Soft Orientation Research Articles

Deformation behavior of Gd alloyed CoCrFeNi high entropy alloy at high temperature under the influence of local nano-ordered structure and misorientation

The thermomechanical processing (TMP), which is an industrial process that includes deformation and heat treatment, represents a novel approach to enhancing the mechanical properties of metallic materials. However, it requires extensive research on the high-temperature deformation behavior of alloys during its application process. The present study conducts hot compression tests at 700 °C and 800 °C, as well as detailed microstructural characterization of the deformed material after hot deformation, to comprehensively discuss the mechanical properties and deformation behavior at high temperature of the (CoCrFeNi)100-xGdx (x = 0, 0.5, 1, 2, 3 at.%) HEAs. The (CoCrFeNi)100-xGdx HEAs exhibit an excellent combination of strength and plasticity in high temperature. The original dendritic microstructure in the (CoCrFeNi)100-xGdx HEAs was completely fractured and transformed into a mass of deformed structures during thermal deformation. The mechanical properties at high temperature of the alloy system originate from the misorientation in the microstructure. Dislocation slip is the main deformation mechanism of the alloy system at high temperature. The coordinated deformation of the soft orientation for FCC phase and the hard orientation for HS phase affects the dislocation morphology in the microstructure. Dynamic recovery (DRV) plays a dominant role in the flow behavior of the alloy at high temperature, and work hardening is the main strengthening mechanism during plastic deformation. The correlation between microstructure evolution and mechanical properties of Gd alloyed CoCrFeNi HEAs during hot deformation has been established through comprehensive studies on deformation behavior.

Microstructure evolution and springback behavior in single-pass roll bending of magnesium alloy plates

Using magnesium alloy plates instead of high-strength steel and titanium alloys in roll-formed parts significantly improves the lightweight, damping, and heat dissipation properties of automotive components. This paper employs finite element simulation combined with experimental methods to perform single-pass roll bending of AZ31B magnesium alloy plates at angles of 0°-15°, 0°-25°, and 0°-35°. Measured the springback angle and microhardness at the bends, and used optical microscopy (OM) and electron back scatter diffraction (EBSD) to analyze the microstructural characteristics, texture, and orientation evolution at the bend during the roll bending process. The results indicate that during roll bending, the inner bend area has significantly more twins than the outer area, with more pronounced grain refinement on the inner side. {10−12} tensile twins mainly coordinate plastic deformation, with some {10−12}-{10−12} tensile twin variants present. The inner bend area's texture shifts from ND to TD direction, strengthening the TD direction texture, while the outer area retains typical rolling texture. The prismatic slip in the inner region of the bend changes from hard to soft orientation. The inner region is mainly coordinated plastic deformation by prismatic slip, while the outer region is mainly coordinated by basal slip. As single-pass roll bending angles increase, the increase in twin boundaries and low-angle grain boundaries (LAGBs) significantly reduces the springback angle. Additionally, grain refinement and increased geometric necessary dislocation density lead to higher microhardness.

Sheet-based friction stir additive manufactured 6061 aluminium alloy: Microstructure, texture evolution and mechanical properties

A 6061 Al alloy build consisting of 3 additive layers was successfully fabricated using a sheet-based friction stir additive manufacturing process. The study focused on analyzing the microstructure and texture characteristics in the central regions of each layer and the thermal mechanical affected zones (TMAZs) beneath the stir zones (SZs). Mechanical properties of the final multilayered build were also analyzed. The results revealed that, following plastic deformations and thermal cycles, the equiaxed grains formed in the central region of layer 2 were the finest (∼7.9 μm) among the three layers, attributed to the highest degree of recrystallization. Additionally, the average grain size of the TMAZs further decreased to ∼4.0 μm due to lower frictional heat generated by the tool pin. Furthermore, the geometrically necessary dislocation densities of the TMAZs showed a slight increase compared to those of the central regions. In terms of textures, shear and deformation textures were predominant in the central regions, while shear texture dominated the TMAZs. The primary precipitates found at the center of the SZs included β, β′, Q′, Al8Fe2Si and (Fe,Mn,Cr)3SiAl12. Besides, the yield strength and ultimate tensile strength of the build drop significantly to 119.7 MPa and 204.6 MPa, respectively. Moreover, a non-monotonic decrease in hardness as the increase of distance from the top of build could be found, due to the existence of numerous grains with soft orientations and the intense dissolution and coarsening of β” and β’ phases.

Microstructure and mechanical properties of a low-alloyed Mg–Zn–Al–Ca alloy: Effect of extrusion speed

A low-alloyed Mg-1.2Zn-0.6Al-0.1Ca (wt.%) alloy was extruded at 200 °C with different ram speeds (0.5–4.0 mm/s), and the microstructure and mechanical properties were studied systematically. Heterostructures with fine dynamic recrystallized (DRXed) grains and coarse unDRXed grains were achieved at lower ram speeds of 0.5 mm/s and 1.0 mm/s, and fully-DRXed microstructure was attained at 4.0 mm/s. Increasing the extrusion speed resulted in an increase in DRXed grain size from 0.9 μm to 3.8 μm, and a transformation of the DRXed texture component from <10 to 10>−<11–20> to a new orientation that deviated by approximately 14°. The sample extruded at 0.5 mm/s presented an excellent tensile yield strength (TYS) of 369 MPa along with a 7.8% elongation, which was mainly due to the high hetero-deformation induced (HDI) strengthening provided by its heterostructures. Increasing ram speed resulted in an improved elongation despite a decreased TYS. The reasons for the decreased strength with increasing extrusion speed were mainly associated with grain growth, reduced dislocation density and weakened HDI strengthening. The reasons for the improved ductility with increasing extrusion speed were largely due to the increased DRXed grains fraction with soft orientations.

Failure analysis of 12Cr1MoVG outlet header for the reheater of the boiler under high temperature and high-pressure environment

ABSTRACT After operating for 11,640 h, a boiler failed due to multiple cracks generated in the inner wall of the outlet header for the reheater. A thorough analysis was conducted in this work, including evidence and specimen collection, chemical composition analysis, tensile and impact test analysis, metallographic analysis, energy dispersive spectroscopy (EDS) analysis, and electron backscattering diffraction (EBSD) characterisation, to reveal the causes of cracks in the outlet header of the reheater. The tensile strength-Rm and the average micro-Vickers hardness of the outlet header is 496 MPa and 168 HV, respectively. Besides, the microstructure was found to meet the requirements of the relevant standards. The grains near the crack exhibited different degrees of deformation, and the deformation degree increased with the decreasing distance from the crack. In addition, the grains with the Schmid factor value greater than 0.3 accounted for 99.8% near the crack, indicating that the grains surrounding the crack were predominantly soft orientation grains. Thus, many deformation bands mainly composed of low-angle boundaries were induced inside the grains near the crack. Eventually, it was concluded that alkali stress corrosion and thermal fatigue resulted in the failure of the outlet header.

The Role of Deformation and Microstructure Evolution on Texture Formation of a TA15 Alloy Subjected to Plane Strain Compression.

In this study, the texture formation mechanism of a TA15 titanium alloy under different plane strain compression conditions was investigated by analyzing the slipping, dynamic recrystallization (DRX) and phase transformation behaviors. The results indicated that the basal texture component basically appears under all conditions, since the dominant basal slip makes the C-axis of the α grain rotate to the normal direction (ND, i.e., compression direction), but it has a different degree of deflection. With an increase in deformation amount, temperature or strain rate, {0001} poles first approach the ND and then deviate from it. Such deviation is mainly caused by a change in slip behaviors and phase transformation. At a smaller deformation amount and higher strain rate, inhomogeneous deformation easily causes a basal slip preferentially arising from the grain with a soft orientation, resulting in a weak basal texture component. A greater deformation amount can increase the principal strain ratio, thereby promoting other slip systems to be activated, and a lower temperature can increase the critical shear stress of the basal slip, further causing a dispersive orientation under these conditions. At a higher temperature and a lower strain rate, apparent phase transformation will induce the occurrence of lamellar α whose orientation obeys the Burgers orientation of the β phase, thereby disturbing and weakening the deformation texture. As for DRX, continuous-type (CDRX) is most common under most conditions, whereas CDRX grains have a similar orientation to deformed grains, so DRX has little effect on overall texture. Moreover, the microhardness of samples is basically inversely proportional to the grain size, and it can be significantly improved as lamellar α occurs. In addition, deformed samples with a weaker texture present a higher microhardness due to the smaller Schmidt factors of the activated prism slip at ambient loading.

Analysis of compression response and coordinated deformation mechanism of bi-crystal Al-Cu-Mg-Ag alloy using CPFEM

In this paper, the compression behavior of Al-Cu-Mg-Ag bi-crystal samples at room temperature under different orientation combinations was studied. The stress-strain distribution of bi-crystal samples during the compression process was studied based on the crystal plastic finite element method (CPFEM). The deformation mismatch and slip transfer caused by the orientation combination of bi-crystal are discussed. The results show that the Al-Cu-Mg-Ag alloy bi-crystal samples with different orientations exhibit an anisotropic hardening response under compression. The combination of soft and hard orientation can coordinate the dislocation drive of the yield point, delay the elastoplastic transition of the yield point, and greatly improve the strength of the alloy. The mechanism of high strength of heterogeneous structure is proposed in this paper, which provides an important reference for the design of high strength heat resistant aluminum alloy for automobiles.

Enhanced plastic deformation ability of copper matrix composites through synergistic strengthening of nano-Al2O3 and Cr particles

The commercial application of Al2O3/Cu composites (ODS copper) with high Al2O3 content is consistently restricted by their plastic deformability. In order to synergistically improve the plastic deformability of Al2O3/Cu composites, Al2O3/Cu–Cr composites with different Cr contents are prepared by internal oxidation combined with heat treatment by replacing part of the Al2O3 particles with Cr phases heat treatment. The effects of Cr content on the microstructure and plastic deformability of Al2O3/Cu–Cr composites are investigated. It is found that the nano-Al2O3 (8 nm) and Cr (25 nm) particles are uniformly distributed in the copper matrix, and both reach a semi-congruent interface with copper matrix. Meanwhile, the copper matrix undergoes a transition from a [111]Cu hard orientation to a [100]Cu soft orientation, and the increase in Cr content leads to a more pronounced degree of recrystallization in the Al2O3/Cu–Cr composites. The results of geometric phase analysis (GPA) show that the coordinated deformability between Cr and Cu is better than that between Al2O3 and Cu. The elongation of 2.5Al2O3/Cu-0.3Cr composite increased to 24.48 % from 22.47 % of the Cr-free 2.8Al2O3/Cu composite. The results of tensile strength calculations show that the tensile strength of Al2O3/Cu–Cr composites is mainly dominated by matrix strengthening and Orowan strengthening induced by Al2O3 particles, while grain strengthening, dislocation strengthening, and Orowan strengthening induced by Cr particles play a secondary role. The correlation coefficient (R2) is 0.95 after fitting the experimental and theoretical values of tensile strength of Al2O3/Cu–Cr composites.

High‐Cycle‐Fatigue Anisotropy of an Aluminum Alloy Superthick Plate

The effect of anisotropy on high‐cycle fatigue (HCF) property along the rolling direction (RD) and the transverse direction (TD) of a 7××× aluminum alloy super thick plate is mainly investigated in this study. The results show a similar microstructure at different thicknesses, and the HCF properties are close as well. The fatigue fracture morphologies show that the fatigue crack sources are all located on the surfaces of the RD and TD specimens. By considering the differences in the HCF properties, there is only a slight anisotropy effect at the center thickness of the plate, which can be attributed to the tensile anisotropy caused by textures. Besides, the fatigue damage degree along the TD is slightly higher than that along the RD at the center thickness. The reason can be explained by two aspects: one is the higher probability of defect occurrence along the TD compared with that along the RD which is analyzed by the previously proposed Yield strength‐Tensile strength‐Fatigue strength model, and the other is the influence of the textures. The combination of hard and soft orientations may cause fatigue damage localization easily in the soft‐oriented grains which accelerates the fatigue failure.

How heterogeneous microstructure determines mechanical behavior of laser powder bed fusion AlSi10Mg

Laser powder bed fusion AlSi10Mg exhibits hierarchical and heterogeneous microstructure, which leads to anisotropic mechanical properties. The present work systematically investigated strength, ductility and their correlations to heterogeneous microstructure along different loading directions. Two AlSi10Mg samples presenting distinct features of Al–Si cellular structures and melt pool borders were analyzed, using combined tensile tests and digital image correlation measurements at both macro and micro scales. In addition, crystal plasticity modeling and simulation were conducted to reveal the deformation behavior and propensity to damage in the melt pool interiors and at the melt pool borders. Strain localizations are found in both the building direction and the perpendicular direction, due to weaker melt pool border and soft grain orientation, respectively. With the experimental and numerical results, it is demonstrated that the strength anisotropy mainly originates from the elongated Al–Si cellular structure, while the melt pool border plays a secondary role. Moreover, the ductility and its anisotropy appear to be determined by combined effects of strain localization, propensity to damage and constraints to crack formation. The findings of the present work unveil clearly how hierarchical and heterogeneous microstructure renders the macroscopic mechanical properties of additively manufactured Al alloys in different loading directions.

New insights into ductility improvement of a nickel-based superalloy through grain boundary engineering

Grain boundary engineering (GBE) provides an effective approach for tailoring the properties of metallic materials by optimizing the grain boundary character distribution (GBCD). Using electron backscatter diffraction analysis and uniaxial tensile testing at room temperature, this study systematically investigated the impact of GBE-type thermomechanical processing (TMP) on the ductility of an Incoloy 925 nickel-based superalloy (Alloy 925). The results showed that at 5 % strain, increasing the annealing temperature results in larger twin-related domains through strain-induced boundary migration. The GBE-type TMP can significantly enhance the ductility of Alloy 925, namely, the elongation increases from 64.22 % to 95.86 % as the annealing temperature increases from 1050 °C to 1100 °C. The evolved GBCD introduces more coherent twin boundaries with lower average residual Burgers vectors, enabling efficient dislocation transmission. In addition, extensive twinning can widely generate some soft orientations and simultaneously reduce the average Taylor factor within the twin clusters, leading to easy dislocation activation during plastic deformation. The synergistic effect of the optimized grain boundary network and twin cluster anisotropy promotes uniform plastic flow and effective strain accommodation, thereby enhancing the ductility of Alloy 925. Overall, this work provides novel and valuable insights into ductility optimization through GBE in a nickel-based superalloy.

Deformation mechanism of metastable oriented grains in high-purity tantalum under different strain paths

High-purity tantalum is used as the sputtering target material for integrated circuits, requiring fine grains and random texture. Understanding different orientation deformation mechanisms, especially the metastable orientation (here {112} crystallographic orientations), is beneficial for controlling the structure of tantalum target materials. This paper employs EBSD and crystallographic calculations to regulate the grain deformation behavior by introducing a reverse strain at 135° clock rolling. The deformation behavior and dislocation density distribution of the metastable oriented grains under different strain paths are quantitatively analyzed. Results show that unidirectional rolling (UR) generates stress concentration, causing an uneven distribution of geometrically necessary dislocation density. The splitting behavior of {112} and {111} grains is promoted, and they have similar deformation behavior in UR process, while the deformation of {100} oriented grains is significantly suppressed. Furthermore, changing the strain path promotes the splitting of {100} grains, and makes the {112} change from the soft orientation to the hard orientation. This change makes it easier to start multi-slipping, resulting in a more uniform deformation. Additionally, crystallographic calculations show that Schmid factor is ineffective in explaining the strain localization problem in BCC metals. However, Schmid factor difference ratio makes it possible to analyze the distribution of dislocation density in local regions through the quantitative calculation of multi-slipping.

In-situ deformation inhomogeneity and damage evolution of mixed-grain structure with tempered sorbite/bainite in Fe–Cr–Mo–Mn steel

The inhomogeneous tempered sorbite/bainite (TS/B) with various morphologies and orientations play a significant role in deformation coordination and damage evolution. In this paper, the influence of distinct morphologies and orientations of the mixed-grain structure with TS/B on the deformation heterogeneity were extensively investigated by in-situ tensile testing. Furthermore, a multi-scale model of dislocation density-based crystal plasticity (CP) coupled with the phase field method (PFM) was developed to illustrate the damage nucleation and its evolution via the representative volume element (RVE) modelling. The results shows that mixed-grain structure with TS/B exhibits non-homogeneous deformation during the tensile process, and the coarse grains bear the main plastic deformation, resulting in cross-slip traces and the wrinkling phenomenon at the grain boundary and the interior of coarse grains. Furthermore, the activation of slip systems was determined through slip trace analysis, and the slip transfer behavior between adjacent microstructure was analyzed. According to the critical resolved shear stress (CRSS), the {123}<111> slip system was determined to be the most activated slip system during the in-situ deformation. Hard-orientated lath-shaped B (M1) is more prone to accumulate low angle grain boundaries (LAGBs) than hard-orientated TS (M2) and soft-orientated granular B (M3), resulting in higher orientation rotation degree and geometrically necessary dislocations (GNDs) density of M1 than M2 and M3. The M1 exhibits the nucleation of damage during the initial deformation stage. In addition, compared with the M2 and M3, the Schmid factor (SF) of M1 dominates the transformation from hard orientation to soft orientation and the higher value of damage factor (φ) of M1 results in the more activated slip systems and local damage at high strain levels. This study provides new insights into elucidate the effects of TS/B morphologies and orientations on deformation heterogeneity and damage evolution in large-scale forged spindles for offshore wind power.

In-situ EBSD study of the coordinated deformation behavior of 2205 duplex stainless steel fabricated via laser powder bed fusion during the tensile process

Duplex stainless steels (DSSs) produced via laser powder bed fusion (LPBF) exhibit excellent strength and plasticity compatibility. In this study, in-situ electron backscatter diffraction (EBSD) was employed to investigate the coordinated deformation behavior of 2205 DSSs fabricated by LPBF with heat treatment at 1050 °C for 1 h, including strain distribution behavior and mechanism of stress concentration release. The results indicate that the initial deformation of LPBF samples is primarily concentrated in the austenite phase. As the tension progresses, austenite gradually transitioned to hard orientation, and the strain in austenite can pass through the phase boundary into the ferrite grain. To coordinate the deformation, ferrite transitioned to soft orientation through rotation towards the slip systems of {110}<−111> and {1–21}<111>. The stress concentration in ferrite can be alleviated by forming dislocation walls and cells through planar and cross-slip dislocations. In contrast, the stress concentration in austenite can be released by stacking faults and deformation twins. Compared to the as-cast samples, the yield strength of LPBF samples is improved from 472 ± 13 to 641 ± 17 MPa due to fine grain strengthening and dislocation strengthening. This study offers guidance for further enhancing the strength and plasticity of materials prepared by LPBF.

Uniaxial deformation behaviors and mechanism of Ti–6Al–4V alloy with bi-oriented grains

It is of great importance to investigate the deformation and damage mechanisms of polycrystalline materials with soft crystal orientations, considering the soft grains are usually the fatigue crack initiation sites. In this study, a Ti–6Al–4V alloy fully consisted of <01 1‾ 0> and <1‾ 21‾ 0> α (soft) grains was prepared and its uniaxial deformation behavior was investigated. Interestingly, no significant asymmetry on the tension-compression yield strength was found in this alloy with bi-grain orientations, though mechanical asymmetry was generally found in the traditional Ti alloys with strong texture. After high temperature solution treatment, the preferred bi-orientations were retained and the asymmetry degree of yield strength did not change, showing an excellent stability in texture and mechanical performance. Deformation mechanisms during tension and compression were studied and discussed. This work provides a new understanding on the deformation and damage mechanisms in the grains with soft crystal orientations, and may guide the microstructural design of Ti alloy for pursuing high mechanical and fatigue performances in the future.

Asymmetric tension-compression mechanical behaviors of extruded Mg-4.58Zn-2.6Gd-0.18Zr alloy with double-peak fiber texture

To clarify asymmetric mechanical behaviors of the extruded Mg-4.58Zn-2.6Gd-0.18Zr alloy during room temperature tension and compression, the evolution of microstructure, texture and strain hardening rate were systematically investigated when loading along the extrusion direction (ED). The results found that the as-extruded alloy exhibited <101̅0>-<112̅0> double-peak fiber texture, leading to obvious tension compression yield asymmetry and compressive yield plateau. Fiber texture kept stable and only texture intensity gradually decreased with the increasing tensile strain, while fiber texture was exhausted due to the extension twinning and <0001> texture component was aggravated with the increasing compressive strain. Moreover, twinning parts within grains with <101̅0> fiber texture was re-oriented to the c-axis paralleling to the ED, and that in <112̅0> fiber texture deviated about 30° away from the ED. This soft orientation would be finally rotated to the <0001> paralleling to the ED under the action of basal <a> slip, explaining why the <0001> pole dispersed at first and then concentrated with the increasing compressive strain. Three stages of strain hardening rate were both observed for tensile and compressive tests, while increment of Stage II was only observed under compression. Stage II in compression could be further divided into two parts with different slopes. Such phenomenon was seldom reported in Mg alloys, which was caused by different propagation and re-orientation of extension twinning in double-peak fiber texture, and weakened the effect of twin lamella segmentation with the increasing compressive strain. Findings in this work given us a better understanding of asymmetric tensile-compressive mechanical behaviors of extruded Mg alloys with double-peak fiber texture.

An insight into mechanical response and twinning behavior of bimodal textured AZ31 magnesium alloy under quasi-static and high strain rate compression

In this work, the dynamic, quasi-static response and twinning behavior of bimodal textured Mg–3Al–1Zn alloy is comparatively investigated at room temperature. The relationship between yield stress and bimodal texture is quantified and characterized as an increase of the yield stress with the increasing of the percentage of <0002>⊥ED (extrusion direction) component; the ultimate strength under high strain rate (103 s−1) was quite higher than that under quasi-static condition (10−3 s−1); but, the yield stress was just the reverse. The competition between twin nucleation and growth is significantly affected by a coupled effect of strain rate and texture. Twin nucleation shows positive strain rate sensitivity and is largely enhanced by dynamic deformation. However, the twin growth tendency is bimodal texture and strain rate dependent: it is favorable under quasi-static condition for samples with more soft orientations, while for samples with more hard orientations, dynamic deformation promotes twin growth. It is also found that a higher strain rate can stimulate the activation of more twin variant types in bimodal textured magnesium alloys.

Texture evolution of refill friction stir spot welding in alclad 2A12-T42 aluminum alloy

Electron backscatter diffraction (EBSD) was used to investigate the microstructure and texture evolution of 2A12-T42 aluminum alloy during refill friction stir spot welding (refill FSSW). The stir zone (SZ) and the thermo-mechanically affected zone (TMAZ) occurred dynamic recrystallization (DRX), with typical shear texture components. The texture is dominated by B component in the SZ, and dominated by A∗ and B components in the TMAZ. As the occurrence of the DRX, the storage energy of the grains gradually decreases, and there is a tendency to form lower energy grain orientations and texture weakening. The welding parameters determine the composition of the texture in different regions by influencing the degree of recrystallization. In the test group with the highest degree of crystallization, the SZ and TMAZ are dominated almost entirely by the B component. The TMAZ has more grains with soft orientation due to the difference in shear pattern and degree of recrystallization, which makes the texture reduce the mechanical properties of the joints. However, this reduction is not significant, with <10% variation for different test groups and regions. Compared to other strengthening mechanisms, the effect of texture strengthening is limited.

Effect of micro-texture and orientation incompatibility on the mechanical properties of Ti60 alloy

In this work, the effects of no-micro-texture regions (no-MTR, weak texture) and strong-MTR on the mechanical properties of Ti60 alloy engine blisk materials were investigated. It has been shown that MTR has a small effect on the room temperature strength of the alloy, but strongly affects plasticity, which reaches 18.5% for no-MTR alloy is twice as high as for MTR alloy. In contrast to no-MTR alloys, MTR alloys have only two-stage strain hardening behavior and fracture before meeting the instability criterion. Based on digital image correlation (DIC), high-resolution DIC and in-situ tensile analyses show that no-MTR alloys produce more uniform strains in deformation than MTR alloy. MTR exacerbates the slip deformation and local strain inhomogeneity in the hardening stage. Prevent premature fracture by eliminating MTR, thereby substantially increasing no-MTR alloy plasticity and triggering excellent work-hardening ability due to the uniformity of local deformation and dislocation multiplication. Meanwhile, the unique deformation characteristics of the combination of (0001) and (10 1‾ 0) soft orientations are proposed and elucidated. The incompatibility of the two orientations causes stronger slip deformation incompatibility, resulting in local strains and dislocation slips clustered mainly at the grain or MTR boundaries of the (0001) and (101‾ 0) soft orientation features, which further exacerbates the alloy failure at the microscopic level.

Investigation on the fatigue behavior of 7075 aluminum alloy at different aging states

To study the effect of the aging state on the low-cycle fatigue (LCF) performance of 7075 Al alloy, LCF experiments with different strain amplitudes (Δε/2 = 0.5%- Δε/2 = 0.9%) were conducted for underaged (UA), peak-aging (PA) and overaged (OA) states with similar tensile properties in this work. The effect of the aging state on the cyclic stress response behavior and the LCF lives of 7075 Al alloy was revealed by observing the dislocation configuration after LCF. The microcrack orientation on the surface of LCF samples was observed by the electron backscatter diffraction (EBSD) technique, and the results showed that the soft orientation inside the coarse grains was the main cause of fatigue cracking. Combined with the previous studies, we summarized the dominant factors for the LCF and high-cycle fatigue (HCF) properties of 7075 Al alloys at different aging states, i.e., the LCF properties were determined by tensile properties, while the HCF properties were dominated by dislocation slip mode.