7N01 Aluminum Alloy Research Articles

Comparative study of linear and nonlinear ultrasound applied to the detection of hydrogen damage in 7N01 aluminum alloy

7N01 aluminum alloy samples with different hydrogen damage degrees were prepared by electrochemical hydrogen charging technology. 7N01 aluminum alloy samples with different degrees of hydrogen damage were characterized by metallographic observation, hardness test and XRD test. The results show that the hydrogen content increases with the increase of hydrogen charging time. The surface of aluminum alloy is exfoliated and pits appear. The more severe the hydrogen damage, the greater the depth of pits. The microhardness of the 7N01 aluminum alloy decreases after hydrogen damage, which only occurs near the surface. After electrochemical hydrogen charging, AlH3 appears in the structure of 7N01 aluminum alloy, which is the result of increased hydrogen concentration. The ultrasonic echo signals of hydrogen damaged samples were obtained by a high frequency longitudinal probe ultrasonic detection device, and the results of linear and nonlinear ultrasonic detection were compared. Traditional linear ultrasonic detection parameters such as sound velocity and attenuation coefficient do not change significantly in the early stage of hydrogen damage, but increase significantly in the late stage of hydrogen damage. Due to the change of microstructure, the nonlinear coefficient increases approximately linearly in the early stage of hydrogen damage and decreases in the late stage of hydrogen damage. This study demonstrates the potential for combining linear and nonlinear ultrasonic measurements in hydrogen environment to more comprehensively study hydrogen damage.

Effect of aging process on precipitated phase and properties of mechanical extruded aluminum alloy

As the industrial sector develops, the performance requirements for aluminum alloys are also constantly improving. The study explores how aging and rolling treatment affect aluminum alloys' precipitates and mechanical properties by controlling the parameters of aging process and rolling deformation variables. 7N01 aluminum alloy was selected as the experimental object, and the samples were treated with non-aging, natural aging, artificial aging, and rolling deformation. How aging processes and rolling deforming affected alloys’ mechanical properties was evaluated through performance testing (mechanical and tensile testing) and material fiber characterization methods (advanced electronic instruments). These results confirmed that the combination of three aging pre-treatments + R20 % + 120 °C re-aging could significantly improve the hardness of aluminum alloys and maintain high ductility. As the deformation decreased, the time for the sample to reach the hardness peak was shorter and the hardness was higher. The 20 % deformation sample’s strength was better than the 80 % deformation sample’s. This confirmed that appropriate aging process and deformation combinations could improve the strength and hardness of aluminum alloys. These results have certain guiding significance for optimizing the aging process of mechanical extruded aluminum alloys and provide reference for the study of related alloy properties.

Enhanced corrosion resistance of ammonium heptamolybdate (AHM) sealed Li[sbnd]Al LDHs conversion coating on aluminum alloy

In this study, we prepared a hierarchical structured coating via a versatile two-step approach for the protection of 6N01 aluminum alloy. On the basis of as-prepared secondary alkane sulphonate (SAS) modified LiAl LDHs conversion coating (SLDH) by in-situ synthesis method, ammonium heptamolybdate (AHM) was introduced in the post-treatment to fabricate AHM@SLDH with enhanced corrosion resistance. The surface morphology, chemical composition and corrosion performance are characterized by means of scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS), etc. The hybrid coating has a persistence corrosion resistance in 3.5 wt% NaCl aqueous solution with protective efficiency of 99.64 %. As a highlight, a self-repairing function is detected in the immersion test, which is attributed to the weak oxidation function of Mo (VI). We believe that AHM@SLDH in-situ grown on aluminum substrate can provide a promising route for its corrosion prevention.

Research on the Microstructure and Mechanical Properties of Repaired 7N01 Aluminum Alloy by Laser-Directed Energy Deposition with Sc Modified Al-Zn-Mg

Aluminum alloy is an important material used in railway train structures. It is of great significance to repair aluminum alloy through directional energy deposition to reduce cost and improve the performance of the aluminum alloy. In this study, 7N01 aluminum alloy was repaired by means of laser-directed energy deposition (DED) with the powder of Sc-modified Al-Zn-Mg aluminum alloy as raw material. The microstructure and mechanical properties of the repaired specimens were studied through the metallographic microscope, scanning electron microscope, electron backscatter diffraction, universal tensile test, and Vickers hardness test in combination. The results show that the bonding interface of the repaired aluminum alloy is satisfactory, and the porosity is 2.8%. The grains in the repaired area are the columnar crystals growing vertically along the boundary of the melt pool with an obvious temperature gradient. Fine equiaxed crystals are distributed along the boundary of the melt pool, and Al3(Sc,Zr) particles play a role in grain refinement. The average grain size of the fine grain area in the repair zone next to the fusion zone is 9.1 μm, and the average grain size of the coarse grain area is 20 μm. The average tensile strength in the area of repair approaches 349 MPa, which is 91% that of the base material, and the elongation rate is 10.9%, which is 53.2% that of the base material. The hardness ranges between 122 HV and 131 HV, which is comparable to the base material. However, there is a significant decrease in the tensile strength and hardness of the base material (heat-affected zone).

Effects of in-situ ZrB2 nanoparticles and scandium on microstructure and mechanical property of 7N01 aluminum alloy

In this study, the in-situ synthesized ZrB2 nanoparticles and rare earth Sc were introduced to enhance the strength and ductility of 7N01 aluminum alloy, via the generation of high-melting and uniform nanodispersoids. The microstructure and mechanical property evolution of the prepared composites and the interaction between ZrB2 and Sc were studied in detail. The microstructure investigation shows that the introduction of rare earth scandium (Sc) can promote the distribution of ZrB2 nanoparticles, by improving their wettability to the Al melt. Meanwhile, the addition of rare earth Sc also modifies the coarse AlZnMgMnFe precipitated phases, refines the matrix grains and generates high-melting Al3(Sc, Zr)/Al3Sc nanodispersoids. Tensile tests of the composites show that with the combinatorial introduction of ZrB2 and Sc, the strength and ductility of the composites are improved simultaneously compared with the corresponding 7N01 alloy, ZrB2/7N01 composite and Sc/7N01 alloy. And the optimum contents of ZrB2 and Sc are 3 wt% and 0.2 wt% in this study. The yield strength, ultimate strength and elongation of (3 wt% ZrB2+0.2 wt% Sc)/7N01 composite are 477 MPa, 506 MPa and 9.8%, increased about 18.1%, 12.2% and 38% compared to 7N01 alloy. Furthermore, the cooperation strengthening mechanisms of ZrB2 and Sc are also discussed.

Comprehensive fatigue assessment for different types of aluminum fillet welded joints by local approaches

This paper investigates different types of MIG-welded fillet joints (lap welded joints, T welded joints, non-load-carrying cruciform welded joints, load-carrying cruciform welded joints) of 7N01 aluminum alloys under fully reversed pulsating axial loading. Fatigue assessments of the as-welded test results based on nominal, and local approaches are performed considering geometrical factors in different types of welded joints. The fatigue strength for these joints was compared with the international standard codes and those of other materials. Subsequently, the geometric parameters on the fatigue characteristic indicators in different types of welded joints were studied systematically by combining finite element calculated results and analytical methods, such as weld length, notch angles, incomplete penetration length, et al. The results show that the 7N01 lap welded joint owns the lowest fatigue strength (29 MPa) at 2*106 cycles. The corresponding geometrical analytical solutions of local fatigue indicator Strain Energy Density (SED) were established for these welded joints, which could quantitatively describe the fatigue characteristic relationships among different types of welded joints. The theoretical predictions based on SED notch geometric semi-analytical models are relatively higher than the recommended design curves of other local approaches.

Effect of extrusion process on the stress corrosion cracking resistance of 7N01 aluminum alloy

In this work, the effect of extrusion process on the mechanical properties and the stress corrosion cracking (SCC) resistance of 7N01 aluminum alloys were systematically investigated by tensile testing, slow strain rate testing (SSRT), electrochemical experiment, scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), and transmission electron microscope (TEM) observation, respectively. The results showed that with the increase of extrusion temperature, the SCC resistances of the alloys deteriorated, and this tendency was also proved by the electrochemical experiments including polarization curves and EIS results. The Microstructure observation results revealed that recrystallization played an important role on the SCC resistances of the alloys: the new recrystallization grain boundaries with higher grain boundary energy and wider PFZ could magnify the difference of electrochemical property between grain boundary area and the grain interior, thus raising the stress corrosion crack sensitivity of the alloys.

Fatigue properties and crack growth behavior of 7N01 and 6N01 aluminum alloys

Abstract In this study, the fatigue properties, microstructure, and surface damage tolerance of the 6N01 profile, 7N01 profile, and 7N01 plate aluminum alloy were studied. The fatigue test results show that the fatigue limit of the 7N01 profile was the highest and the 7N01 plate was the lowest. More importantly, most fatigue specimens failed in the safe life area provided by the Kitagawa–Takahashi line diagram, which indicates that there is a “short-notch effect” in the fatigue behavior of the pre-cracked aluminum alloys. For the sake of safety, according to the Kitagawa–Takahashi line diagram corrected by the fatigue test results, the effective harmless notch sizes a 0,eff of 6N01 profile, 7N01 profile, 7N01 plate is 23.92, 10.81, 24.32 μm, respectively, and their effective fatigue notch propagation threshold Δk eff,th is 0.81, 0.39, 0.77 MPa m1/2, respectively. These corrected values reestablished the fatigue tolerance of the three materials and provided the critical data reference for the practical application. Combined with this study and the analysis of the literature, it can be concluded that the short-notch effect of the three materials should be related to the microstructure, crack closure mechanism, internal defects.

The Microstructure and Mechanical Properties of 5083, 6005A and 7N01 Aluminum Alloy Gas Metal Arc-Welded Joints for High-Speed Train: A Comparative Study

This study aimed to conduct a comparative study on the microstructure and mechanical performance of 5083, 6005A and 7N01 Al joints used in China Railway High-speed (CRH) trains. We connected 10 mm-thick plates by three-layer and three-pass gas metal arc welding (GMAW). The results indicated that 6005A and 7N01 Al joints were more sensitive to grain boundary liquation in the partially melted zone (PMZ) than 5083 Al joins. Besides, recrystallization was obtained in heat-affected zones (HAZ). The 5083 Al joints experienced the most severe recrystallization and the grain size changed from 6.32 (BM) to 32.44 (HAZ) μm duo to intracrystalline strain induced by cold-rolled processes. The 7N01 Al alloys experienced the lowest extent of recrystallization and the grain size increased from 5.32 (BM) to 22.31 (HAZ) μm. Furthermore, significant precipitate evolution in the HAZ was observed. Original thin β” precipitates dissolved in HAZ of 6005A Al joints and transformed to the softer β phase. However, less precipitation transition was examined in 5083 and 7N01 Al joints. The precipitates’ evolution produced a softening region in HAZ of 6005A joints where the hardness was only 55 HV. The microhardness profile of the other two Al joints was less affected. The tensile strength of 5083, 6005A, and 7N01 Al alloy joints reached 323, 206 and 361 MPa, respectively. The 5083 Al and 6005A Al joints failed at HAZ near the fusion line while 7N01 Al joints failed at the fusion zone owing to the high strength of the base metal. The liquation, coarse grains by recrystallization, and precipitate evolution all decreased local strength, resulting in the fracture at HAZ.

Research on Microstructure and Mechanical Properties of CMT and MIG Welded Joints of A6N01 Aluminum Alloy

Cold metal transition welding (CMT) and molten inert gas shielded welding (MIG) two welding processes were used to conduct butt welding tests on 2mm thick 6N01 aluminum alloy, and the microstructure and mechanical properties of the welded joints obtained by the two processes were tested.The results show that the welded joints of 6N01 aluminum alloy welded by CMT process have better appearance and less welding defects and welding spatter. The tensile strength of CMT welded joints is 213MPa and the elongation after fracture is 10.64%, which is slightly higher than that of MIG welded joints. The hardness distribution of CMT and MIG welded joints and the hardness values of each zone are basically the same. Compared with MIG welded joints, the grain structure of CMT welded joints and the equiaxed crystals on the side of the fusion zone near the base metal are smaller and more uniform.

Microstructure and mechanical properties of A7N01 aluminum alloy weld joints filled with ER5356 and ER5087 weld wires

The A7N01-T5 aluminum alloy plates with the thickness of 12 mm were welded with the ER5356 and ER5087 welding wires, respectively, by the method of Metal Inert Gas (MIG) welding. The mechanical properties and microstructures of the welded joints were investigated by micro-hardness measurement, tensile test, energy dispersive spectroscopy (EDS), electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM). The results showed that the tensile strength and elongation of 7N01/5087 welded joint (the 7N01 aluminum alloy plate welded with ER5087 wire) were greater than those of 7N01/5356 welded joint (the 7N01 aluminum alloy plate welded with ER5356 wires), respectively. The high strength and the good elongation of 7N01/5087 welded joint were mainly attributed to the microstructure refinement in the weld zone through adding Zr element to promote the nucleation of Al grains around the Al3Zr sites.

Discharge Characteristic of Micro-Arc Oxidation on Aluminum Alloy under the Changing Electrolyte Temperature

The electrolyte temperature has a great influence on the performance of the coating prepared by micro-arc oxidation (MAO). The behavior of MAO discharge in the changing electrolyte temperature has been investigated. Compared to constant electrolyte temperature in conventional MAO process, the process has different discharge characteristics under the changing electrolyte temperature. The amplitude of pulse voltage was detected to study the change of discharge characteristic under the constant-current control of MAO power supply. Three successive discharge stages were differentiated by the variable the pulse voltage versus process time. Since there were significant changes in the sound, the sound signals were acquired and the audio analysis was used to describe the changing of the MAO discharge at different stages. Optical emission spectroscopy (OES) was employed in situ to unveil how the micro-discharge changed with the temperature increasing. Scanning electron microscopy (SEM) was used to characterize the morphology of the coatings on 6N01 aluminum alloy prepared by normal process with the constant-temperature control of the MAO electrolyte and by the process under the changing electrolyte temperature. A mode of film growth and micro-discharge was given to describe the effects of the changing electrolyte temperature in the whole MAO process.

Fitting and prediction for fatigue crack propagation of 7N01 aluminum alloy after long-term service based on deep belief network

The prediction and improvement of the material strength and crack propagation life of the key structures in high-speed trains are effective toward ensuring their operational safety. However, the fatigue crack propagation (FCP) life of the materials cannot be accurately predicted in the actual engineering environment using the traditional method based on the Paris formula. Under long-term complex working conditions, nonlinear characteristics are observed in the steady-state propagation region of the fatigue crack of the material, which cannot be expressed by the theoretical Paris curve. Therefore, this study proposed a novel method of establishing a deep belief network (DBN) to fit the experimental data for the FCP of 7N01 aluminum alloy. Despite the existing studies, the proposed model was directly driven by the FCP experimental data and did not require artificial feature extraction. The results showed that the proposed method provided a generalization that effectively fitted the experimental data of the T4 and T5 aluminum alloy materials. Also, the predicted results for the fatigue crack growth life of the T4 and T5 7N01 aluminum alloys calculated by the DBN method increased by 6.15% and 20.61% than those obtained by the Paris method, respectively.

Surface roughness effect on fatigue strength of aluminum alloy using revised stress field intensity approach

The fatigue strength of a component is known to highly depend on its surface quality, and it is thus necessary to develop a reliable and appropriate mathematical model for fatigue strength assessment that consider the effect of surface roughness. In this paper, different underlying physical mechanisms of the roughness effect at different regions of specimens were studied by fatigue testing of 7N01 aluminum alloy. For a quantitative analysis of the surface roughness effect, a revised stress field intensity approach for a fatigue strength assessment of microsized notches was proposed as a theoretical support. In the new model, a new form of weight function was built to adapt the characteristics of microsized notches. In addition, the effect of the field radius was fundamentally weakened on solution of the stress field intensity and the difficulty of fatigue failure region definition in the traditional method was overcome correspondingly in the proposed model, which made the calculated field strength accurate and objective. Finally, to demonstrate the validity of the revised approach quantitatively, specimens with conventionally sized notches were subjected to stress field intensity calculations. The results showed that the revised approach has satisfactory accuracy compared with the other two traditional approaches from the perspective of quantitative analysis.

Stress corrosion behavior of friction stir welding joint of 7N01 aluminum alloy

The friction stir welding joint of 7N01 aluminum alloy has strong stress corrosion sensitivity due to the inhomogeneity of microstructure. In this paper, the stress corrosion behavior of 14 mm thick plate 7N01-T4 welding joint and base metal was investigated by means of electrochemical impedance spectroscopy, slow strain rate tensile test and electron back scattered diffraction. The results show that the charge transfer resistance of the welding joint is obviously lower than that of the base metal. The lowest impedance at the joint is 698 Ωcm2, but the lowest impedance is 1082 Ωcm2 at the base metal.The lowest Rct value at the weld is only 64.5% of the base metal. The thermal-mechanical affected zone on the rear side is the worst area of the resistance to stress corrosion. There are more deformed grains and larger Schmidt factor close to 0.5 in this area, and the different grain orientation can easily lead to the concentration of internal tensile stress and the formation of crack propagation.

Effect of Aging Treatment on the Corrosion Resistance Properties of 7N01 Extrusion Aluminum Alloy.

The influences of non-isothermal aging (the temperature range is 150–180 °C, and the heating rate is 5 and 20 °C/h alternately), single-peak aging (aging at 120 °C for 24 h, then water quenched was followed at room temperature), and two-stage aging (aging at 105 °C for 8 h first, then increasing aging temperature to 135 °C and keeping for 12 h, followed by water quenching at room temperature) on the corrosion resistance and microstructure of the 7N01 aluminum alloy under 3.5 wt.% NaCl were investigated using electric polarization curve test and exfoliation corrosion. After aging, the hardness of samples was measured by a Vickers micro-hardness tester, and the electrical conductivities were obtained using the eddy current method. The results show that the steady phase η and metastable phase η′ are precipitated in the grain boundary of 7N01 aluminum alloy after non-isothermal aging, and their distribution is discontinuous. The hardness of the alloy can reach 136.9 HV1 and the electrical conductivity can reach 35.8% IACS, which is close to the hardness of single-peak aging and the conductivity of two-stage aging, respectively. Compared with single-peak aging, the corrosion current density of non-isothermal aging is reduced by 15.5%, and that of two-stage aging is reduced by 28.9%.

Mechanical and Corrosion Properties of 7N01 Aluminum Alloy After Non-isothermal Heat Treatment under Different Quenching Conditions

Mechanical and Corrosion Properties of 7N01 Aluminum Alloy After Non-isothermal Heat Treatment under Different Quenching Conditions

Three‐Dimensional Stress Intensity Factor Correction Method Based on Thickness Size Effect

This paper presents the fatigue crack growth test of 7N01 aluminum alloy specimens with different thicknesses under three‐point bending. Moreover, the effect of specimen thickness on the fatigue crack growth life was analyzed. The influence mechanism of the thickness size effect on the stress intensity factor was explored. A three‐dimensional stress intensity factor calculation model based on the thickness size effect was proposed by combining the finite element method and the interaction integral method. The results show that the fatigue crack growth life of 7N01 aluminum alloy decreases with the increase of specimen thickness. The numerical solutions of the stress intensity factor (the proposed model) are higher than the analytical solutions (the traditional formula) in the steady‐state crack growth stage. The difference between numerical solutions and analytical solutions increases with the increase of crack growth length and specimen thickness. Compared with the analytical solutions, the relationship curve between crack length “a” and cycle number “N” from the numerical solutions is closer to the experimental data. This result proves that the proposed calculation model can correct the stress intensity factor with the thickness size effect.

Galvanic corrosion behavior of friction stir welded AZ31B magnesium alloy and 6N01 aluminum alloy dissimilar joints

The corrosion behavior and corrosion rate of friction stir welded AZ31B magnesium alloy and 6N01 aluminum alloy dissimilar joints were studied using real-time imaging, potentiodynamic polarization, EIS, and hydrogen evolution tests. The corrosion rate was found to increase, in order, Al base metal (BM-6N01) < Mg base metal (BM-AZ31B) < stirred zone. The galvanic coupling of the Mg phase to the other phases enhanced the corrosion of both BM-AZ31B and BM-6N01. Accompanying the intense corrosion at BM-AZ31B, water reduction on the cathodic particles of BM-6N01 elevated the interfacial pH to a level where the Al matrix corroded to AlO2−.

Mechanical Behavior and Microstructure of Hot Deformation of with Er 7N01 Aluminum Alloy

In this paper, an Al-Zn-Mg-Cu alloy with a small amount of Er and Zr added was used as the research object. The homogenization annealing was carried out, and the 7N01 aluminum alloy was used at 300 °C, 350 °C, 400 °C, 450 °C and 0.1 s-1, 1 s-1, 10 s-1 deformation conditions by Gleeble-3500 thermal simulator. Optical Microscopy (OM), Scanning Electron Microscopy (SEM), Electron Backscatter Diffraction (EBSD) and Transmission Electron Microscopy (TEM) were used for microstructure analysis. The results show that the stress-strain curve of with Er 7N01 aluminum alloy can be divided into micro-strain stage, uniform deformation stage and steady-state flow stage during the thermal compression process. The flow stress of 7N01 aluminum alloy achieved peaks at the initial stage of strain, and then increased with the increase of strain rate and the decrease of deformation temperature. With the increase of deformation temperature and the decrease of deformation rate, the recrystallization process was significantly increased.