Refinement Strengthening Research Articles

Aging hardening behavior and P texture formation of laser repaired GH4169 nickel-based alloy

Laser repair technology based on the DED principle is an advanced green remanufacturing technology that not only repairs the damaged parts but also restores their mechanical properties. Therefore, this technology has been widely used for the repair of key components in aircraft engine. However, due to the fact that the mechanical properties of the repaired zone are usually lower than those of the substrate, this limits the application of laser repair technology in the field of remanufacturing. Therefore, it is crucial to study the microstructure evolution and its influence on mechanical properties of the laser repaired object to improve the mechanical properties of the repaired zone and promote the widespread application of laser repair technology. In this study, the microstructure evolution and its effect on the aging hardening mechanism of laser repaired GH4169 alloy were investigated using SEM, EBSD and TEM techniques. The results show that the hardening mechanisms in the repaired zone are different from those in the substrate. The main hardening mechanisms in the repaired zone are strain hardening, elastic stiffness strengthening and aging hardening, while the hardening mechanisms in the matrix are grain refinement strengthening, aging hardening, strain hardening and texture strengthening. In addition, during the aging period, the texture of the matrix is mainly recrystallized Cube and Goss textures, while the texture of the repaired zone is mainly P texture, and the P grain nucleates and grows in the R-Copper grain.

Dependence of molybdenum content on the cavitation corrosion synergy and wear failure of laser cladded CoCrFeNiMnMo high entropy alloy coatings

The CoCrFeNiMnMo high entropy alloy (HEA) coatings with various Mo contents (0.1, 0.5, 0.8, 1.0 in atomic ratio) were prepared by laser cladding, aiming at determining the optimum Mo content and the effect of Mo on the microstructure and properties of CoCrFeNiMnMox HEA. The synergistic cavitation failure-corrosion impact of the coatings was also studied in 3.5 wt% NaCl solution. Experimental results showed that HEA coatings were only composed of FCC matrix and the grains were refined gradually with the increase of Mo contents. Meanwhile, the corrosion resistance of the coatings increased first and then decreased. The CoCrFeNiMnMo05 possessed the highest corrosion resistance as indicated by the highest polarization resistance, strongest passivation tendency and lowest carrier concentration. The wear resistance of the coatings was significantly higher than that of the substract. The enhanced wear resistance was contributed to the grain refinement and solid solution strengthening. After 8h cavitation failure, the CoCrFeNiMnMo05 showed the lowest mean depth failure of 0.05 μm as it maintains the highest self-healing ability and integrity of passive film during the synergistic effect of cavitation failure and corrosion. In this study, the optimum Mo content was determined and the effect of Mo on the microstructure and properties of CoCrFeNiMnMox HEA was described.

Analysis of abrasive impact wear of the Mn8/SS400 bimetal composite using a newly designed wear testing rig

In this study, the abrasive impact wear behaviour of a bimetal composite made of medium manganese steels (MMSs) and low carbon steels (LCSs), i.e., the Mn8/SS400 bimetal composite, was investigated using a newly designed wear-testing rig. The need for a new rig arose from the difficulty in replicating real-world wear conditions. Our rig allows for precise control and measurement of wear, simulating harsh environments more accurately than other wear-testing rigs. The bimetal composite Mn8/SS400 demonstrated superior wear resistance, showing an improvement of up to 2.8 times compared to benchmark steels, attributed to its enhanced work hardening sensitivity. Scanning electron microscopy (SEM), X-ray diffractometer (XRD), and electron backscatter diffraction (EBSD) analyses were employed to elucidate the wear mechanisms. After 300 h of abrasive impact wear, the subsurface microhardness of Mn8 reached 601.31 HV, significantly higher than that of the matrix hardness of 292.24 HV, indicating a substantial work hardening effect. The wear mechanism of the Mn8/SS400 bimetal composite was found to be a synergistic effect of grain refinement strengthening, dislocation strengthening, and twin strengthening. Initially, twin strengthening was the dominant mechanism up to 200 h of wear testing. However, after 300 h, contributions from all three mechanisms became increasingly significant, enhancing the overall wear resistance of the composite.

Cutting performance and wear mechanism of submicron and ultrafine Ti(C, N)-based cermets

The complex thermal-mechanical coupling among Ti(C, N)-based cermet tool, workpiece and chip affects immensely the tool life, machining quality and costs during high-speed cutting, which makes the investigation on wear mechanisms of tools quite important. In this work, submicron and ultrafine Ti(C, N)-based cermet tools were prepared by vacuum sintering technology, and the cutting performance of the tools was evaluated by continuous dry cutting. The aim of this work is to unravel the wear mechanisms of submicron and ultrafine Ti(C, N)-based cermet tools based on the cutting performance and wear characteristics of both the cutting tools and chips generated during high-speed cutting. The Vickers hardness, flexural strength and tool lifespan of ultrafine Ti(C, N)-based cermets are significantly superior to those of submicron Ti(C, N)-based cermets because of grain refinement strengthening and the improved distribution of metal phases. Tool wear depends to a large extent upon the contact states and heat transfer ability at different locations of the tool edge, which are characterized by simultaneous action and mutual transition from abrasive, adhesion, surface fatigue and oxidative wear. Overall, ultrafine Ti(C, N)-based cermet tools with excellent comprehensive properties exhibit a distinctly reduced tool wear at different wear regions.

Correlation of austenite grain size with ε-/α′-martensitic transformation and mechanical properties in a high-manganese damping steel

One of the core studies on low stacking fault energy (SFE) high-manganese steel is to maintain excellent damping capacity while achieving high strength and toughness. The austenite grain size (AGS) in high-Mn steel affects its SFE and even the strength-plasticity and damping capacity of the steel, but the detailed mechanism related to martensitic transformation has not been clarified. In this study, Fe-17Mn high-Mn damping steel is used as the material to obtain austenite grains of different sizes by controlling the cold rolling and annealing processes. By using in-situ tensile testing, damping capacity testing, and various microscopic analytical techniques, the influence of AGS on the thermal/deformation induced martensitic transformation, work hardening behavior, mechanical properties and damping capacity of the steel is mainly studied. The results indicate that the refinement of austenite grain increases the SFE of high-Mn damping steel and reduces the amount of thermal induced ε-martensite (εth) and stacking faults (SFs). The deformation induced martensitic transformations (DIMTs) in high-Mn damping steel during tensile deformation include γ→εD, εth→α′ and εD→α′ transformation. The deformation induced ε-martensitic transformation is more helpful to improve the work hardening rate than deformation induced α′-martensitic transformation. Due to the concentration of strain partitioning at grain boundaries, twin boundaries and phase boundaries, refinement of austenite grain can promote deformation induced ε-martensitic transformation and improve the steel strength. However, excessively small austenite grains can suppress deformation induced α′-martensitic transformation leading to a significant decrease in elongation. Under the synergetic effects of grain refinement strengthening and multiple martensitic transformations, when the average AGS is about 4.0 μm, the steel has high strength and high plasticity, with a tensile strength of 919 MPa, a yield strength of 518 MPa and an elongation of 46.4 %. The product of tensile strength and elongation is up to 42.6 GPa·%. At low or high strain amplitudes, the damping capacity of this steel shows an opposite trend with the refinement of AGS. The damping capacity of the steel gradually increases with grain refinement at low strain amplitudes of 0.01 %–0.065 %, mainly due to the reduction of the content of weak pinning points. At high strain amplitudes of 0.065 %–0.1 %, the damping capacity of the steel gradually decreases for the reduction of damping sources with the refinement of grain size.

Better mechanical properties of SAF2507 duplex stainless steel formed by cold rolling and normalizing

The SAF2507 duplex stainless steel with the heterogeneous structure is produced through cold rolling (ε = 90%) and subsequent 1-min normalizing at 1273 K. Compared with the corresponding initial samples, the grain sizes of ferrite and austenite phases in the 90%-1273 sample are refined by 90%, which led to an increase in the number of grain or phase boundaries between the two phases. The yield strength (YS) of the 90%-1273 sample increased to 715 MPa from 541 MPa, while the uniform elongation of 24.8% is slightly smaller than that of the coarse-grained sample. The higher YS is mainly contributed by the strengthening of grain refinement and dislocation strengthening by incorporating geometrically necessary dislocations (GNDs). During tensile deformation, the accumulation of GNDs in the heterostructured sample continuously generates hetero-deformation-induced (HDI) stress. The HDI stress plays a positive role in the 90%-1273 sample showing an ultimate tensile strength of 939 MPa. Additionally, the amount of twin boundaries in the 90%-1273 sample rose from 4.5% to 35% during tensile deformation, which indicated that the twinning induced plasticity effect was helpful in retaining the ductility of the 90%-1273 sample. This work provides strategies for optimizing the mechanical properties of duplex stainless steels and contributes to understanding the essence of a superior combination of strength and ductility of heterostructured materials.

Mn-controlled martensitic variant selection significantly affects the strength and toughness of 2.3 GPa ultra-high strength spring steel

In this study, the microstructure and mechanical properties of 55SiCrVNb ultra-high strength spring steel with 0.7 and 1.5 wt.% Mn were systematically investigated. The results show that 0.7Mn steel exhibited higher strength and toughness. The morphology and content of retained austenite, content of element in solid solution and the type and quantity of precipitates were basically the same in 0.7Mn and 1.5Mn steels. Hence, the variant reconstruction, as a unique perspective, was used to unravel the strengthening and toughening mechanisms governing the evolution of variants across varying Mn contents. Compared with the 1.5Mn steel, the decrease in Mn content deteriorated the variant selectivity (decreased variant frequency over 50 %), which led to a more uniform distribution of close-packed plane (CP) and Bain groups in 0.7Mn steel, thus refining the block size and improving the grain refinement strengthening (σp). The 0.7Mn steel with a higher density of high angle grain boundaries (HAGBs) effectively constrained dislocation slip, thereby enhancing dislocation strengthening (σd). As the Mn content decreased, the block size decreased from 0.24 to 0.14 μm, and the contribution of σp and σd increased by about 107 and 96 MPa, thus improving the yield strength. In addition, the increased HAGBs, which were dominated by the highly selective V1/V2, V1/V3(V5) and V1/V6 variant pairs, and the uniform CP and Bain group also contributed to inhibiting crack deflection and enhancing the impact toughness. Moreover, the higher Schmid factor with high geometrically necessary dislocation of 0.7Mn steel improved the deformation resistance of variants and strength. This work provided a new mechanism of strengthening and toughening dominated by variants.

Comprehensive study of microstructural evolution and strengthening mechanism of high-performance pure copper prepared by blue laser metal deposition (B-LMD)

The high absorption of the copper to the blue laser provides an alternative method to circumvent the laser reflection of laser metal deposition (LMD) of pure copper. In this work, blue laser metal deposition (B-LMD) was used to prepare pure copper parts. The B-LMD pure copper tracks fabricated using the optimum processing parameter have well bonding with the substrate, consisting of fine equiaxed grains with an average size of 2.8 μm, and exhibit the highest microhardness of 133.21 HV0.2. The pure copper deposit fabricated by the optimum processing parameter exhibited the highest relative density (97.9 % ± 0.2 %) and microhardness (103.05 ± 4.37 HV0.2). Additionally, the microstructure of the B-LMD pure copper deposit is showing a bimodal grain structure with columnar grains at the melt pool boundary and fine equiaxed grains at the center. The B-LMD pure copper deposit exhibits excellent mechanical properties, with an ultimate tensile strength of 244 ± 9 MPa, yield strength of 158 ± 6 MPa, and a fracture elongation of 14.7 ± 0.8 %. The superior mechanical properties are primarily attributed to grain refinement strengthening and dislocation strengthening. The high performance of B-LMD pure copper demonstrate the potential of the blue laser as an effective alternative energy source for fabricating high-performance pure copper components.

In-situ N-doping to improve wear and corrosion resistance of a complex-concentrated alloy manufactured by directed energy deposition

In this study, the effects of in-situ N-doping on wear and corrosion resistance of a complex-concentrated alloy (CCA) prepared by directed energy deposition have been studied. After the addition of N, the wear resistance of the CCA is significantly improved (wear rate: decreasing from ∼2.92 × 10−4 mm3/N•m to ∼0.68 × 10−4 mm3/N•m). Attributed to grain refinement and solution strengthening brought by N-doping, the resistance of the matrix to plastic deformation and delamination is enhanced effectively. Besides, the in-situ N-doping helps to reduce corrosion sites and promote the formation of protective films to improve electrochemical corrosion resistance. Therefore, in-situ N-doping is an effective method to improve the wear resistance and corrosion resistance of superalloy.

Regulating the mechanical properties of (μm B4C+nm SiC)/7075Al composites via nano-SiC content

In this study, micron B4Cp (m-B4Cp) and nanometer SiCp (n-SiCp) reinforced 7075Al composites were prepared by high-energy ball milling, hot press sintering, and hot extrusion. The microstructures and mechanical properties of composites were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), tensile testing, and synchrotron radiation computed microtomography (SR-μCT). The results showed that n-SiCp and m-B4Cp were uniformly distributed in the aluminum matrix without interfacial reaction. The optimal grain refinement was achieved by adding 1.5 wt% n-SiCp, improving the strength and ductility of composites. The room temperature yield strength (YS) and ultimate tensile strength (UTS) of M5N1.5 composites were increased from 350 MPa and 401 MPa of 7075Al to 460 MPa and 502 MPa, respectively. The results revealed that the YS and UTS of composites were decreased, but elongation was increased with increasing temperature. When the temperature increased to 200 °C, the elongation of 7075Al and M5N1.5 was increased from 5.9 % and 4.7 % to 8.7 % and 10.9 %, respectively. Quantitative analysis revealed that dislocation strengthening and grain refinement strengthening caused by the addition of n-SiCp are the dominating strengthening mechanisms at both room and high temperature, while the contribution of m-B4Cp to the strengthening of the composites is very small.

Excellent combination of strength and ductility in austenitic lightweight steel achieved by warm rolling process

In this study, warm rolling was applied to Fe–28Mn–11Al–1C–5Ni (wt.%) austenitic lightweight steel, which realized the higher dislocation density and finer dislocation-cell structures, achieving a better mechanical properties with ∼2.0 GPa of yield strength and ∼6.8 % of total elongation than cold rolling in the same conditions. In the subsequent partial recrystallization condition, the numerous dislocations and substructures existed in warm rolled steel provide more heterogeneous nucleation sites for grain refinement, resulting in the ultrafine-sized austenite and B2 with the size of 0.36 μm and 0.24 μm, respectively. Combined with grain refinement strengthening, solid solution strengthening, precipitation strengthening, and dislocation strengthening in the unrecrystallized austenite, the present steel shows an ultimate tensile strength of 1734 MPa, a uniform elongation of 21.7 % and a specific tensile strength of 267 MPa g−1 cm3. Such an excellent combination of strength and ductility induced by simple warm rolling and annealing is much better than previously reported for lightweight steels.

EBSD analysis and mechanical properties of low-carbon steel during drawing with shear deformation

In the current study, the effect of shear deformation combined with conventional drawing processes on the evolution of the microstructure, texture and mechanical properties of low-carbon steel was investigated using electron backscatter diffraction, Vickers microhardness and tensile test. For that, two samples were drawn with a shear die to 8 (ShD8–23 sample) and 23 % (ShD23–23 sample) of diameter reduction and followed by conventional drawing for a diameter reduction of 23 %, respectively. The results show that the overall grain size reduction was about 9.2 and 12.8 % and a significant increase in low-angle grain boundary fraction of 77.8 and 85.9 % for ShD8–23 and ShD23–23 samples, respectively. A typical <110>//DD fiber containing A {110}<001>, B {110}<111> and C {110}<110> components was formed in both samples. In contrast to the B and C components, the stored energy in the A component, estimated by the Kernel Average Misorientation (KAM) approach, was found to be low and stable with increasing deformation. The ultimate tensile strength of the ShD8–23 and ShD23–23 samples was improved by 49 and 52 %, respectively. The yield strength was increased by 95 and 108 % for ShD8–23 and ShD23–23 samples, respectively. The mechanical properties improvement was related to the deformation and initial microstructure. The contribution of dislocation strengthening, originated from geometrically necessary dislocations, is found to be dominant for the increase of yield strength rather than grain refinement strengthening.

A new investigation on graphene-reinforced 304L nanocomposite made by additive manufacturing process: Microstructure and tribology study

In this study, selective laser melting (SLM), as an additive manufacturing method, was applied to produce graphene/304L nanocomposites with various graphene particle sizes and contents. The effect of the graphene particle size (1 μm and 50 nm) and volume fraction on the microstructure behaviors, constitutional phases, mechanical performance, and wear characteristics of the SLM-processed nanocomposite specimens was studied. It was concluded that the reinforcing particle content and size play a remarkable impact on the densification features and the densification level improvs when the fine starting reinforcing particles are used, due to the development of the reinforcement–matrix wettability. In addition, the microstructure refinement and increased hardness values occurred in the SLM-processed nanocomposite system with the addition of reinforcing particles (both sizes). The wear examination indicated that the coefficient of friction (COF), wear rate, and mass loss decreased due to the reinforcement prominent effect, namely grain refinement and grain-boundary strengthening. According to surface topography analysis, the depth of the groove in the processed sample made by fine graphene reinforcement is lower than the other sample.

Oxide precipitation strengthening in Cu alloy modified with trace amounts of Nd during dynamic impact

In this study, three kinds of Cu-Nd alloys were prepared. The effect of Nd content on the dynamic impact behavior of the Cu-Nd alloys and its strengthening mechanism were studied. The results show that during the dynamic impact process, nano-scale oxide particles are precipitated in the alloy matrix, and a large number of cracks are formed along the grain boundaries, and the formation of shear bands and thermal grooves are also observed in local areas. With the increase of Nd content, the compressive strength of the alloys increases significantly, the grain size is refined, the number of twins increases, the grooves are much deeper and the number of the precipitated nano-oxide particles also increase significantly. In addition, due to the refinement of the grain size, the crack length is reduced. The increase of the alloy strength is mainly attributed to the nano-scale oxide precipitation strengthening and grain refinement strengthening.

Study of the Effects on the Strengthening Mechanism and Wear Behavior of Wear-Resistant Steel of Temperature Controlling in Heat Treatment.

To improve the wear resistance of the materials used for blades in engineering machinery, this study focused on the microstructural characteristics, mechanical properties, and wear behavior of HB500 grade wear-resistant steel developed using an optimized heat treatment system. To improve the temperature uniformity of the heat treatment furnace, the method of cyclic heating was used to heat the components. Carefully designing the quenching equipment, such as using a cross-shaped press, was employed to enhance the quenching effect and reduce the deformation of the steel plates. The crystal orientation analysis revealed a uniform and fine-grained microstructure, primarily characterized by plate-type tempered martensite, which indicated a good hardenability. The microstructure observations showed that the width of martensite is approximately 200 nm, with a significant presence of dislocations and carbides. Tensile tests and multi-temperature gradient impact tests indicated superior mechanical properties compared to similar grade wear-resistant steels, including a Rockwell hardness of 53, tensile strength of 1610 MPa, yield strength of 1404 MPa, and total elongation around 12.7%. The results of friction and wear experiments indicate that the wear rate decreases as the load increases from 100 N to 300 N, demonstrating an excellent wear resistance under a large load. Observations of the worn surfaces indicated that the wear mainly involved adhesive wear, fatigue wear, and oxidative wear. The properties' improvements were attributed to microstructure refinement and precipitation strengthening. This study indicates that designing a heat treatment system to control temperature uniformity and stability is feasible.

Microalloying design in directed energy deposition of complex-concentrated alloy: Pre-nitriding to inhibit hot cracking and promote mechanical properties

With the development of ultra-supercritical (USC) power generation technology, the increase of steam temperature puts higher requirements for high-temperature performance and processing reliability of superalloys. Here, a new complex-concentrated alloy (CCA) is developed for manufacturing the devices in USC circumstances. For the laser additive manufacturing of CCA, avoiding the hot cracking is crucial to guarantee reliable printability and favorable service performance. In this work, the nitrogen (N) is introduced innovatively by pre-nitriding powder to ensure sufficient N to combine with the matrix during the directed energy deposition process. The solidification temperature range can be narrowed to inhibit the hot cracking with the N-doping effectively. As a result, the sample with N-doping exhibited an extraordinary performance of strength (1083.51 MPa) and plasticity (20.83 %). The strengthening mechanisms mainly include solid solution strengthening, grain refinement strengthening, and dislocation strengthening. The elimination of defects leads to an increase in ductility in the meantime. In addition, the dynamic oscillation of the molten pool caused by pre-nitriding powder also has a nonnegligible impact on the breakdown of grain epitaxy growth and the initiation of grain refinement. These findings shed new light on the alloy design concept to inhibit hot cracking and promote mechanical properties.

Structural-functional integrated TiBw/Ti–V–Al lightweight shape memory alloy composites

Driven by the increasing demands in advanced aerospace engineering, the integrated structural and functional materials are explored. In present study, we fabricate the TiBw/Ti–V–Al lightweight shape memory alloy composites with large recoverable strain (>5 %), high specific strength (>200 MPa cm3/g) and good elongation (>20 %). The satisfied structural and functional performances are attributed to the unique gradient microstructure, including TiB whiskers, short-range martensitic nanodomains and long-range martensitic microdomains. TiBw with the optimized orientation exhibits high load-bearing capacity. The transition area between TiBw and matrix is composed of short-range martensitic nanodomains. Nanodomains are affected by the diffused interstitial B atoms and local internal stress field regulated by TiBw. The elastic interaction energy between nanodomains and TiBw are calculated according to the Eshelby method. Upon deformation, nanodomains grow to long-range martensitic laths. The long-range martensitic laths keep stable after unloading. The microstructure evolution ties well with the Landau free energy model. It achieves effective loading transfer from matrix to reinforcement phase, resulting in less irreversible defects and better shape memory effect. In addition, grain refinement strengthening, loading transfer strengthening and solution strengthening are utilized to achieve the improvement of the strength and plasticity. The finding offers a promising inspiration for the development of new type shape memory alloy composites with integrated structural and functional properties.

Microstructure characterization and age hardening response of Mg-8Sn-2Al alloy with Bi, Ag addition

The effects of Bi and Ag addition on the microstructure and age hardening response of Mg-8Sn-2Al alloy were investigated in this study. The Mg2Sn phase distributed along grain boundaries was observed in as-cast Mg-8Sn-2Al alloys and disappeared after solution treatment due to the Sn dissolution into ɑ-Mg matrix. However, a majority of Mg2Sn phase disappeared and few Mg2Sn particles still existed in the solid solutioned Mg-8Sn-2Al alloys containing Bi element. Mg2Sn precipitates formed in all peak-aged alloys. And Al, Bi and Ag elements are enriched in the areas of lath-shaped and spherical Mg2Sn precipitates in peak-aged Mg-8Sn-2Al-1.5Bi-1Ag alloy. Bi and Ag elements can act as heterogeneous nucleation sites and restrict the growth of precipitates to improve the age hardening response of Mg-8Sn-2Al alloy. Meanwhile, the undissolved Mg3Bi2 phase or early precipitated Mg3Bi2 phase during ageing treatment probably change the morphology and elements distribution of Mg2Sn precipitates. In addition, Ag and Bi atoms play a role on grain refinement and solution strengthening in Mg-8Sn-2Al alloy. Therefore, the micro-hardness value of peak-aged Mg-8Sn-2Al-1.5Bi-1Ag alloy increased to 69.9 HV from 47.4 HV of solid solutioned Mg-8Sn-2Al alloy. The precipitation behaviour, refined second phase, grain refinement and solute atoms synergistically made contributions to the strength improvement. The roles of Bi and Ag elements on improving age hardening response and precipitates characteristics are discussed in this study, which provides an important reference for exploring aged Mg-Sn alloys.

Microstructure, mechanical properties and multiphase synergistic strengthening mechanisms of LPBF fabricated AlZnMgZr alloy with high Zn content

In this work, a novel aluminum alloy with high Zn content was designed for laser powder bed fusion (LPBF) forming process. Aluminum alloy powder containing 14 wt% Zn and 2 wt% Zr was produced to conduct LPBF experiments with different process parameters. The analysis of the specimens revealed that the up facing surface exhibited an average microhardness peak value of 170.6 HV, achieving the ultimate tensile strength (UTS) of 573 MPa and the elongation of 11.6 %. There was no significant change in grain size and a large amount of plate-like η' (a metastable precipitate MgZn2 phase) phase precipitated within the grains after aging treatment (120°C, 21 h). The specimen reached the average microhardness peak of 181.7 HV and the UTS of 605 MPa. The principal strengthening mechanisms in the LPBF-formed samples were solid solution strengthening and grain refinement strengthening. After aging treatment, the precipitation of the second phase from solute atoms led to grain refinement strengthening and second-phase strengthening becoming the predominant factors to enhance the sample's strength. Al14ZnMgZr alloy have great application prospect in high strength and tough service environment.

Synergistic enhancement the strength and ductility of crossover Al–Cu–Zn–Mg alloys via Zr(Sc or/and Hf) microalloying to create heterogeneous lamellar structure

A crossover Al–Cu–Zn–Mg alloy with a heterogeneous lamellar structure (HLS) was obtained by microalloying Zr(Sc or/and Hf) to form a multiscale second phase, and the microstructure and mechanical properties of the alloy were investigated. The Sc-containing alloys produce a large number of micron and submicron W phase particles and nano-sized Al3(Sc,Zr)/Al3(Sc,Hf,Zr) dispersions with core-shell structures. The Hf-containing alloys have a micron-sized second phase particles and nano-sized Al3(Hf,Zr) dispersions. The multiscale second phase formed by microalloying of Sc or/and Hf promotes recrystallization via particle-stimulated nucleation (PSN), whereas the nanoscale Al3M dispersions pinning sub-structures to inhibit grain growth, and these two mechanisms influence the recrystallization process to form a heterogeneous lamellar structure. The microalloying produces a large number of Al3M dispersions and the refinement grain by hindering recrystallization, which enhances the strength through precipitates strengthening and grain refinement strengthening. The Hf added alloy with typical HLS microstructure improve the ductility of the alloys due to the delamination toughening effect and the avoidance of the formation of coarse brittle phases.