Solute redistributions associated with nucleation and growth of α1plates in Cu–Zn and Au–Cu–Zn alloys (original) (raw)
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SEM and X-Ray Diffraction Studies On Microstructures in Cu-26.04%Zn-4.01%Al Alloy
Due to fact that Cu-based alloys are very sensitive to the thermal treatments, in scanning electron microscopy and X-ray diraction observations, according to the dierent quenching techniques Cu26.04%Zn4.01%Al alloys can display dierent product phases such as martensite and precipitation. Rapidly cooling sample was formed as M18R structure from the ordered DO3 phase and in the monoclinic case, β = 89.1 • determined for sample. It was seen that a α-precipitation (fcc) phase in the matrix is slowly cooling.
An analytical electron microscopic investigation of precipitation in an Al-Cu-Zn-Mg-Ag alloy
1993
The distribution, morphology, chemistry, and crystallography of the precipitates formed during aging of an Al-Cu-Zn-Mg-Ag alloy have been studied using analytical transmission electron microscopy. The first precipitates to appear during aging at 150°C were thin hexagonalshaped plate-like precipitates which formed on the {lll}Al planes. These precipitates had a facecentred orthorhombic crystal structure and their composition was essentially CuA1, although they contained a trace of silver. At peak hardness the microstructure consisted of the plate-like precipitates on {lll}Al planes and 0' precipitates on {lOO}A1 planes. Overaging resulted in the precipitation of equilibrium 8, CuAl,, which exhibited a lath morphology and a n orientation-relationship with the matrix (210)Al 1 I (llOIy; (OO1)A1 misoriented from (OOl), by-6". Prolonged overaging at 250°C resulted in the formation of cuboid-shaped Al,(Cu,Zn),Mg, precipitates which had a cubic crystal structure and a cube:cube orientation-relationship with the matrix.
Materials & Design
The volume fraction of age hardening precipitates upon peak ageing after different quenching rates has been studied for five Al-Zn-Mg-Cu alloys using small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). The rate of change in volume fraction of the η' age hardening precipitates as a function of cooling rate was used to evaluate changes in the degree of solute supersaturation, and hence the quench sensitivity of the Al-Zn-Mg-Cu alloys. The results demonstrate that the amount of η' age hardening precipitates can be changed by varying the thermomechanical processing history or the alloy compositions. It was found that the volume fraction of age hardening η' precipitates in Al-Zn-Mg-Cu alloys increases with increasing cooling rates and increasing Mg content as well as that the size of η'
The effect of Cu on mechanical and precipitation properties of Al–Zn–Mg alloys
Journal of Alloys and Compounds, 2004
The effect of Cu on the mechanical and precipitation properties of a high strength Al-2.4 at.% Zn-2.1 at.% Mg alloy was investigated by compression and indentation tests, as well as by differential scanning calorimetry (DSC), transmission electron microscopy (TEM) and three-dimensional atom probe field ion microscopy (3DAPFIM). The addition of 0.5 at.% Cu introduces significant changes in the precipitation process and consequently in the age-hardening behavior of the alloy. Microstructural measurements reveal that the addition of Cu changes the density of GP zones, but it also changes partly the shape and composition of the particles. Mechanical and microstructural results together lead to the conclusion that clustering of solute atoms and vacancies during or immediately after water quenching plays an important role in the nucleation of intermediate phase precipitates in one-step aging and the addition of Cu to ternary Al-Zn-Mg leads to changes also in the initial clustering process.
Materials Research, 2014
In this study, the effects of cobalt and nickel additions on microstructure evolution and mechanical properties of Al-Zn-Mg-Cu alloys produced by chill casting process were investigated. Al-Zn-Mg-Cu aluminum alloys containing Ni and Co additives were homogenized at different heat treatment conditions, aged at 120°C for 24 h, and retrogressed at 180°C for 30 min then re-aged at 120°C for 24h. Comparison of the ultimate tensile strength of the Al-Zn-Mg-Cu base alloy underwent RRA temper process with that of the base alloy underwent a similar heat treatment process after the addition of 0.5 wt. % Ni and 0.5 wt. % Co showed that the gains of tensile strengths of the orders of 100 MPa and 135 MPa were attained respectively. These improvements are attributed to phase dispersion particles of the formation of Ni and Co-rich such as Al 7 Cu 4 Ni, Al 75 Ni 10 Fe 15 , Al 3 Ni 2 and Al 70 Co 15 Ni 15. The dispersed particles of nickel or/and cobalt have improved the ultimate tensile strength to reach 630 MPa and 665 MPa and the hardness HV values to 250 MPa and 265 MPa respectively. Besides dispersion, Ni and Co intermetallic dispersoids retarded the grain growth, led to grain refinement and precipitation hardening and resulted in further strengthening of the Al alloy. Microstructure characterization of the alloys was carried out using optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD).
Quenching and ageing behaviour of quaternary Cu-Zn-Al-Ni single crystals
Le Journal de Physique IV, 2001
The ageing behaviour of the martensite in single crystals made from the quaternary alloy (Cu-9.04 at%Zn-20.87 at%Al-3.07 at%Ni) was investigated, together with a characterization of the structure and the microstructure in the initial condition. The long range ordering temperatures were determined by electrical resistivity measurements. The stabilization of stress induced martensite was quantitatively studied as a function of time and temperature. After performing the same thermal treatment as for the ageing experiments, slices for transmission electron microscopy were cut and the resulting structure and microstructure were analyzed. The high temperature (3 phase is long range ordered and the martensite has the 18R structure. No evidence for the appearance of y precipitates was found after a quench from 770 K. However, a large number of vacancy loops with straight borders lying in {1 0 0} planes were present, with the corresponding dislocations dissociated in partials. It was also found that the stabilization process takes place in the martensite, but with a slower kinetics than in Cu-Zn-Al.
Journal of Materials Science, 2013
The structures of two nanoscale plate precipitates prevalent at maximum strength and over-aged conditions in a 7449 Al-Mg-Zn-Cu alloy were investigated. Models derived from images of high angle annular dark field scanning transmission electron microscopy were supported by first-principles calculations. Both structures are closely linked to the g-MgZn 2 Laves phase through similar layers of a rhombohedral atomic subunit. The finest plate contains one such layer together with a layer of an orthorhombic unit. The second plate contains rhombohedral layers only, normally four, but rotated relatively to form different stacking variants, one of which may be likened to g. For both structures, the same atomic planes describe the main interface with Al. Both plates could be described in space group P3. The unit cells comprise interface and arbitrary numbers of {111}Al (habit) planes. Eight Al-planes were included in the firstprinciples calculations. The enthalpy indicates high layer/ unit stability. The plate thickness can be understood by a simple mismatch formulation.
Crystal Research and Technology, 1987
The effect of Mn additions (0 ... 2 wt%) on the decomposition of rapidly solidified Al-1.0 wtyo Cu alloys (cooling rate lo3 to lo4 K/s; LQ treatment) were studied during ageing 1 letween RT and 450 "C by hardness, X-ray methods and electron microscopy. The results were compared with alloys homogenized in the region of the solid solution (SQ treatment). (i) The LQ treatment results in a quite better homogeneous distribution of the aIIoyed < lements than the SQ one, t h a t is less particles of intermetallic phases are present in the as-. i nst state. (ii) A t T < 250 "C Mn additions affect the decomposition kinetics by trapping trf vacancies (retardation) and the diminution of the solubility of Cu atoms (acceleration). The first effect dominates in the stage of G.P. zone formation, the second one during preci-1)itation of intermediate phases. (iii) At T 2 300 "C the intermetallic compound Cu,Mn,Al,, Jorms associated with a significant increase of the hardness. Der EinflulS von Mn-Zugaben (0 ... 2 wt%) auf die Entmischung schnell kristallisierter 41-4.0 wt% Cu-Legierungen (Abkiihlgeschwindigkeit von lo3 bis lo4 K/s; LQ-Behandlung) wurde mittels HBrtemessungen, Rontgenmethoden und Elektronenmikroskopie whhrend .ler Alterung zwischen RT und 450 "C untersucht. Die Ergebnisse wurden mit Legierungen verglichen, die aus dem Bereich der homogenen festen Losung abgeschreckt wurden (SQ-Behandlung). (i) Die LQ-Behandlung ergibt eine wesentlich bessere homogene Verteilung der Legierungselemente im eingeschreckten Zustand als die SQ-Behandlung, d. h. es sind weniger Ausscheidungen intermetallischer Phasen vorhanden. (ii) Bei T < 250 "C beeinflussen die Mn-Zugaben die Entmischungskinetik durch Leerstelleneinfang (Verzogerung) und Verminderung der Loslichkeit der Cu-Atome (Beschl~unigung). Der erste Effekt dominiert im Bereich der Bildung von GP-Zonen, der zweite bei der Bildung von Zwischenphasen. (iii) Bei T 2 300 "C bildet sich die intermetallische Cu,Mn,Al,,-Phase, die eine bedeutende HBrteerhohung bewirkt.