Temporal evolution of precipitates in multicomponent Al–6Mg–9Si–10Cu–10Zn–3Ni alloy studied by complementary experimental methods
Introduction
The strength of Al alloys strongly depends on the size, distribution, and composition of nanosized precipitates, which are partially coherent with the Al matrix [1]. The optimal mechanical properties of Al alloys are usually achieved via aging-induced precipitation [2], [3], and the resulting age-hardened Al alloys are generally classified as Al–Cu (2xxx), Al–Mg–Si (6xxx), and Al–Zn–Mg–(Cu) (7xxx) alloys [4]. In Al–Cu alloys, the main precipitates correspond to the transition phases of θ-Al2Cu, which considerably increases their strength [5]. The strength of Al–Cu alloys can be further improved by the addition of various elements (such as Mg, Ag, and Li) due to their ability to efficiently form precipitates characterized by different phases and orientations [6], [7], [8]. The strength of the Al–Mg–Si system can be increased by the formation of a metastable precipitate of β-Mg2Si [9], while the Al–Zn–Mg system is strengthened by precipitating precursors of the equilibrium η-MgZn2 phase [10].
The concurrent formation of different types of precipitates in mixed Al alloys (such as 2xxx + 6xxx and 2xxx + 7xxx) can be used to further improve their mechanical properties. Since the presence of one precipitate type affects the behavior of other precipitates, several researchers have studied the interactions between different precipitate species in mixed Al alloys. Haeffner and Cohen [11] examined the formation of Guinier-Preston (GP) zones in Al–1.5Cu–2.2Zn (at%) alloy by conducting wide-angle X-ray diffuse scattering measurements. They found that Cu atoms formed monolayered {100}Al planes, while Zn atoms were arranged in 〈110〉Al strings adjacent to the Cu zones, which relaxed the strain between Cu and Al atoms. Wenner et al. [12] recently investigated the precipitation behavior of the mixed Al–Cu–Mg (2xxx)/Al–Zn–Mg (7xxx) alloy system via transmission electron microscopy (TEM) and density functional theory calculations and determined that it was possible to substitute Al with Zn atoms in the S-Al2CuMg phase as well as Zn with Cu atoms in the η-MgZn2 phase.
More recently, several members of our research group [13] investigated the microstructure and mechanical properties of the multicomponent Al–8Mg–9Si–10Cu–11Zn (wt%) alloy, which was designed via mixing various precipitate-forming elements. In contrast to commercial Al alloys, it exhibited excellent strength at temperatures lower than 200 °C, owing to the presence of microsized secondary phases (such as Mg2Si and Q-Al5Cu2Mg8Si6), nanosized precipitates (such as θ′-Al2Cu and Q-Al5Cu2Mg8Si6), and Zn clusters [13]. Yang et al. [14] reported that Al–4.1Mg–1.2Li–10.7Cu–11.0Zn (wt%) alloy, which contained large amounts of precipitate-forming elements exhibited higher room-temperature strength and ductility than those of high-entropy AlLiMgZnSn alloy. It is certain that various types of precipitates are formed in multicomponent Al alloys, which interact with each other and affect their mechanical properties. However, the precipitation behavior of such multicomponent Al alloys has not been examined in detail.
In this study, the precipitation behavior of the multicomponent Al–6Mg–9Si–10Cu–10Zn–3Ni (wt%) alloy was investigated during artificial aging. The structural and chemical compositional evolutions of the precipitates were characterized using correlative experimental techniques including hardness, electrical resistivity, and compression measurements as well as differential scanning calorimetry (DSC) and TEM. Based on these insights into the evolution of complex precipitates, the strengthening mechanism of the studied multicomponent alloy was suggested.
Section snippets
Experimental procedure
One kilogram of alloy melt was prepared by heating a mixture containing high-purity (99.9%) Al, Mg, and Zn metals and Al–25Si, Al–30Cu, and Al–10Ni master alloys to 800 °C in an induction melting furnace followed by degassing via ultrasonic melt treatment [15] for 1 min in the temperature range of 750–700 °C. The degassed melt was poured into a Cu mold with dimensions of 245 × 70 × 200 mm3, which was pre-heated to 150 °C. The dimensions of the resulting rectangular ingot were 180 × 30 × 50 mm3,
Thermodynamic calculations
Fig. 1 shows the alloy temperature plotted as a function of the solid fraction. The obtained curve corresponded to Scheil–Gulliver solidification and was acquired using Thermo-Calc software [17] and the TCAL3 database (the contents of all constituent elements and compositions of all possible phases were taken into account during calculations). The resulting curve suggests the formation of the δ-Al3CuNi, Mg2Si, and Si phases prior to the formation of the fccAl matrix (#2–4). Further, different
Conclusions
- (1)
The as-cast Al–6Mg–9Si–10Cu–10Zn–3Ni alloy consisted of various secondary phases, including δ-Al3CuNi, Mg2Si, Q-Al5Cu2Mg8Si6, Si, θ-Al2Cu, and hcp Zn. The solution treatment at a temperature of 440 °C caused the dissolution of the θ-Al2Cu and hcp Zn phases and transformed the Mg2Si phase into the Q-Al5Cu2Mg8Si6 phase. The chemical composition of the Al matrix after the solution treatment was Al–0.33Mg–0.91Si–3.53Cu–14.14Zn–0.33Ni (wt%).
- (2)
The matrix hardness of the studied alloy was increased with
Acknowledgement
This work was supported by the Main Research Program (PNK4560) funded by the Korea Institute of Materials Science and the Industrial Strategic Technology Development Program (10062304) funded by the Ministry of Trade, Industry and Energy.
References (34)
- et al.
Optimizing the strength and ductility of fine structured 2024 Al alloy by nano-precipitation
Acta Mater.
(2007) - et al.
GP-Zones in Al–Zn–Mg alloys and their role in artificial aging
Acta Mater.
(2001) - et al.
Influence of alloy composition and heat treatment on precipitate composition in Al–Zn–Mg–Cu alloys
Acta Mater.
(2010) - et al.
A hybrid aluminium alloy and its zoo of interesting nano-precipitates
Mater. Charac.
(2015) High resolution electron microscope observations on precipitation in Al–3.0% Cu alloy
Acta Metall.
(1975)- et al.
Microstructural evolution and age hardening in aluminium alloys: atom probe field-ion microscopy and transmission electron microscopy studies
Mater. Charac.
(2000) - et al.
Precipitation in an Al–Mg–Cu alloy and the effect of a low amount of Ag
Mater. Sci. Eng. A
(2016) - et al.
Combinative hardening effects of precipitation in a commercial aged Al–Cu–Li–X alloy
Mater. Sci. Eng. A
(2013) - et al.
Pre-precipitate clusters and precipitation processes in Al–Mg–Si Alloys
Acta Mater.
(1999) - et al.
Effect of natural aging on quench-induced inhomogeneity of microstructure and hardness in high strength 7055 aluminum alloy
J. Alloys Compd.
(2015)
The structure of G.P. zones in an Al–Cu–Zn alloy
Acta Metall. Mater.
Precipitation in a mixed Al–Cu–Mg/Al–Zn–Mg alloy system
J. Alloys Compd.
Effects of ultrasonic melt treatment and solution treatment on the microstructure and mechanical properties of low-density multicomponent Al70Mg10Si10Cu5Zn5 alloy
J. Alloys Compd.
Combined effects of ultrasonic melt treatment, Si addition and solution treatment on the microstructure and tensile properties of multicomponent Al–Si alloy
J. Alloys Compd.
The effect of precipitation on the Portevin-Le Chatelier effect in an Al–Zn–Mg–Cu alloy
Mater. Sci. Eng. A
Electron microscopical investigations on the precipitation of various h.c.p. phases in an Al–6.8 at.%Zn alloy
Acta Metall.
The formation and reversion of Guinier-Preston zones in an aluminium–6.7 at.% zinc alloy and the effects of small concentrations of magnesium and silver
Acta Metall.
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