Peak-aged Samples Research Articles

In vitro degradation behavior and biocompatibility of Mg–5.8 Zn–2.0 Yb–0.5 Zr alloy during aging treatment

Ytterbium (Yb) containing magnesium alloys have aroused extensive interests because of their excellent mechanical properties. Unfortunately, their potential biomedical applications as a biodegradable implant material remain uncertain to date. In this study, in vitro degradation behavior and biocompatibility of the newly developed Mg–5.8 Zn–2.0 Yb–0.5 Zr (wt.%, denoted as ZYbK620) alloy during aging treatment were investigated. The results reveal that the dimension and distribution of Yb containing phases act a significant role in biocorrosion resistance and biocompatibility of ZYbK620 alloys. The peak-aged sample with much finer and denser nanoprecipitates possesses the lowest corrosion rate and best integrity after long-term immersion. Further biocompatibility testing demonstrates that the alloys with different aging times all exhibit favorable cytocompatibility and hemocompatibility, suggesting that the ZYbK620 alloy can be a promising candidate for biomedical applications.

Individual and synergistic effects of Mn and Mo micro-additions on precipitation and strengthening of a dilute Al–Zr-Sc-Er-Si alloy

Dilute Al–Er-Sc-Zr-Si alloys strengthened by coherent Al3(Er,Sc,Zr)(L12) nanoprecipitates have excellent coarsening- and creep-resistance up to 400 °C. Herein, the effects of micro-additions of 0.25 at.% Mn and/or 0.10 at.% Mo to a dilute Al-0.08Zr-0.014Sc-0.008Er-0.09Si (at.%) alloy are investigated with respect to precipitate evolution and the resulting strengths after different aging treatments. Both Mn and Mo provide solid-solution strengthening, contributing to ambient-temperature strength, in addition to elevated-temperature creep resistance. L12-core-shell nanoprecipitates created upon aging at 400 °C exhibit Mn partitioning at the Sc- and Er-rich precipitate cores, and Mo throughout the precipitates. Manganese-modified L12-precipitates exhibit a higher number density (~7.5 × 1022 m−3 for peak-aged condition), while Mo-modified L12-nanoprecipitates display significantly improved coarsening-resistance. No notable synergistic effect of Mn and Mo additions strengthening upon isothermal aging at 400 °C are observed. Isochronal aging displays, however, that a Mo addition delays the formation of Al/Si/Mn-rich α-precipitates from 425 °C to 475 °C. Both Mn and Mo additions improve the creep resistance of the alloys at 300 °C. Manganese-bearing alloys exhibit a more significant effect, as it doubles the threshold stress compared to the Mn-free base alloy. This strong effect could be a result of fine α-precipitates (<20 nm) formed during the creep experiments at 300 °C for the peak-aged sample. The over-aged Mn-containing samples are less creep resistant due to coarsening of both existing L12-nanoprecipitates and the absence of fine α-precipitates formed during creep.

Response of mechanical properties and corrosion behavior of Al–Zn–Mg alloy treated by aging and annealing: A comparative study

The high strength Al–Zn–Mg plates were processed by combing the hot extrusion and cold rolling. Then, both the artificial aging and annealing were conducted to make a comparative study on the microstructure, mechanical properties, and corrosion resistance. The aged samples were composed of near-equiaxed grains attributed from the static recrystallization during solution process, and owned the main textures of Cube, Goss, Copper, S, and Brass. The precipitate followed the sequence of SSS → GP zone → η′ phase → η phase. With the increase of aging time, the grain boundary precipitations (GBPs) became coarse and discontinuous, and the width of precipitate free zones (PFZs) also increased. In annealed samples, the coarse and elongated grains were finally formed, and the volume fraction of recrystallization textures increased with the extension of annealing time. Moreover, the density of dislocations and the number of MgZn2 phase were both reduced during annealing. The tensile strength along 0° with rolling direction was always the highest in all aged and annealed samples, and the elongation achieved the highest values along 45°. Long-time aging slightly improved the planar anisotropy, while long-time annealing greatly improved the planar anisotropy. The peak aged sample showed a ductility loss of 21.96% during the slow strain rate test in 3.5 wt% NaCl, and a maximum depth of 214.59 μm in intergranular corrosion test. Compared to the annealed sample, the aged one exhibited the worse corrosion resistance due to the wide PFZs and continuously distributed GBPs.

Influence of Heat Treatment on Precipitation Behavior and Mechanical Properties of Extruded AZ80 Magnesium Alloy

By means of annular channel angular extrusion technology and solution treatment, the AZ80 supersaturated solid solution was prepared. The β-Mg17Al12 precipitate morphologies analysis along with its sizes and area fraction measurement was performed to investigate mechanical properties variation of alloy at various aging temperature. The results indicated that after solution treatment, the intergranular precipitate of as-extruded alloy was re-dissolved into the matrix, effectively decreasing the stress concentration, which was beneficial to the enhancement of elongation. At aging temperatures of 300 °C, Widmanstatten structure, lath-shaped precipitate, and intergranular precipitate were observed, while at 175–200 °C, cellular structure and oval-shaped particle were also identified. The morphology, area fraction, size of the precipitates, and PFZs (precipitate free zones) width worked together to affect the age-hardening behavior of the alloy. The strength and hardness of the peak-aged samples decreased with the increase in aging temperature, which is primarily attributed to the reduction in cellular structure area fraction and the corresponding increase in the interlamellar spacing, and the coarsening of the rhombus precipitate.

Microstructure and Mechanical Properties of Mg–2.0Gd–1.2Y–1.0Zn–0.2Zr Alloy

The microstructural evolution of Mg–2.0Gd–1.2Y–1.0Zn–0.2Zr (GWZK) alloy during homogenization and subsequent aging heat-treatment and the tensile properties of the peak-aged sample at various temperatures have been investigated. The phase transformation during homogenization, static precipitation during aging, and deformation mechanisms at 250 °C are systematically analyzed through XRD, TEM and EBSD measurements. The peak-aged GWZK alloy has good combination of strength and ductility at elevated temperatures owing to its high thermal stability by the LPSO phases distributed along the grain boundaries. The change (19 MPa) in the yield strength of peak-aged samples between RT and 250 °C is mainly related to easy gliding of dislocations on the non-basal planes due to the decrease in critical resolved shear stress of slip. Two strengthening models are applied to quantitatively describe the effect of $${\left\{11\stackrel{-}{2}0\right\}}_{\alpha }$$ precipitate plates on Orowan strengthening corresponding to RT and 250 °C. Ignoring changes in solid solution strengthening and grain boundary strengthening of the peak-aged sample caused by increasing temperature, the calculated reduction value (16.5 MPa) in macroscopic yield strength from RT (based on the basal slip mode) to 250 °C (based on the pyramidal slip mode) is in good agreement with the measured reduction value (19 MPa).

Strengthening by hierarchical-structured nanoparticles in powder metallurgy manufactured ODS ferritic alloy

Abstract The synergic strengthening of powder metallurgy ferritic alloy by hierarchical-structured nanoparticles was exploited with the aim to further enhance the elevated-temperature mechanical properties. The characteristics and heterogeneous nucleation of hierarchical-structured nanoparticles, as well as its influence on mechanical properties were investigated. A high number density of hierarchical nanoparticles with size of 5–13 nm were formed in the peak aged sample. The hierarchical nanoparticles were the co-precipitation products of Y–Al–O oxides, Ni(Al,Mn) intermetallic phase and Cu-rich clusters. Cu-rich clusters first heterogeneous nucleate at the pre-existing interface of bcc-Fe/oxide, and then Ni, Al and Mn diffuse outwards from the Cu-rich cluster, resulting in the heterogeneous precipitation of B2–Ni(Al,Mn) nanoparticles at the Cu cluster/bcc-Fe interface. With the growth of B2–Ni(Al,Mn) nanoparticles, the oxide/Cu-rich cluster/B2–Ni(Al,Mn) hierarchical-structured nanoparticles were formed. A coherent or semi-coherent nature was revealed between Y–Al–O/bcc-Fe, Y–Al–O/bcc-Cu, bcc-Cu/NiAl and NiAl/bcc-Fe. Owing to the lattice-strain field and the load transfer capability, the hierarchical-structured nanoparticles were accounted for the enhanced mechanical properties of ferritic alloy above 650 °C.

Effects of aging treatment on the precipitation behaviors and mechanical properties of Al-5.0Mg-3.0Zn-1.0Cu cast alloys

Abstract This study investigates the relationship between aging temperature on the precipitation behavior and mechanical properties of a gravity cast Al-5.0Mg-3.0Zn-1.0Cu (wt%) alloy. After solution treatment at 470 °C for 24 h, alloys were aged at 120, 150 and 175 °C. Upon analyzing the samples, the alloys displayed different age hardening behaviors due to the variations in aging temperature. An increase in aging temperature not only reduced the peak aging time significantly, but also changed the distribution of precipitates. Numerous GPII zones and T′ precipitates (precursors of T-Mg32(AlZn)49) were homogeneously distributed within matrix at a higher aging temperature and the volume fraction of T′ precipitates increased. Tensile test results for peak-aged samples determined that both yield strength (YS) and ultimate tensile strength (UTS) increased, while elongation (EL) decreased with increasing temperature. The increase in the YS can be attributed to the higher volume fraction of T′ precipitates caused by the higher aging temperature. Moreover, the impact toughness decreased (due to a continuous decrease in EL) as the aging temperature increased. By adjusting aging temperature from 120 to 175 °C, YS increased from 377 to 451 MPa, while EL decreased from 13.8% to 5.2%. After peak aging treatment at 150 °C, the alloy appears to possess optimal mechanical properties with YS, UTS, EL and toughness being 441 MPa, 496 MPa, 9.6%, and 8.1 J/cm2, respectively. These finding suggest that there are many potential advantageous applications for this alloy within automobile components requiring high strength and toughness.

Room temperature yielding phenomenon in extruded or/and aged Mg-14Gd-2Ag-0.5Zr alloy with fine-grained microstructure

A new phenomenon of tensile yielding plateau in the fine-grained age-type Mg-14Gd-2Ag-0.5Zr alloy is reported, which is closely related to the activation of mobile pinned-dislocations. The yielding plateau contributes ~6% strain in the peak-aged sample, while it contributes only ~2% strain in the extruded sample.

Ageing condition of tensile specimens: fracture behavior of notched Al2024 sheet under tensile loading

The effect of different (T6 and T8) heat treatments on tensile properties and fracture behavior of Al2024 in presence and absence of notch by means of microhardness, tensile tests and scanning electron microscopy were investigated. Tensile and hardness specimens were subjected to two different artificial ageing (T6 and T8 heat treatment) for various times. These included under ageing (UA), peak ageing (PA) and over ageing (OA). T8 heat treatment, which has a cold rolling between solutionizing and ageing in its steps, showed a higher value of hardness and yield strength in comparison with common artificial ageing of T6 heat treatment. In notched-tensile specimens, yield stress was found to increase up to the peak ageing condition with a simultaneously decrease in elongation at fracture. This behavior was converse at OA condition. Although introducing of notch increase the yield stress of samples under T6 and T8 conditions in comparison with un-notched samples, the notch strengthening phenomenon was observed only under T8 treatment. Despite of an enhancement in strengthening by applying notch on tensile samples, the elongation to failure was notably lessen in both notched-heat treated samples in comparison with un-notches ones. Also, it was confirmed that the toughness of notched samples of both heat treatments at PA condition were significantly lower than un-notched ones. Consequently, toughness decrement was considerably dominated by the role of deformability compared to strengthening factor, however, the presence of cold rolling in the process of heat treatment (T8) could reduce the harmful effects of notch by increasing the stress bearing capacity in contrary with T6 heat treatment. Moreover, inserting the mechanical properties of peak aged samples from the un-notched tensile test in Abaqus finite element software; the V-shaped notch tensile test was simulated and confirmed the experimental results. It was shown in SEM results that the presence of notch enhanced the contribution of cracked particles, compared to particle/matrix deboning and matrix deformation, therefore, the non-homogeneous distribution of fracture features confirmed the harmful effect of notch. In the following, the distribution of three fracture micro-mechanisms were homogeneous in un-notched samples, which demonstrated the superior values of toughness in smooth samples. The present finding sheds light on development of processing techniques to optimize the mechanical properties of Al 2024 alloy.

Revisiting the role of Zr micro-alloying in a Mg-Nd-Zn alloy

The effect of Zr addition on microstructures and their evolution during heat treatments of a Mg-Nd-Zn alloy was studied using various electron microscopy techniques. The addition of Zr not only provided heterogenous nucleation sites to refine grain sizes of Mg during solidification, but also influenced microstructural evolution upon solution treatment and aging. Zn2Zr3 precipitates were formed in Mg-2.7Nd-0.6Zn-0.5Zr (wt. %) during solution treatment at 798 K, inducing remarkable hardness increment of the alloy. Moreover, decrease in Zn concentration in Mg matrix due to formation of Zn2Zr3 precipitates increased the density ratio of β1-Mg3(Nd,Zn) prismatic rod precipitates to γ''-Mg7(Nd,Zn)3 basal plates in peak aged samples. In addition, significant strain generated between Zn2Zr3/Mg interfaces facilitates the heterogeneous nucleation of β1-Mg3(Nd,Zn) at interfaces.

Incoherent long period stacking ordered phases and age-hardening in Mg-Gd-Ga alloys

The intermetallic phases of as-cast and annealed Mg-5Gd-3.5Ga (at.%) alloys were characterized by means of electron microscopies. Coherent and incoherent 18R long period stacking ordered (LPSO) phases with α-Mg were observed in the alloys and the high diffusion coefficient of Ga was the key factor for the appearance of incoherent LPSO phases. Segregation and βF’ phases were observed in the peak-aged samples, which contributed to the large improvements of microhardness and compression properties after heat treatment. In addition, the GdMgGa phase with a hexagonal ZrNiAl-type structure was studied by transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). The incoherent LPSO phases provided a new way of strengthening the mechanical properties of Mg alloys instead of introducing dispersive LPSO phases only.

Effects of artificial aging on microstructure, mechanical properties and stress corrosion cracking of a novel high strength 7A99 Al alloy

A recently developed 7A99 Al alloy was subjected to hot extrusion, solid solution and artificial aging. The microstructure evolution and precipitation behavior were examined, and their effects on mechanical properties and stress corrosion cracking were analyzed. The results showed that the coarse Mg(Zn, Cu)2 phases were broken and refined by hot extrusion. Most of the phases dissolved into Al matrix during solution, and only insoluble Al7Cu2Fe phase was remained. GPI zones and η′ appeared in the under-aged and peak-aged samples. With the extension of aging time, stable η phase with large size formed and became the dominant precipitate in the over-aged sample. It was concluded that the precipitation of 7A99 Al during aging at 150 °C followed the sequence of solid solution → GPI zones → metastable η′ → stable η. The peak-aged sample owned the high yield and ultimate tensile strength of 588 MPa and 622 MPa, and a low elongation of 10.2%. The under-aged and over-aged samples exhibited relatively lower strength and higher elongations. 2% pre-stretching prior to aging could further improve the tensile properties. Both the under-aged and peak-aged samples were susceptible to the stress corrosion cracking, and the intergranular cracking was observed. In contrary, the over-aged sample showed much better corrosion resistance with a typical ductile fracture, due to the coarsening and separation of grain boundary precipitations.

Coarsening- and creep resistance of precipitation-strengthened Al–Mg–Zr alloys processed by selective laser melting

The coarsening behavior of Al3Zr precipitates during aging was investigated for two Al–Mg–Zr alloys (Al–3.6Mg–1.2Zr and Al–2.9Mg–2.1Zr, wt%) processed by selective laser melting (SLM). Scanning transmission electron microscopy (STEM) investigations of peak-aged (400 °C, 8 h) samples reveal both continuous (~2 nm in diameter) and discontinuous (~5 nm wide and hundreds of nanometers in length) coherent, secondary L12-Al3Zr precipitates. In-situ STEM experiments showed that aging at 400 °C results in the appearance and growth of both grain-boundary Al3Zr precipitates, and intragranular nanometer-sized spherical Al3Zr precipitates in Zr-rich dendritic arms. Heating to 500 °C resulted in the disappearance of most Al3Zr precipitates and oxide particles. This microstructural evolution sheds light on the evolution of the alloy strength at elevated temperature. For short-term yield tests, as-fabricated samples displayed higher yield strengths than peak-aged samples at temperatures above 150 °C (e.g., 87 vs 24 MPa at 260 °C). This is attributed to coarsening of grain-boundary precipitates during aging, decreasing their ability to inhibit grain-boundary sliding (GBS) of the fine equiaxed grains (~1 µm). For longer term creep tests at 260 °C, both as-fabricated and peak-aged samples displayed near-identical creep behavior during a long-duration (168 h) creep test; by contrast, during a shorter duration creep test (8 h), as-fabricated samples are more creep-resistant than samples previously aged at 260 °C (threshold stresses of ~40 vs. ~14 MPa, respectively). Again, the creep behavior is consistent with coarsening of grain-boundary precipitates, occurring now during long-duration creep tests at 260 °C. An exact creep mechanism could not be isolated due to microstructural changes during testing but is believed to be a combination of GBS and dislocation motion.

Evolution of the Second-Phase Particles and Their Effect on Tensile Fracture Behavior of 2219 Al-xCu Alloys

In this study, the continuous evolution of the second-phase particles across as-cast, homogenization, multi-directional forging (MDF), and solution-aging treatment and their effect on tensile fracture behavior of 2219 aluminum alloys with different Cu contents was examined by optical microscopy (OM), scanning electron microscopy (SEM), and tensile tests. The results showed that the microstructure of as-cast 2219 aluminum alloy consisted of the α-Al matrix, Al2Cu coarse phase, and Fe-rich impurity phase. Severe segregation of Cu existed, and eutectic networks can be observed in the ingot. With an increase in Cu content, the eutectic networks became coarsen and thicker. During the complex improved process, the refinement mechanisms were fragmentation, dissolution, and diffusion of Al2Cu particles. Most fine Al2Cu particles were fully dissolved into the matrix and partial coarse particles were still retained after solution-aging treatment. Thus, the elongations of all the samples, undergoing solution treatment followed by water quenching, increased evidently. Then, the elongations decreased slightly due to the increase of precipitates. The fractography analysis of peak aged condition samples indicated that the fracture mode was diverted from a typical inter-granular fracture to a mainly trans-granular fracture with increase in Cu content from 5.56% to 6.52%. Fracture initiation mainly occurred by original microcrack propagation and microvoid nucleation at the coarse constituents.

The combined effects of hydrogen and aging condition on the deformation and fracture behavior of a precipitation-hardened nickel-base superalloy

The effect of hydrogen (H) on the deformation behavior of Monel K-500 in various isothermal heat treatment conditions (non-aged, under-aged, peak-aged, and over-aged) was assessed via uniaxial mechanical testing. H-charged and non-charged specimens were strained to failure to facilitate a comparison of ductility, fracture surface morphology, strength, and work hardening behavior. For all examined heat treatment conditions, H charging leads to a significant reduction in ductility, which is accompanied by a consistent change in fracture surface morphology from ductile microvoid coalescence to brittle intergranular fracture. While H charging led to a systematic enhancement in the yield strength of all heat treatments, the three age-hardened conditions exhibited a more than 2-fold increase relative to the non-aged heat treatment. This suggests that H modifies the dislocation–precipitate interactions, which also manifest themselves through changes in work hardening metrics related to the dislocation storage and recovery rates. In particular, the H-charged peak-aged specimen exhibited a significant increase in initial hardening (dislocation storage) rate relative to the H-charged under-aged specimen. Transmission electron microscopy of these samples revealed the onset of widespread dislocation looping in the H-charged peak-aged sample, in addition to the planar slip bands characteristic of the non-charged condition. This result suggests that hydrogen induces the particle shearing-to-looping transition at smaller particle sizes. Possible mechanistic explanations for this observed behavior are presented.

Relationship between mechanical properties and age-hardening behavior around grain boundaries of Al-Mg-Si alloy

Nanoindentation tests were conducted near the grain boundary (GB) of the Al-Mg-Si alloy, and the influence of GB character on the aging precipitation behavior and the mechanical properties was confirmed. After obtaining the GB characters by electron back scattered diffraction (EBSD) analysis, nanoindentation tests were carried out on under-aged, peak-aged, and over-aged samples. And then, the indentation areas were observed by back scattered electrons imaging (BSE) in order to identify indentation positions with respect to the GB. In this study, for the GB character, focusing on the rotation angle, the high-angle GB (HAGB) and the low-angle GB (LAGB) were selected. In addition, coincident site lattice GBs (CSL) were selected as the special GB. In the 180°C under-aged samples, the nano-hardness near GB is higher than that far from GB, while 180°C peak-aged samples, the nano-hardness is lower than that far from GB. Then the range near the GB where the hardness changes was larger at HAGB than at LAGB and CSL3. This suggests that the GB character affects the aging precipitation behavior and mechanical properties.

Microstructural and ageing response assessment of eutectic Al-Cu alloy due to isothermal heat treatment in semisolid state

An as cast Al-33%Cu eutectic alloy has been processed by semisolid heat treatment, with the ultimate objective of developing a ductile and strong eutectic composite material for probable application as bearing materials and other sliding wear components. In this phase of work only microstructural characterises has been attempted. The as cast sample of Al–Cu alloy is subjected to isothermal heat treatment at a temperature of 560 °C for varying periods of time and followed by water quenched. The microstructures of the semisolid heat treated (SSH) samples are analysed using an optical microscope and scanning electron microscopy (SEM). The microstructures of the quenched Al-33%Cu alloy samples show lamellar to lamellar + dendritic transition after SSH treatment. The quenched microstructure after 20 min of holding time primarily consists of copper aluminide dendrites + supersaturated α–Al grains. A massive copper-aluminide (>80%Cu) intermediate phase is observed after 3 to 6 min SSH. The sample configuration did not change after semisolid heat treatment and water quenching. This suggest that complete remelting and overburning did not occur during the semisolid heat treatment. The SSH sample shows maximum hardness, after 10 min holding time compared to solution treated (at 560 °C) and aged (at 150 °C) sample of a standard Al-4.5%Cu cast alloy. The Transmission electron microscopy (TEM) micrograph of the as quenched 10 min. SSH sample shows rod shaped CuAl2 (θ) precipitates, a dislocation network, cellular subgrains and an extremely fine lamellar eutectic. Solute cluster probably Guinier–Preston (GP) zones, precipitates and fine α –Al grains was observed in the peak aged sample. The x-ray diffraction (XRD) analysis of aged SSH treated sample shows several intermetallic copper-aluminide phases in each sample.

Deformation assisted nucleation of continuous nanoprecipitates in Mg–Al alloys

Conventional aging of magnesium alloys results in a low number density of laths providing poor precipitate strengthening. We demonstrate that deformation driven precipitation (DDP) of Mg-Al (6 and 9 wt.%) alloys produces a high density of nanoprecipitates with small aspect ratios within grain interiors. Nanoindentation of these samples yields much higher hardness values compared to conventionally peak aged samples. The precipitate number density correlates with the dislocation densities observed in experiments and calculated using a strain hardening model. We argue that dislocation multiplication increases the number of heterogeneous precipitate nucleation sites and thereby enhances precipitation.

Dynamic Compression Behavior of a Mg–Gd-Based Alloy at Elevated Temperature

The dynamic compression behavior and microstructure evolution at 400 °C of an extruded Mg–8Gd–4Y–Nd–Zr alloy with different tempers were investigated. The peak-aged samples exhibit the highest compressive strength, followed by as-extruded samples and over-aged samples. The highest dynamic compressive strength of 582 MPa was achieved by peak-aged sample compressed at 1224 s−1. The high strength was attributed to the formation of abundant thermally stable βʹ precipitates and some dynamic precipitates. The dynamic compressive strength of peak-aged sample and over-aged sample is not sensitive to strain rates, while that of the as-extruded sample is sensitive to strain rates. The dynamic compressive strength of the as-extruded alloy can reach 535 MPa when compressed at 2024 s−1. The high strength was mainly ascribed to the formation of numerous dynamic precipitates and the work hardening effect caused by dislocations. The cracks are composed of crack that is 45° to loading direction on the cylindrical surface and crack on the compressed surface. Microstructure observation indicates that the crack was easily propagated along the interface between the adiabatic shear band and matrix, grain boundaries. The equilibrium phase β in over-aged sample was unable to hinder the crack propagation.

Quantified contribution of β″ and β′ precipitates to the strengthening of an aged Al–Mg–Si alloy

It is generally believed that β″ precipitates, rather than β′ precipitates, are the major strengthening precipitates in aged Al–Mg–Si alloys. The reason for this difference is not well understood. To clarify this, two samples of the same Al–Mg–Si alloy but with different aging states were prepared. The under-aged sample only contains nano-precipitates of the β″ type, while the peak-aged one contains nearly equal volumes of β″ and β′ precipitates. We have, for the first time, separated the strengthening effect of the contribution from βʺ and βʹ precipitates, respectively, by an indirect approach based on high-precision measurements of volume fractions, number densities, sizes, proportions of the precipitates, their lattice strains, the composition and grain size of the matrix. The β′ precipitates, which take 45.6% of the total precipitate volume in the peak-aged sample, contribute to the entire precipitation strengthening by only 31.6%. The main reason why they are less useful compared to β″ precipitates has been found to be associated with their smaller lattice strains relative to the matrix, which is 0.99% versus 2.10% (for β″).