Unrecrystallized Grains Research Articles

Tuning texture and precipitation using Y/Gd atomic ratio in iso-concentration Mg–Y–Gd–Ag–Zr extruded alloys

Three Mg–Y(–Gd)–Ag–Zr alloys with an iso-concentration of total alloying elements but different Y/Gd atomic ratios were hot extruded at 350 °C and their microstructures and mechanical properties were comparatively studied. Extruded Mg–2.4Y–0.4Ag–0.1Zr (at.%) base alloy shows a bimodal-grained structure composed of fine equiaxed recrystallised grains and coarse elongated unrecrystallised grains and has a 011¯0//ED (extrusion direction) texture. In contrast, when Y is partially replaced with Gd, extruded Mg–1.6Y–0.8Gd–0.4Ag–0.1Zr (at.%) and Mg–0.8Y–1.6Gd–0.4Ag–0.1Zr (at.%) alloys with the Y/Gd atomic ratio of 2 and 0.5, respectively, exhibit a near fully recrystallised structure and have a [0001]//ED texture. While basal γ″ precipitates dominate but few β′ precipitates form in Mg–2.4Y–0.4Ag–0.1Zr alloy, a large number density of both β′ and γ″ precipitates form in Mg–1.6Y–0.8Gd–0.4Ag–0.1Zr and Mg–0.8Y–1.6Gd–0.4Ag–0.1Zr alloys after post-extrusion ageing. Precipitation in the Gd-containing alloys is considerably enhanced by partial substituting Y with Gd. The peak-aged Mg–1.6Y–0.8Gd–0.4Ag–0.1Zr alloy keeps a relatively good balance between grain boundary strengthening, dispersion strengthening and precipitation hardening and thus obtains a good combination of strength and ductility, whose room temperature tensile yield strength, ultimate tensile strength and elongation are 377 MPa, 479 MPa and 8.0%, respectively.

Modeling of flow behavior and microstructure evolution for Mg-6Gd-5Y-0.3Zr alloy during hot deformation using a unified internal state variable method

The hot deformation behavior of Mg-6Gd-5Y-0.3Zr alloy at the temperatures of 673–748K and the strain rates of 0.01–1.0s−1 were investigated by hot compression experiments. On this basis, a physically based internal state variable (ISV) model coupling the microstructural evolution was established, in which the ISVs of the model included dislocation density, grain size and volume fraction of dynamic recrystallization (DRX). Besides, the recrystallized and un-recrystallized grain sizes were considered to characterize the evolution process of microstructure. By comparing the calculated and experimental flow stresses, the model was proved to be reliable. Then the model was imported into the finite element analysis (FEA) software ABAQUS to predict the ISV evolution of Mg-6Gd-5Y-0.3Zr alloy in the hot extrusion process. The comparative analysis of the simulation and experimental results further verified the applicability of the constitutive model established in this study.

Mechanical behavior in boron-microalloyed CoCrNi medium-entropy alloy studied by in situ high-energy X-ray diffraction

A single-phase face-centered cubic (fcc) CoCrNi medium-entropy alloy (MEA) with different boron-doping contents (30–1600 ppm) was fabricated by vacuum arc melting, then followed by cold rolling. It was found that the boron-doping in the CoCrNi MEA results in an obvious partial recrystallization and significant refinement of grain size. The tensile yield strength (YS) and ultimate tensile strength (UTS) are 0.94 GPa and 1.17 GPa with the ductility of 26% in 800 ppm boron doping alloy, which was attributed to the strengthening effect of the large unrecrystallized grains. The tensile YS and UTS is dramatically increased up to 1.35 GPa and 1.48 GPa with the ductility of 11% for in 1600 ppm boron doping alloy. In this study, our results demonstrate that the uneven structure can be accomplished effectively by a proper boron addition and the enhancement of mechanical properties is mainly attributed to the unrecrystallized grains microstructure and grain refinement resulting from microalloying with boron by in situ high-energy X-ray diffraction (HE-XRD) technique. This offers a new perspective in interpreting the heterogeneity of structural materials and its influence on mechanical behaviors.

Achieving ultra-high strength in Mg–Gd–Ag–Zr wrought alloy via bimodal-grained structure and enhanced precipitation

Mg–13.1Gd–1.6Ag–0.4 Zr (wt%) alloy was either iso-thermally extruded at 350 °C or differential-thermally extruded with respectively pre-heated billet at 500 °C and die at 350 °C. The iso-thermal extrusion leads to a near fully recrystallized structure and a [0001]//ED (extrusion direction) texture. In contrast, the differential-thermally extruded alloy develops a bimodal-grained structure composed of fine equiaxed recrystallized grains and coarse elongated unrecrystallized grains with a 011¯0//ED texture. The differential-thermally extruded alloy has a higher number density of precipitates after post-extrusion ageing than that of the iso-thermally extruded counterpart. Moreover, precipitation in the differential-thermally extruded alloy is further enhanced with cold rolling before ageing. Finally, the alloy obtains room temperature tensile yield strength of 421 MPa and ultimate tensile strength of 515 MPa via differential-thermal extrusion, cold rolling and ageing, mainly ascribed to the coupled strengthening from the bimodal-grained structure and enhanced precipitation. Strength of the alloy is noticeably higher than those of Mg–Gd(–Y)–Ag extruded alloys with similar compositions reported previously and is comparable to those of other high-strength Mg wrought alloys. The findings suggest that differential-thermal extrusion plus strain ageing is a suitable approach for achieving high strength in age-hardenable Mg alloys.

Microstructural characteristics of AZ31 alloys rolled at room and cryogenic temperatures and their variation during annealing

• AZ31 alloy was rolled at room temperature (RT) and cryogenic temperature (CT). • Cryorolling forms more side cracks owing to the reduced workability at CT. • Cryorolling induces a lower dislocation density and forms less twins than RT rolling. • SRX during subsequent annealing is less pronounced in the CT-rolled material. • The annealed CT-rolled material exhibits an inhomogeneous bimodal structure. This study investigates the microstructural characteristics of AZ31 Mg alloys rolled at room temperature (RT) and cryogenic temperature (CT) and the variation in their microstructure and hardness during subsequent annealing. Cryorolling induces the formation of more side cracks than does RT rolling, because of the reduction in the ability of the material to accommodate deformation at CT. Numerous {10–11} contraction and {10–11}-{10–12} double twins are formed in both the material rolled at RT and that rolled at CT, because the grains of the initial material are favorably oriented for {10–11} twinning under rolling. The RT-rolled material has a higher dislocation density than the cryorolled material, and more twins are uniformly distributed throughout the former material. As a result, static recrystallization during subsequent annealing is more pronounced in the RT-rolled material, which results in the formation of a highly recrystallized homogeneous microstructure after annealing. In contrast, the formed twins are predominantly present along the shear bands in the cryorolled material, as a result of which this material has an inhomogeneous bimodal structure containing a large amount of coarse unrecrystallized grains after annealing. The hardness of the annealed RT-rolled material is higher than that of the annealed cryorolled material owing to the finer grain structure of the former.

Effect of micro-alloying Ca on microstructure, texture and mechanical properties of Mg–Zn–Y–Ce alloys

Microstructure, texture and mechanical properties of Mg–5Zn-0.3Y-0.2Ce alloys with the addition of trace xCa (x = 0, 0.3, 0.6 wt%) were systematically investigated in this work. The results revealed that more secondary eutectic phases and smaller grain size of as-cast microstructure could be found with increasing Ca content. After hot extrusion, the Ca-free alloy showed a uniformly recrystallized grain structure, while the Ca-containing alloys possessed a bimodal grain structure composed of fine dynamic recrystallized (DRXed) grains with a size of several microns and un-recrystallized coarse grains. EBSD analysis showed that the three extruded alloys had a fiber texture of (0001) basal plane aligned with the extrusion direction. Texture intensity of the DRXed region was weaker than the deformed region. The extruded alloy with the addition of 0.6 wt% Ca exhibited the highest yield strength of 321MPa due to the smallest DRXed grain size, the deformed region with strong basal texture and dense nanosized precipitates.

Improvement of strength – ductility balance of B2-strengthened lightweight steel

The microstructure evolution and tensile properties of a newly designed Fe-21Mn-10Al-1C-5Ni (wt.%) lightweight steel subjected to two annealing conditions (inducing partial recrystallization and full recrystallization) and subsequent aging treatment have been investigated. In the as-annealed condition, the microstructure of the steel consists of polygonal B2 particles along grain boundaries of recrystallized austenite grains and plate-shape B2 particles within unrecrystallized austenite grains, with no B2 bands. In addition, there is a formation of nano-sized κ-carbide and D03 particles within austenite grains and B2 particles, respectively. Subsequent aging promotes the formation of intragranular κ-carbide and D03 nanoparticles within austenite grains and B2 particles, respectively. As a result, the present steel shows an ultrahigh yield strength of 1.6 GPa after aging, which is mainly due to the presence of fine B2 particles within austenite grains and along grain boundaries as well as the additional strengthening effect of nano-sized κ-carbide and D03 particles present in austenite grains and B2 particles, respectively. The steel possesses good ductility (total elongation of 20%) even at such an ultrahigh strength level in the as-aged condition, surpassing the tensile properties of other B2 and κ-carbide strengthened lightweight steels.

Compositional optimization of Mg–Zn–Sc sheet alloys for enhanced room temperature stretch formability

Effects of scandium (Sc) content on microstructures and mechanical properties of a Mg–1.5Zn (wt.%) alloy have been systematically investigated. Mg–1.5Zn alloys with Sc content no more than 0.3 wt% showed large index Erichsen (I.E.) values, an indicator of stretch formability, over than 8 mm due to weak basal textures. Further increase in Sc content up to 1.5 wt% led to a gradual decline in the stretch formability and a Mg–1.5Zn–1.5Sc alloy showed the lowest I.E. value of 4.2 mm. Detailed microstructural characterization of the Mg–1.5Zn–1.5Sc alloy revealed that the poor stretch formability was associated with a combined effect of strong basal texture, un-recrystallized matrix grains and a dense distribution of ScZn and Sc second phase particles. On the other hand, tensile properties, in particular tensile yield strength (TYS) and r-value were almost identical along the rolling direction (RD) and the transverse direction (TD) for a Mg–1.5Zn–0.1Sc alloy. Higher TYS and r-value along the RD than the TD were observed in a Mg–1.5Zn–0.3Sc alloy, while opposite results were obtained in Mg–1.5Zn–1.0Sc and Mg–1.5Zn–1.5Sc alloys. Different plastic anisotropy trends observed in Mg–1.5Zn–xSc (x = 0.1–1.5) alloys could be ascribed to their distribution of crystallographic orientations.

Evolution of microstructure, texture, and mechanical properties in a multi-directionally forged ZK60 Mg alloy

An extruded ZK60 magnesium alloy with the nominal composition of Mg–6Zn–0.5Zr was processed by multi directional forging (MDF) for 2, 4, 6 and 8 passes at 473 K. Microstructural studies showed that the uniform microstructure of the as-extruded material transforms to a duplex structure consisting of fine recrystallized grains surrounding some patches of unrecrystallized grains after 2 and 4 passes of MDF. Further MDF passes, however, resulted in a homogeneous equiaxed structure in such a way that the as-extruded grain size of 12.7 μm was refined to 1.9 μm after 8 passes. Evaluation of crystallographic texture revealed that deformation by MDF changed the conventional fiber texture of the extruded condition to a new texture, in which the basal planes tend to align almost 45° to the transverse direction. Mechanical properties of the extruded and MDFed samples were studied by shear punch testing (SPT) at room temperature. The results indicated that the 182.6 MPa shear yield stress (SYS) and 184.9 MPa ultimate shear strength (USS) of the extruded condition were, respectively, reduced to 170.0 and 172.3 MPa after 2 passes of MDF. This drop in strength is attributed to the presence of coarse patches of unrecrystallized grains. Further pressing of the alloy was accompanied by a decrease in the volume fraction of coarse grains and an increase in the number density of fine grains. Textural softening that occurred at higher strain levels of the final MDF passes, however, offset the strengthening effect of these fine grains.

Significant improvement in the strength of Mg-Al-Zn-Ca-Mn extruded alloy by tailoring the initial microstructure

Mg-4.8Al-4.9Zn-2.3Ca-0.3Mn alloy was extruded using two different billets with coarse and refined initial microstructures, respectively. The extruded alloy using the coarse billet exhibits a good combination of strength and ductility among the reported Mg-Al-Ca and Mg-Zn-Ca alloys, while that using the refined one yields an increase of 66 MPa in tensile yield strength with little ductility loss. This distinct improvement is mainly attributed to the increased dispersion strengthening by the finer and more evenly distributed second particles. In addition, such particles assist in the formation of both ultrafine dynamically recrystallized grains and intense basal texture un-recrystallized grains which can also contribute to the incremental strength.

Improved Recrystallization Resistance of Al–Cu–Li–Zr Alloy through Ce Addition

The effects of the addition of 0.29 wt % Ce on the recrystallization behavior of an Al–Cu–Li–0.13Zr (wt %) alloy during isothermal annealing were investigated. Ce addition greatly improved inhibition of recrystallization in this alloy compared with that in the Ce-free alloy. The texture of the Ce-containing alloy contained a large amount of β-fibers and fibrous unrecrystallized grain microstructures distributed along the rolling direction in the overall annealing process. The improved recrystallization resistance endowed by Ce addition can be attributed to the large number of small Al8Cu4Ce species formed on the grain boundary. These fine particles with high-temperature stability can exert a Zener pressure on the Al3Zr dispersoid-free grain boundary. The yield strength of the Ce-containing alloy increased significantly, to 38 MPa, and the fracture toughness improved by 56.28% compared with those of the Ce-free alloy. This work provides a convenient and economical method for enhancing the overall performance of an Al–Cu–Li–Zr alloy via recrystallization inhibition by Ce addition.

Microstructure analysis and low-cycle fatigue behavior of spray-formed Al–Li alloy 2195 extruded plate

Microstructure and low-cycle fatigue behavior of spray-formed Al–Li alloy 2195 extruded plate were investigated in this work. The spray-formed alloy after hot extrusion experiment was treated with solid solution treatment and artificial aging. Microstructure analysis indicated the aged plate was dominated by elongated unrecrystallized grains, and had a rolling-type texture along extrusion direction with the highest intensity at Brass component. The existence of T1 phase strengthened the alloy crucially, but δ′ phase was basically absent. Then, the fully-reversed strain-controlled low-cycle fatigue tests were conducted at total strain amplitudes ranging from 0.4% to 1.0% for samples along two orthogonal directions. The stress-strain hysteresis loops were acquired, and the cyclic stress response curves were derived. At low strain amplitudes (0.4–0.5%), the initial cyclic hardening was slight and followed by a cyclic stability, while at higher strain amplitudes (0.6–1.0%), the alloy merely presented a continuously increasing cycle hardening behavior. Moreover, the fatigue life model based on the total strain energy was built and found to be suitable to predict life. Finally, the fatigue fractography observation showed that the fatigue source is relatively concentrated and the fracture surface had typical fatigue striations at 0.5% strain amplitude, while multiple cracks originated on the sample surface and the final fracture zone showed a ductile characteristic at 1.0%. The deformed microstructure near fracture surfaces were observed, and it was found that the cyclic hardening and stability were closely associated with the interaction between moving dislocations and obstacles including (sub)grain boundaries and secondary phase particles against them.

Hierarchical microstructure design to tune the mechanical behavior of an interstitial TRIP-TWIP high-entropy alloy

We demonstrate a novel approach of utilizing a hierarchical microstructure design to improve the mechanical properties of an interstitial carbon doped high-entropy alloy (HEA) by cold rolling and subsequent tempering and annealing. Bimodal microstructures were produced in the tempered specimens consisting of nano-grains (∼50 nm) in the vicinity of shear bands and recovered parent grains (10–35 μm) with pre-existing nano-twins. Upon annealing, partial recrystallization led to trimodal microstructures characterized by small recrystallized grains (<1 μm) associated with shear bands, medium-sized grains (1–6 μm) recrystallized through subgrain rotation or coalescence of parent grains and retained large un-recrystallized grains. To reveal the influence of these hierarchical microstructures on the strength-ductility synergy, the underlying deformation mechanisms and the resultant strain hardening were investigated. A superior yield strength of 1.3 GPa was achieved in the bimodal microstructure, more than two times higher than that of the fully recrystallized microstructure, owing to the presence of nano-sized grains and nano-twins. The ductility was dramatically improved from 14% to 60% in the trimodal structure compared to the bimodal structure due to the appearance of a multi-stage work hardening behavior. This important strain hardening sequence was attributed to the sequential activation of transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP) effects as a result of the wide variation in phase stability promoted by the grain size hierarchy. These findings open a broader window for achieving a wide spectrum of mechanical properties for HEAs, making better use of not only compositional variations but also microstructure and phase stability tuning.

Impact of forging direction on the recrystallization behaviour of nickel base superalloy AD730 billet material at subsolvus temperatures

AD730™ is a newly developed Ni-based superalloy for turbine disk applications produced by cast and wrought processes. Conventional ingot-to-billet conversion is an expensive and very complex operation. Because of the difficulties to achieve a uniform strain for recrystallization, large unrecrystallized grains are retained along this process. Heterogeneities of grain size have a negative impact on subsequent forging processes as well as ultrasonic inspectability of the destination part. The main aim of this work is to analyse the impact of both forging direction (billet, cogging) and strain (ε = 0.3–2) on the microstructural evolution of AD730 at subsolvus temperatures from a semi-finished product (billet) under conditions representative of both cogging and hot forging operations. Special attention to the presence of large unrecrystallized grains was paid. Double truncated cones (DTCs) were hot forged at subsolvus temperatures followed by air cooling. SEM and EBSD analysis were conducted in the as-received (billet) and the as-forged conditions. AD730 alloy presents a complex microstructure characterized by the presence of large unrecrystallized grains, aligned in the billet direction, with remarkable differences in γ′ precipitates distribution as compared to recrystallized structures. The fine distribution of primary γ′ precipitates (pinning effect) plays a key role on grain size control but also on the recrystallization behaviour. Continuous dynamic recrystallization (CDRX) mechanism was found to be operating in the large unrecrystallized grains, promoting the formation intragranular DRX grains and the gradual recrystallization of these grains. Strain presents a strong effect on the microstructural evolution of AD730, increasing the recrystallization fraction and refining the structure. By contrast, no significant effect associated to the forging direction was found. Conditions representative of cogging operations (ε ≤ 0.6) at subsolvus temperatures were translated into large fractions of unrecrystallized structures (strain accumulation).

Quasi in-situ analysis of geometrically necessary dislocation density in α-fibre and γ-fibre during static recrystallization in cold-rolled low-carbon Ti-V bearing microalloyed steel

In the present study, cold-rolled low-carbon steel is annealed at three different conditions: 700 °C for 0 s, 800 °C for 0 s and 800 °C for 2 min at the heating rate of ~10 °C/s. Recrystallization behaviour on sample surface is studied using a heated stage Scanning Electron Microscopy and Electron Backscattered Diffraction. For the lower annealing temperature of 700 °C with no dwell, almost no recrystallization is observed and microstructure resembles the as-received deformed material with the exception of occasional sub-micron sized nuclei. For the annealing conditions of 800 °C 0 s and 800 °C 2 min, onset and evolution of recrystallization is observed in-situ as a function of the initial as-cold rolled texture. Slower recovery rate of alpha fibre than gamma fibre is observed and confirmed by lower drop in average geometrically necessary dislocation (GND) density for un-recrystallized alpha fibres (1.1E+14 m−2 for 700 °C 0 s, 1.4E+14 m−2 for 800 °C 0 s and 4.5E+14 m−2 for 800 °C 2 min) than for un-recrystallized gamma fibre grains (3.0E+14 m−2 for 700 °C 0 s, 6.2E+14 m−2 for 800 °C 0 s and 9.8E+14 m−2 for 800 °C 2 min) during annealing. Strong gamma texture in recrystallized matrix is found for annealing conditions of 800 °C 0 s and 800 °C 2 min. From TEM characterisation it was shown that sub-grain boundaries are decorated with fine precipitates (diameter d < 15 nm) of titanium‑vanadium carbides (Ti,V)C for the annealing condition of 700 °C 0 s, which suggests that these precipitates play a major overall role in retardation of the recrystallization kinetics.

On the Coupling between Recrystallization and Precipitation Following Hot Deformation in a γ-γ′ Nickel-Based Superalloy

Postdynamic recrystallization and γ′ precipitation during cooling from γ′ supersolvus temperature after hot compression were studied in the AD730 (AD730 is a trademark of Aubert et Duval Company in Paris, France) γ-γ′ nickel-based superalloy. Emphasis was on not only both phenomena as distinct mechanisms but also on their mutual influence in terms of physical mechanisms. The growth of γ′ precipitates is hastened in the unrecrystallized grains compared to the recrystallized ones. This could possibly be attributed to the higher dislocation content acting as high-diffusivity paths. Postdynamic recrystallization is not prevented by Smith–Zener pinning of the recrystallization front by the γ′ precipitates. Instead, the recrystallization front dissolves γ′ precipitates, which then reprecipitate discontinuously or continuously and coherently with the surrounding γ matrix in the recrystallized grains.

Recrystallization and mechanical properties of WE43 magnesium alloy processed via cyclic expansion extrusion

In this study, cyclic expansion extrusion (CEE), as a relatively new severe plastic deformation (SPD) process, is applied to a rare earth (RE) containing Mg alloy WE43. The effects of the processing temperature and the number of passes are also investigated. The results showed that dynamic recrystallization (DRX) occurred after CEE processing at 400°C, and a bimodal structure with ultrafine DRXed grains surrounded the unrecrystallized grains. However, the DRX at 330°C was retarded because of the existence of RE elements. The tensile tests showed that a simultaneous increase in the strength and the ductility of WE43 is obtained after CEE processing at 400°C via two passes. Furthermore, the highest ultimate tensile strength of 440 MPa was achieved after the second pass of CEE at 330°C, and the highest ductility of 21% was attained after the second pass of CEE at 400°C. The microhardness measurements showed that the hardness increased from HV 80 to HV 114 and HV 98 after two passes of CEE processing at 330 and 400°C, respectively. In conclusion, increasing the processing passes could increase the mechanical properties and the volume fraction of the recrystallized grains. Moreover, increasing the temperature reduced the strength and the microhardness even if the elongation increased.

γ′ precipitates with a twin orientation relationship to their hosting grain in a γ-γ′ nickel-based superalloy

In a polycrystalline γ-γ′ nickel-based superalloy, γ′ precipitates with a close-to-twin orientation relationship to their surrounding matrix (named T-type precipitates) are found in recrystallized grains located near specific unrecrystallized grains (named recovered grains). This type of γ/γ′ interface has not been reported in literature before. Inherited from the ingot conversion process, recovered grains are characterized by a high density of micrometric and close-to-coherent γ′ precipitates. Resulting from the interaction of the recrystallization front with the latter precipitates, the T-type precipitates appear to form onto the recrystallization front. The present paper details the crystallographic characteristics of the T-type precipitates.

Bimodal grain microstructure development during hot compression of a cast-homogenized Mg-Zn-Zr alloy

Hot deformation of a cast-homogenized ZK60 alloy was studied by compression at a temperature of 450 °C and a strain rate of 0.001 s−1 to investigate microstructural evolution. The deformed microstructure was characterized using electron backscatter diffraction (EBSD) and high resolution transmission electron microscopy (HRTEM). EBSD observations of the deformed microstructure showed that hot deformation of this alloy resulted in a bimodal grain microstructure consisting of large pancaked unrecrystallized dendrites surrounded by recrystallized equiaxed fine grains. HRTEM studies revealed the presence of nano-(Zn-Zr)-precipitates in the deformed microstructure. Due to the coherency of precipitates/matrix, the dislocations were pinned by the nano-precipitates inside the unrecrystallized grains and the dislocation motion inside the grains was impeded, hence, a substructure evolved. Consequently, dynamic recrystallization (DRX) was suppressed and deformation was concentrated inside the DRXed region.

Effects of hot extrusion and heat treatment on microstructure and properties of industrial large-scale spray-deposited 7055 aluminum alloy

The industrial large-scale 7055 aluminum alloy fabricated by spray forming technology was subjected to hot extrusion and heat treatment to achieve high strength and ductility. Microstructure of the as-deposited alloy indicates that higher density billets with equiaxed grains (20–40 μm) were fabricated rather than a typical dendritic microstructure of the as-cast alloy. The grains of the as-extruded alloy exhibit fibrous morphology, the original boundaries disappear and fined second phases with size about 0.5–5 μm distribute along with extrusion direction. Meanwhile, the defects could be eliminated by hot extrusion, which resulted in good strength as well as ductility. The ultimate tensile strength, yield strength and elongation of the as-extruded alloy are 345 MPa, 236 MPa and 18.5%, respectively. After heat treatment, the partial recrystallization is observed around the un-recrystallized grains and sub-grains. And the platelet/rod-shaped precipitates (MgZn2) show a uniform distribution in the matrix alloy. The alloy reaches the maximum tensile strength of 730 MPa after T6 temper treatment, associated with a fine precipitation (MgZn2). However, with further deepen aging degree (from T6 to T73 temper), the size of dominant precipitated phases (MgZn2) grows obviously, the grain boundary precipitates transform from continuous to individual ones and the width of precipitate free zone increases. The result shows that the alloy after T7X temper treatment exhibits higher electrical conductivity (>35 %IACS) and facture toughness (>25.6 MPa m1/2) although a 8%–17% reduction in strength compared with that at T6 temper.