSi2 particles to the peritectic β-Al5FeSi phase.