Microstructure modification for 2219 Al alloy through ultrasonic treatment and fast cooling

Abstract

The combined effects of ultrasonic treatment and fast cooling on the bulk hydrogen content, the refinement of α-Al grains and θ-Al₂Cu precipitated phase in the 2219 Al alloy were investigated in this work. Results showed that under the combined effects of ultrasonic treatment and liquid nitrogen cooling, the bulk hydrogen content was dramatically reduced. Metallography and scanning electron microscopy results indicated that both the α-Al grains and θ-Al₂Cu precipitated phase were greatly refined under the combined effects of ultrasonic treatment and liquid nitrogen cooling. Correspondingly, the 2219 Al alloy sample exhibited excellent mechanical properties due to the refinement of α-Al grains and θ-Al₂Cu precipitated phase as well as the low bulk hydrogen content.

Keywords

2219 Al alloy ultrasonic treatment fast cooling bulk hydrogen α-Al grain mechanical properties refinement

Introduction

2219 Al alloys have been widely used as structural materials in the aerospace industry due to their excellent mechanical properties and good weldability under a wide temperature range [1]. The microstructural modification during the solidification process plays a key role in improving the mechanical properties of 2219 Al alloys [2]. According to previous researches, the modification can be achieved through chemical inoculation [3,4] and physical treatment, such as mechanical stirring, electromagnetic stirring, rapid solidification and ultrasonic vibration [5 –8]. Among these methods, ultrasonic treatment (UT) has been proven to have great potential for its high efficiency in refining the microstructure and improving the mechanical properties [9 –11].

Wang [12] has observed a fine and uniform grain structure in an Al-2Cu alloy by ultrasonic treatment. Kotadia [13] has found similar results in an Al-10%Cu alloy under ultrasonic treatment. The refinement effect of UT on the microstructure of alloys mainly relies on ultrasonic cavitation and acoustic streaming [9]. Usually, UT was applied in the liquid or slurry zone of the melts to promote homogeneity, degassing, mixing, grain refinement, multiscale segregation mediation, and amelioration of eutectics/intermetallics [8,14]. However, after the withdrawal of the ultrasonic rod, it still needs a long time for the melt to be cooled to the ambient temperature. During this period, low cooling rate may lead to the generation of pores, cracks, macro-segregations and inhomogeneous distribution of microstructures as well as solutes, which will deteriorate the mechanical properties of the alloy. According to the athermal heterogeneous nucleation theory, the size of the inoculant particles is inversely proportional to the degree of undercooling [14,15]. Hence, the combined effects of UT and fast cooling processes are probably conducive for the solidification of Al melt. This hypothesis has been confirmed by the refinement of primary Al₃Ti intermetallic in an Al-0.4Ti alloy via UT and rapid quenching [16].

In order to investigate the effect of a faster cooling rate on the solidification of the Al-Cu alloy, an extreme cooling condition applying liquid nitrogen was utilised in this work. This can help the researchers to understand the initial or in-situ state of the Al-Cu melts, especially the evolution of the precipitated phase, which was seldom reported. The combined effects of the ultrasonic treatment and cooling types on the refinement of α-Al grains and precipitated phase in the 2219 Al alloy was investigated in this study. In particular, the degassing capacity of the UT and liquid nitrogen cooling (LNC) was characterised by the bulk hydrogen content of the solid 2219 Al alloy sample. The mechanical properties of the 2219 alloy sample were also determined to verify the favourable influence of UT and LNC.

Experimental

Casting procedures and materials

Figure 1 displays the schematic diagram of the experimental equipment. The ultrasonic system consists of a 2 kW generator, an air-cooled piezoelectric 20 kHz transducer, an ultrasonic amplitude transformer, and a titanium acoustic sonotrode with a tip diameter of 50 mm. The main experimental material was 2219 Al alloy with its chemical compositions Al-6.20Cu-0.36Mn-0.11Zr-0.1V-0.10Fe-0.06Si-0.01Mg-0.10Zn-0.05 wt-% Ti.

Figure 1

Schematic illustration of the experimental equipment.

For each batch of the experiment, 1.5 kg alloy was melted at 710°C in a SiC-graphite crucible inside an electrical resistance furnace. After mechanical stirring and isothermal holding for 30 min, the crucible with the melt was transferred to a platform with the ultrasonic equipment. For the first group of experiments, the preheated sonotrode was immersed 20 mm below the top melt surface. Ultrasound was performed for 8 min and terminated above the solidus, then the sonotrode was withdrawn and the crucible was naturally cooled in the air. A contrast experiment was carried out but with preheated idle rod (IR) without vibration, and the crucible was also air cooled (AC). For the second group of experiments, after 8-min ultrasonic treatment, the sonotrode was withdrawn and the crucible with the sample was immediately immersed (without submersion) into liquid nitrogen and all the other procedures were as same as the first group. A contrast experiment with preheated idle rod and LNC was carried out. The sample names and the corresponding experimental conditions are listed in Table 1.

Table 1

Experimental conditions for the samples.

Sample names	# Sample IR-AC	# Sample UT-AC	# Sample IR-LNC	# Sample UT-LNC
Ultrasonic vibration	without	With	without	with
Cooling type	AC	AC	LNC	LNC

Characterisation

The representative specimens for bulk hydrogen content measurement, microstructural examination and tensile test were taken from four different ingots, where the locations and dimensions of the samples are shown in Figure 2. The hydrogen measurement sample was abraded or milled to remove surface contamination.

Figure 2

Schematic diagram showing the sampling positions and dimensions.

All the metallographic samples were ground and polished through standard metallographic techniques. Optical observations were carried out by a Leica microscope, and the samples were etched with Keller's reagent (95% H₂O, 2.5% HNO₃, 1.5% HCl, and 1% HF) in this procedure. For colorised metallography detection, all the samples were anodised using Barker's reagent (200 ml 32% HBF₄ in 800 ml distilled water) at 20 VDC for 30 s using a stainless-steel cathode. After that, a ZEISS optical microscope (Imager. A2 m) equipped with an automated Zeiss AxioVision image analyser was used under polarised light for microstructural investigation. Grain size was measured using a linear intercept method (ASTM 112-10) and the statistical analysis of the results was performed. The morphology of the precipitated phase was characterised by a scanning electron microscopy (SEM TESCAN, MIRA3 LMH/LMU) equipped with an energy dispersive spectroscopy (EDS). The tensile test samples were evaluated by an Instron 3369 Mechanical Testing Machine with a loading rate of 1 mm/min at room temperature. All the tests were performed thrice, and the mean value of the three results was used as the final result. The standard deviations were also calculated and showed in detail.

Results and discussion

Bulk hydrogen content

Figure 3 shows the macrostructure and optical micrographs of the samples. From the macro and optical graphs, large pores with a size up to 200 µm (marked by circles) can be seen even on the surfaces of the metallographic samples cooled in air. In the IR-LNC sample, though macro-pores resulting from solidification shrinkage still remained, gas porosity was significantly reduced. Pores were scarcely seen in the UT-LNC sample.

Figure 3

Macrostructure of the IR-AC sample (a), UT-AC sample (c), IR-LNC sample (e), and UT-LNC sample (g); optical graphs of the IR-AC sample (b), UT-AC sample (d), IR-LNC sample (f), and UT-LNC sample (h).

The presence of occluded bulk hydrogen would increase the potential generation of porosity. Hydrogen is readily absorbed in the molten Al melt during the solidification processing. In order to quantify the degassing capacity, a RHEN600 Hydrogen Determinator (LECO Corporation, USA) was employed to determine the bulk hydrogen content in the samples. The bulk hydrogen is determined through the difference of the thermal conductivity between hydrogen and the carrier gas (argon) when the sample is heated in the thermal conductivity cell equipped with a self-contained electrode furnace for fusion [17].

The bulk hydrogen contents of the four representative samples are shown in Figure 4. The bulk hydrogen content of the UT-AC sample was 0.38 ± 0.023 cm³/100 g, while that was 0.52 ±0.020 cm³/100 g for the IR-AC sample. Relatively, the degassing efficiency of UT was 26.92%. However, in the IR-LNC sample, the bulk hydrogen content was further reduced to 0.25 ± 0.020 cm³/100 g. In comparison with IR-AC sample, the degassing efficiency of LNC was 51.92%. The main reason for the improvement was due to the huge difference in cooling rate between air cooling and liquid nitrogen cooling. The cooling rate for liquid nitrogen cooling was measured up to 40–60°C/s, while it was 0.2–1.0°C/s for air cooling. When the casting was cooled in liquid nitrogen, the degree of undercooling was getting larger than that being cooled in air, and the heat together with gas bubbles was quickly released out from the melt. Researches have been verified that ultrasonic degassing is able to decrease the amount of dissolved hydrogen to 40–50% below the quasi-equilibrium concentration [8,18]. However, the melt will absorb hydrogen from the atmosphere back to the quasi-equilibrium level [19]. Thus, it is essential to aggrandise the cooling rate during the subsequent cooling stage. In the UT-LNC sample, bulk hydrogen content was reduced to 0.12 ± 0.019 cm³/100 g, and the degassing efficiency came up to 52.00% compared with IR-LNC sample.

Figure 4

Hydrogen measurement curves of (a) the IR-AC sample; (b) the UT-AC sample; (c) the IR-LNC sample and (d) the UT-LNC sample.

According to Eskin [8], as a bubble oscillates in the alternating sound field, it acts as a pump which extracts more and more hydrogen from the melt with each expansion. The bubbles therefore grow and subsequently float to the surface, releasing the hydrogen to the atmosphere. Afterwards, melt flows created by the ultrasound source (acoustic streaming and secondary flows) facilitate bubbles distribution and, hence, degassing. In addition, the heat transfer is promoted by LNC. Thus, the release of gas bubbles is accelerated and hydrogen is prevented from being absorbed back into the melt by LNC.

Microstructure of α-Al grains

Figure 5 compares the average size of α-Al grains and shows the colorised optical micrographs of the corresponding samples. Coarse dendritic α-Al grains with a large size up to 1524.40 µm can be seen in the IR-AC sample. After ultrasonic treatment, the size of the largest grain was reduced to 515.32 µm but still exhibited a dendritic morphology. In addition, a lot of pores can be seen in these two samples (marked by circles). The size of the largest coarse dendrites in the IR-LNC sample was 620.00 µm, and sporadic pores can be seen in the sample. However, most of the coarse dendrites were refined to fine equiaxed grains and pores were hardly observed in the UT-LNC sample. As shown in Figure 5 (a), the average size of α-Al grains in the UT-AC sample and IR-AC sample were 342.25 and 677.15 µm, respectively, and the refining efficiency of UT was 49.46%. In special, the average size of α-Al grains in IR-LNC sample (417.73 µm) was a slightly greater than the UT-AC sample (342.35 µm). Whereas, the average size of α-Al grains was reduced dramatically to 198.61 µm in the UT-LNC sample.

Figure 5

Average grain size of α-Al phase in the four representative samples (a); colorised optical micrographs of the IR-AC sample (b), the UT-AC sample (c), the IR-LNC sample (d) and the UT-LNC sample (e).

As to the UT-LNC sample, UT was performed directly in the nucleation stage of α-Al grains. The sharp collapse of cavitation bubbles produces a high-energy shock-wave or cumulative microjet, which can improve the wettability of impurity particles and hence activates them to become potent nucleation sites [20]. It has been reported that the TiAl₃, ZrAl₃, NbAl₃, and/or BTi₂ can serve as efficient nucleation sites [21 –23]. Therefore, the nucleation rate of α-Al grains is promoted by the ultrasonic cavitation during the solidification of Al melt. Moreover, strong fluid flow resulted from acoustic streaming can uniformly distribute the temperature field across the sample, thus hindering the growth of the α-Al grains [24]. Combined with the fast cooling of liquid nitrogen, the growth rate of the α-Al grains is further restricted, causing the average size of α-Al grains being refined to a large extent in the UT-LNC sample.

Microstructure of precipitated Al₂Cu phase

In order to quantify the refinement of θ-Al₂Cu phase, Image Pro Plus software was employed to analyse the area fraction of coarse θ-Al₂Cu phase with an area more than 100 µm². The area fraction of the coarse θ-Al₂Cu phase and the SEM-EDS analysis of the four representative samples are presented in Figure 6. From the EDS spectrum given in Figure 6(b), it can be basically determined that the precipitated phase is θ-Al₂Cu. In the IR-AC sample, the precipitated phase spread broadly along the grain boundaries since the α-Al grains were with a large size. Under the ultrasonic treatment, the shape of the precipitated phase in UT-AC sample became thinner but still exhibited as long strips. This was due to that the sonotrode has been withdrawn above the eutectic transformation temperature of θ-Al₂Cu phase (548.2°C) [25]. The precipitated phase could not be directly refined by cavitation-induced dendrite fragmentation [26]. For the IR-LNC sample, a lot of θ-Al₂Cu phase were scattered to a lower distribution area. LNC directly affected the growth stage of θ-Al₂Cu phase, and thus the agglomeration degree of θ-Al₂Cu phase was greatly reduced owing to the large cooling rate [27].

Figure 6

Area fraction of coarse precipitated phase (a); SEM micrographs of the Idle rod-AC sample (b), the UT-AC sample (c), the Idle rod-LNC sample (d), and the UT-LNC sample (e).

In the UT-LNC sample, a lot of spherical θ-Al₂Cu particles were generated. On the one hand, the α-Al grains were refined and more inerratic grain boundaries were offered, which meant Cu atoms will array orderly on the grain boundaries and the interfacial energy would be lowered [20,28]. Thus, Al₂Cu phase precipitated in more locations [28]. Meanwhile, the grain boundaries of α-Al phase turned discontinuous and thinner under ultrasonication, which resulted in the formation of thinner and smaller scattered precipitated phase on the grain boundaries. On the other hand, fast cooling of liquid nitrogen directly suppressed the agglomeration of θ-Al₂Cu phase, which further refined the θ-Al₂Cu phase. As is observed in Figure 6(a), the area fraction of coarse θ-Al₂Cu phase in the UT-AC sample and IR-AC sample were 4.55 and 6.45%, respectively. The θ-Al₂Cu phase was refined by 29.45% under ultrasonic treatment. The area fraction of coarse θ-Al₂Cu phase in the IR-LNC sample was 4.31%, which was refined by 33.18% in comparison with the IR-AC sample. In UT-LNC sample, the area fraction of coarse θ-Al₂Cu phase was reduced greatly to 3.27%.

Mechanical properties

The tensile test curves and mechanical properties of the Al alloy samples are shown in Figure 7. As observed, the elongation of IR-AC sample was 1.07%. After ultrasonic treatment, the elongation was increased to 2.93%, while it had a little decrease for the IR-LNC sample (2.05%). The UT-LNC sample exhibited a higher elongation (5.07%), which was improved by 373.83% as compared to the IR-AC sample. It is a pretty good proof that samples present a better ductility with finer grains and lower gas porosity [29]. The ultimate tensile strength (UTS) for IR-AC sample and UT-AC sample were 71.54 and 77.33 MPa, respectively. The yield stress (YS) for IR-AC sample and UT-AC sample were 52.23 and 60.11 MPa, respectively. Comparatively, after ultrasonic treatment, the UTS and YS were increased by 8.09 and 15.07%, respectively. As for the IR-LNC sample, the UTS and YS were 81.17 and 56.39 MPa, respectively, which were 13.46 and 7.96% higher than the IR-AC sample. Under the combined effects of UT and LNC, the UTS and YS were further improved to 84.26 and 62.61 MPa, respectively, which were enhanced by 17.78 and 19.19% compared with the IR-AC sample.

Figure 7

Tensile test curves of the four representative samples (a), and mechanical properties of the four samples (b).

Generally, the strength of the material is negatively correlated with the grain size. The agglomeration of coarse θ-Al₂Cu phase on the grain boundaries may cause the stress concentration, which will reduce the strength of the 2219 Al alloy [30,31]. Thus, the strength as well as the ductility can be increased with refined grain size [32,33]. In addition, the high hydrogen content may produce microcracks in the alloy and cause hydrogen embrittlement, which will impair the mechanical properties of the 2219 Al alloy [34].

As a result, the combined effects of UT and LNC can effectively refine the α-Al grains together with θ-Al₂Cu phase and reduce the bulk hydrogen content, which in turn improve the mechanical properties of the 2219 Al alloy.

Conclusions

The bulk hydrogen content in the 2219 Al alloy samples was decreased dramatically under the combined effects of ultrasonic treatment and liquid nitrogen cooling, with a value of 0.12 ± 0.019 cm³/100 g. Compared with the sample treated with idle rod and air cooling, the bulk hydrogen content was reduced by 76.92%.

Under the conditions of ultrasonic treatment and liquid nitrogen cooling, the average size of α-Al grains of the Al alloy samples was decreased from 677.15 µm (solidified with idle rod and being cooled in the air) to 198.61 µm, indicating that the α-Al grains were refined by 70.67%. In addition, the agglomeration level of coarse θ-Al₂Cu phase on the grain boundaries was also reduced, resulting in the area fraction of coarse θ-Al₂Cu phase being decreased to 3.27%. As compared to the sample with idle rod and air cooling, the θ-Al₂Cu phase was refined by 49.30%.

Ultrasonic treatment and liquid nitrogen cooling together can improve the mechanical properties of the 2219 Al alloy samples due to the refined α-Al grains and the θ-Al₂Cu phase as well as the low bulk hydrogen content.

Footnotes

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Li Zhang

Ripeng Jiang

References

Surekha

, Murty

, Rao

KP.

Comparison of corrosion behaviour of friction stir processed and laser melted AA 2219 aluminium alloy. Mater Des. 2011;32(8–9):4502–4508. doi: 10.1016/j.matdes.2011.03.033

Eskin

GI.

Effect of ultrasonic (cavitation) treatment of the melt on the microstructure evolution during solidification of aluminum alloy ingots. Z Metallkd. 2002;93(6):502–507. doi: 10.3139/146.020502

, Hage

, Liu

, Revealing heterogeneous nucleation of primary Si and eutectic Si by AlP in hypereutectic Al-Si alloys. Sci Rep. 2016;6(25244).

Nogita

, McDonald

, Tsujimoto

, Aluminium phosphide as a eutectic grain nucleus in hypoeutectic Al-Si alloys. Microscopy. 2004;53(4):361–369. doi: 10.1093/jmicro/dfh048

Patel

, Yang

, Mendis

, Melt conditioning of light metals by application of high shear for improved microstructure and defect control. JOM. 2017;69(6):1071–1076. doi: 10.1007/s11837-017-2335-5

Chen

, Zhang

, Liu

, Preparation of Mg-Nd-Zn-(Zr) alloys semisolid slurry by electromagnetic stirring. Mater Des. 2016;95:398–409. doi: 10.1016/j.matdes.2016.01.131

, Wang

, Qiu

, Cooling rate and microstructure of rapidly solidified Al-20 wt.% Si alloy. Mater Sci Eng A. 2006;417(1–2):275–280. doi: 10.1016/j.msea.2005.10.040

Eskin

, Eskin

DG.

Ultrasonic treatment of light alloy melts. Boca Raton: CRC press; 2014.

Eskin

GI.

Broad prospects for commercial application of the ultrasonic (cavitation) melt treatment of light alloys. Ultrason Sonochem. 2001;8(3):319–325. doi: 10.1016/S1350-4177(00)00074-2

10.

Eskin

, Eskin

DG.

Production of natural and synthesized aluminum-based composite materials with the aid of ultrasonic (cavitation) treatment of the melt. Ultrason Sonochem. 2003;10(4–5):297–301. doi: 10.1016/S1350-4177(02)00158-X

11.

Qian

, Ramirez

, Das

Ultrasonic refinement of magnesium by cavitation: Clarifying the role of wall crystals. J Cryst Growth. 2009;311(14):3708–3715. doi: 10.1016/j.jcrysgro.2009.04.036

12.

Wang

, Dargusch

, Qian

, The role of ultrasonic treatment in refining the as-cast grain structure during the solidification of an Al-2Cu alloy. J Cryst Growth. 2014;408:119–124. doi: 10.1016/j.jcrysgro.2014.09.018

13.

Kotadia

, Qian

, Eskin

, On the microstructural refinement in commercial purity Al and Al-10 wt% Cu alloy under ultrasonication during solidification. Mater Design. 2017;132:266–274. doi: 10.1016/j.matdes.2017.06.065

14.

Qian

Heterogeneous nucleation on potent spherical substrates during solidification. Acta Mater. 2007;55(3):943–953. doi: 10.1016/j.actamat.2006.09.016

15.

Quested

, Greer

AL.

The effect of the size distribution of inoculant particles on as-cast grain size in aluminium alloys. Acta Mater. 2004;52(13):3859–3868. doi: 10.1016/j.actamat.2004.04.035

16.

Wang

, Eskin

, Connolley

, Effect of ultrasonic melt treatment on the refinement of primary Al3Ti intermetallic in an Al-0.4 Ti alloy. J Cryst Growth. 2016;435:24–30. doi: 10.1016/j.jcrysgro.2015.11.034

17.

Zhang

, An

, Fukuyama

, Characterization of hydrogen-induced crack initiation in metastable austenitic stainless steels during deformation. J Appl Phys. 2010;108(6):063526. doi: 10.1063/1.3477321

18.

Eskin

, Alba-Baena

, Pabel

, Ultrasonic degassing of aluminium alloys: basic studies and practical implementation. Mater Sci Tech-Lond. 2015;31(1):79–84. doi: 10.1179/1743284714Y.0000000587

19.

Eskin

DG.

Ultrasonic processing of molten and solidifying aluminium alloys: overview and outlook. Mater Sci Tech-Lond. 2017;33(6):636–645. doi: 10.1080/02670836.2016.1162415

20.

Eskin

GI.

Principles of ultrasonic treatment: application for light alloys melts. Adv Perform Mater. 1997;4(2):223–232. doi: 10.1023/A:1008603815525

21.

Easton

, StJohn

DH.

A model of grain refinement incorporating alloy constitution and potency of heterogeneous nucleant particles. Acta Mater. 2001;49(10):1867–1878. doi: 10.1016/S1359-6454(00)00368-2

22.

Wang

, Qiu

, Liu

, The grain refinement mechanism of cast aluminium by zirconium. Acta Mater. 2013;61(15):5636–5645. doi: 10.1016/j.actamat.2013.05.044

23.

Wang

, Qiu

, Liu

, Crystallographic study of grain refinement of Al by Nb addition. J Appl Crystallogr. 2014;47(2):770–779. doi: 10.1107/S1600576714004476

24.

Hellawell

, Liu

, Lu

SZ.

Dendrite fragmentation and the effects of fluid flow in castings. JOM. 1997;49(3):18–20. doi: 10.1007/BF02914650

25.

Srivastava

, Chaudhari

, Qian

Grain refinement of binary Al-Si, Al-Cu and Al-Ni alloys by ultrasonication. J Mater Process Tech. 2017;249:367–378. doi: 10.1016/j.jmatprotec.2017.06.024

26.

Jung

, Lee

, Cho

, Combined effects of ultrasonic melt treatment, Si addition and solution treatment on the microstructure and tensile properties of multicomponent Al-Si alloys. J Alloy Compd. 2017;693:201–210. doi: 10.1016/j.jallcom.2016.09.006

27.

Jung

, Ahn

, Cho

, Synergistic effect of ultrasonic melt treatment and fast cooling on the refinement of primary Si in a hypereutectic Al-Si alloy. Acta Mater. 2018;144:31–40. doi: 10.1016/j.actamat.2017.10.039

28.

Aghayani

, Niroumand

Effects of ultrasonic treatment on microstructure and tensile strength of AZ91 magnesium alloy. J Alloy Compd. 2011;509(1):114–122. doi: 10.1016/j.jallcom.2010.08.139

29.

, Jian

, Meek

, Degassing of molten aluminum A356 alloy using ultrasonic vibration. Mater Let. 2004;58(29):3669–3673. doi: 10.1016/j.matlet.2004.02.055

30.

Ludtka

, Laughlin

DE.

The influence of microstructure and strength on the fracture mode and toughness of 7XXX series aluminum alloys. Metall Trans A. 1982;13(3):411–425. doi: 10.1007/BF02643350

31.

Shi

, Shen

, Mao

, Effects of ultrasonic treatment on microstructure and mechanical properties of 6016 aluminium alloy. Mater Sci Tech-Lond. 2018;34(12):1511–1518. doi: 10.1080/02670836.2018.1465514

32.

Hansen

Hall-Petch relation and boundary strengthening. Scripta Mater. 2004;51(8):801–806. doi: 10.1016/j.scriptamat.2004.06.002

33.

Kang

, Sun

, Deng

, High strength Mg-9Al serial alloy processed by slow extrusion. Mat Sci Eng A. 2017;697:211–216. doi: 10.1016/j.msea.2017.05.017

34.

Campbell

Castings. Oxford: Butterworth-Heinemann; 1993.

Microstructure modification for 2219 Al alloy through ultrasonic treatment and fast cooling

Abstract

Keywords

Introduction

Experimental

Casting procedures and materials

Characterisation

Results and discussion

Bulk hydrogen content

Microstructure of α-Al grains

Microstructure of precipitated Al2Cu phase

Mechanical properties

Conclusions

Footnotes

Disclosure statement

ORCID

References

Microstructure of precipitated Al₂Cu phase