Search

To solve the problem of poor formability of 7075-T6 aluminum alloy at room temperature and the degradation of properties after conventional warm forming, this paper put forward the contact heating warm forming (CHWF) process, which can make aluminum alloy blank reach the forming temperature in a very short time through the heated plates with pressure. Firstly, the uniaxial warm tensile tests with contact heating were carried out at 160–240 °C. Then the parameters of CHWF, namely forming temperature, contact pressure and holding time, were optimized based on the response surface and genetic algorithm. The U-shaped parts were obtained by using the optimal parameters. The results showed that the work hardening and dynamic recovery softening of 7075-T6 aluminum alloy at 200 °C could reach an equilibrium state, and the uniform plastic deformation ability was strong. The optimal parameters of CHWF were the forming temperature of 200 °C, the contact pressure of 10 MPa, and the holding time of 16 s. The U-shaped parts obtained by the optimal process had a small springback angle. Compared with the warm forming by using heating furnace, η′ precipitate did not grow significantly under CHWF condition and the hardness could reach 93% of T6 state. [ABSTRACT FROM AUTHOR]

The 7075-T6 aluminum (Al) alloy is a high-strength material with great application potential. However, the tensile strength and elongation of its arc-welded joints are severely reduced compared to the base metal (BM), with only 57.3% and 14.4% of the BM values, respectively. To improve both strength and plasticity simultaneously, a novel post-weld composite treatment process combining solution treatment, partial rolling, and natural aging treatment (SRA) was proposed. The SRA process enhanced the strength and elongation of welded joints to 84.5% and 83.1% of the BM, respectively. In different regions of the joints, the SRA process involved different strengthening mechanisms, including stronger work hardening in Region I, η′ phase precipitation and weaker work hardening in Region II, and refinement of the η’ and η phase in Region III. The SRA process also improved the formability of the welded joints from 62.5% to 87.5% of the BM. In addition, the SRA process increased the median fatigue life of welded joints by a factor of approximately 2–6. This was achieved by increasing the strength and microhardness of the fusion zone, which, in turn, reduced the number of fatigue crack sources and shifted crack sources from the surface to subsurface regions.

AbstractThe study predicts friction stir process (FSP) parameters using an artificial neural network (ANN) model. A design of experiment (DoE) approach is used to conduct experiments on FSP and to evaluate the best operating parameters of FSP. ANN uses 30 neurons, 1 hidden layer, and an input and output layer in the Matlab® environment. ANN predicts the output parameters with R values of 0.999, 0.995, and 0.992 for training, validation, and test datasets, respectively, while the overall R-value is 0.997. GRA is used to optimize and rank the parameters of the processes and revealed that the rotational tool speed should be 1180 rpm, traverse feed rate 38 mm/min, and tool tilt angle 1° for best results. The optimized values obtained are 380 MPa, 3.8 µm, 138 HV, and 14% for tensile strength, grain size, microhardness, and elongation, respectively. According to the analysis of variance (ANOVA) and grey relational analysis, the order of influencing parameters on output factors was rotational speed (80%), followed by transverse feed (19%) and tool tilt angle (1%). An ANN is further used to predict using the two most significant parameters—rotational speed and traverse feed. The modified ANN has nearly the same R values as the original ANN. Thus modified ANN may be used for prediction.

This work aims to explore the effect of cutting parameters on the cutting force, surface quality, and corrosion resistance of 7075‐T6 aluminum alloy after and without cryogenic treatment. Cryogenically treated (T6‐C) and noncryogenically treated (T6) 7075‐T6 aluminum alloy samples are experimentally cut and electrochemically corroded in a 3.5% NaCl solution. SEM, EDS, and electrochemical analysis are carried out to examine how cutting parameters affect the cutting force, surface quality, and corrosion resistance of cryogenically treated 7075‐T6 aluminum alloy. The results show that after cryogenic treatment, under different cutting speeds, the cutting force is up to 39.8% smaller than without cryogenic treatment; under different cutting depths and feed rates, the cutting force is up to 136% and 21.54% smaller, respectively. Cryogenic treatment dramatically reduces the cutting force in the cutting process. As cutting speed increases, machined surface quality becomes better; fewer corrosion products and cracks are induced. When the cutting depth is 1.5 mm, there are fewer plows and micro‐cracks on the machined surface than under other parameters, but cutting depth does not affect corrosion morphology significantly. The size of corrosion products is up to 55 μm smaller. The electrochemical analysis finds that at the cutting speed of 1500 m/min, after cryogenic treatment, the current density is 59.4% smaller than without cryogenic treatment; polarization resistance is 1.68 × 105Ω•cm2 larger. At the cutting depth of 1.5 mm, after cryogenic treatment, the current density is 66.16% smaller; self‐corrosion potential shifts 0.19 V toward the positive pole. At the feed rate of 0.06 mm/z, after cryogenic treatment, self‐corrosion potential shifts 0.18 V toward the positive pole; polarization resistance is 10.7% larger. These parameters correspond to the best corrosion resistance. [ABSTRACT FROM AUTHOR]

The present research aims to investigate the effects of friction stir welding (FSW) on the microstructure and mechanical properties of 7075-T6 aluminum alloy thin sheets. The welding has been performed perpendicular to the rolling direction of the sheets at three rotational speeds of 600, 1000, and 1600 rpm. From mechanical and microstructural points of view, a suitable welding condition has been recognized at 1000 rpm and welding speed of 50 mm/min. It is observed that with increasing the welding rotational speed more precipitates of the base metal are being dissolved in the metallic matrix and their distribution is more uniform. This phenomenon is recognized as the main mechanism of mechanical properties decline at 1600 rpm. Surprisingly 15,000 h after the welding process, the natural aging could not recover the precipitations within the welding zone of the specimen welded by 1600 rpm rotational speed. The effects of FSW on the three-dimensional forming behavior of the joints have been examined by the hemispherical punch stretching (HPS) method. Forming limit diagrams (FLD) of the weldments and the starting material have been measured and compared to each other. The formability examinations have demonstrated a 40% decline in the forming limit of the welded specimens in comparison to the base metal. The main reasons for the smaller formability of the welded specimens are comprehensively discussed.

The study predicts friction stir process (FSP) parameters using an artificial neural network (ANN) model. A design of experiment (DoE) approach is used to conduct experiments on FSP and to evaluate the best operating parameters of FSP. ANN uses 30 neurons, 1 hidden layer, and an input and output layer in the Matlab® environment. ANN predicts the output parameters with R values of 0.999, 0.995, and 0.992 for training, validation, and test datasets, respectively, while the overall R-value is 0.997. GRA is used to optimize and rank the parameters of the processes and revealed that the rotational tool speed should be 1180 rpm, traverse feed rate 38 mm/min, and tool tilt angle 1° for best results. The optimized values obtained are 380 MPa, 3.8 μm, 138 HV, and 14% for tensile strength, grain size, microhardness, and elongation, respectively. According to the analysis of variance (ANOVA) and grey relational analysis, the order of influencing parameters on output factors was rotational speed (80%), followed by transverse feed (19%) and tool tilt angle (1%). An ANN is further used to predict using the two most significant parameters--rotational speed and traverse feed. The modified ANN has nearly the same R values as the original ANN. Thus modified ANN may be used for prediction. [ABSTRACT FROM AUTHOR]

This study evaluates the influence of milling parameters on the milling process and microstructural changes in 7075-T6 aluminum alloy using experimental and simulation methods. Key findings include a direct correlation between milling parameters and higher chip temperatures, particularly influenced by milling speed which at its third level can cause temperature elevations up to 36 °C, ordered by impact as ap > f > v.Increasing milling depth markedly affects grain recrystallization, especially near the tool's trailing face (P3), leading to a 45.8% reduction in dynamic recrystallization, whereas lower depths expedite this process. Additionally, grain size and number at the leading face (P1) are also depth-dependent, with larger grains diminishing in volume yet increasing in quantity as depth increases. Enhanced milling speeds up to 500 mm/min significantly refine grains to near 1 μm at P1, with an 80.7% rise in recrystallization numbers, while at P3, grain size initially contracts then enlarges at 416 mm/min. Feed rate primarily impacts the quantity of recrystallized grains at the tool tip (P2), with a notable 60.4% increment and a swift transition from larger to smaller grains. Both P1 and P2 experience about a 20% reduction in grain growth due to feed rate, with more pronounced effects at P1 and the fragmentation of larger boundary grains into smaller, irregular shapes. • 7075 aluminum alloy machining microstructure evolution law was explored. • The influence of cutting parameters on microstructure evolution was explored. • The microstructure evolution of different deformation zones was compared. [ABSTRACT FROM AUTHOR]

The investigation on the formability of 7075-T6 aluminum alloy at elevated temperatures is significant due to its low plasticity at room temperature. Meso-Damage mechanics suggests that the growth and accumulation of micro-voids is an important factor that leads to material damage, fracture, and affects its formability. In this work, the Gurson–Tvergaard–Needleman (GTN) model was used to investigate the damage evolution of the 7075-T6 aluminum alloy during the hot forming process. The effects of different temperatures and strain rates on the formability were investigated through uniaxial hot tensile tests. The parameters of the Gurson–Tvergaard–Needleman (GTN) model were inverse-calibrated using the Central Composite Design (CCD)-Response Surface Method (RSM)-Genetic Algorithm (GA). Control variable method was used to explore the effect of each damage parameter on the fracture initiation and evolution. The results showed that the calibrated Gurson–Tvergaard–Needleman (GTN) model well predicted the high-temperature damage of the 7075-T6 aluminum alloy at 300–450 °C. Predicted necking and fracture volume fractions of voids were less than 3% error from experimental results. Initial void volume fraction (f0) had little effect on damage. Increasing void nucleation volume fraction (fN) significantly advanced the necking and fracture of the material. An increase in the critical void volume fraction (fC) and fracture void volume fraction (fF) resulted in higher peak stresses and fracture strains.

The small blind internal thread (SBIT) plays a very important role to firmly fastening some functional components on the cover of 3C electronic products. The small internal thread was made in a blind hole using a fluteless forming tap (FFT) without producing chips. However, the four geometric parameters of the FFT (tool width (W), tooth root diameter (D2), front-end diameter (Df), and tooth angle (θ)) will affect the thread filling rate (f) and minimum torque (T) in tapping process. This study reports the Box-Behnken design (BBD), combined with DEFORM-3D (finite element model) and MINITAB (regression analysis) software, to tap 7075-T6 aluminum alloy with small FFT to obtain reliable results of thread filling rate and minimum torque. The experimental results show that the BBD can accurately predict and simulate the thread filling rate of tapping 7075-T6 aluminum alloy. The modeling software and experimental design used in this research are very suitable for the optimal design of the FFT used in industrial production. [ABSTRACT FROM AUTHOR]

The effect of target condition (static and dynamic) and number of projectile impacts (single and multiple) on the ballistic performance of 6061-T6 Aluminum alloy, 7075-T6 Aluminum alloy and 6061- aluminum alloy Fiber Metal Laminates (FML) have been investigated. Both numerical and experimental approaches were used to predict the nature of target deformation and its kinetic energy absorption. Ballistic experiments were conducted using armor piercing projectiles (APP) of diameter 7.62 mm with velocities ranging between 330 to 450 m/s. Irrespective of the target material (6061-T6 aluminum alloy, 7075-T6 aluminum alloy), non-linear reduction of exit velocity of the projectile was observed for a single plate target. In contrast, large plastic deformation and 'petaling' mode of failure was observed for the FML and rubber sandwiched targets. Higher impact energy absorption of the FML target and rubber intruded 7075-T6 aluminum alloy plates is mainly due to the additional resistance offered by the individual layer of metal and fiber. In addition to projectile velocity, when the target (7075-T6 aluminum alloy plate) velocity was varied in the range of 10 to 40 m/s, significant reduction in exit velocity of the projectile was observed compared to static target. This is due the fact that, moving target has altered the penetration behavior of the projectile and additional increase of target velocity caused 'ricochet' of the projectile. In addition, when the target was subjected to multiple projectile impacts, gradual reduction of ballistic performance was observed. [ABSTRACT FROM AUTHOR]

Multi-energy field composite reinforcement technology has become a critical technique for improving the service life of key components in aviation engines. This paper aims to investigate the strengthening mechanism of high-speed cutting and solid particle-entrained waterjet peening (HSC-WJP) composite reinforcement on 7075-T6 aluminum alloy. Samples subjected to single solid particle-entrained waterjet peening (WJP) reinforcement were selected as the control group. The surface quality and microstructure evolution of 7075-T6 aluminum alloy after composite reinforcement were examined using SEM, EDS, XRD, TEM, and HRTEM techniques. The research results indicate that, under the same jet parameters, HSC-WJP composite reinforcement is superior to single WJP reinforcement in terms of surface roughness, except when the jet pressure is below 25 MPa and the track spacing is 0.53. The surfaces of the 7075-T6 aluminum alloy workpieces after reinforcement are mainly characterized by the presence of pits and micro-pores. Surface roughness shows a positive correlation with jet pressure and nozzle traverse speed. After HSC-WJP composite reinforcement, the surface roughness decreases by 0.132 μm compared to single WJP reinforcement, and the size of surface pits is reduced by 4–20 μm. Surface roughness decreases first, then increases, and then decreases again with increasing target distance, while it increases first and then decreases with increasing path spacing. A significant precipitation-free zone (PFZ) is present in the 7075-T6 aluminum alloy after reinforcement, and its width is positively correlated with the nozzle traverse speed. When the nozzle traverse speed is 120 mm/min, the average size of the PFZ at grain boundaries after single WJP reinforcement is 12–20 nm, while it decreases by approximately 3 nm after HSC-WJP composite reinforcement. The main precipitate phase in the reinforced aluminum matrix is η ′ phase, and under the same jet parameters, the HSC-WJP grain size is smaller, approximately 25–34 nm, and exhibits significant dislocation walls and dislocation tangles, with a higher dislocation density compared to single WJP reinforcement. • The influence mechanism of composite strengthening process on microstructure evolution was studied. • The effect of the composite hardening process on the surface characteristics was studied. • The process parameters of composite strengthening were optimized. [ABSTRACT FROM AUTHOR]

The welding with weld reinforcement rolling (WR) process was proposed to improve the deteriorated mechanical properties of traditional arc welded (TW) joints of the 7075-T6 aluminum alloy. In this novel process, the welding process and joint strengthening process were performed simultaneously. A comprehensive investigation of the microstructure evolution during the WR process was conducted. Ultimate tensile strength and elongation determined from tensile testing of the joints were 427.4 MPa, 5.5 % for WR joint and 301.3 MPa, 3.4 % for TW joint. The microhardness of the fusion zone (FZ) and heat-affected zone 1 (HAZ1, the dissolution zone) in the WR joint exceeded that of the TW joint. These results suggest that the application of rolling force not only affected the FZ but also simultaneously strengthened the HAZ1 through deformation while having a comparatively less effect on the heat-affected zone 2 (HAZ2, the over-ageing zone). Quantitative assessments of the effects of different strengthening mechanisms on the strength were conducted, and dislocation strengthening was found to be the predominant factor in increasing the strength of the WR joint. Deformation within both the FZ and HAZ1 during the WR process was mainly due to dislocation slip, while sub-grain rotation was also observed. • Welding with rolling process of 7075-T6 Al alloy was proposed. • Welding process and joint strengthening process were completed simultaneously. • The tensile strength of WR joint reached 81.4 % of the base metal. • The contributions of different strengthening mechanisms were calculated. • Dislocation slip dominates deformation, with sub-grain rotation supplementing. [ABSTRACT FROM AUTHOR]

7075 aluminum alloy is widely used in the aerospace field, and its use process is subjected to serious corrosion environment. This study aims to explore the influence mechanism of high-speed machining and shot peening water jet composite surface reinforcement on the corrosion behavior of 7075-T6 aluminum alloy. The 7075-T6 aluminum alloy was subjected to shot peening water jet (WJP) and high-speed machining combined with shot peening water jet (HSC-WJP) composite surface reinforcement treatments. The results showed that at a jet pressure of 20 MPa, a jet target distance of 7.5 mm, a nozzle moving speed of 660 mm/min, and a track spacing of 0.33 mm, the self-corrosion potential and polarization resistance were the highest, and the self-corrosion current density was the lowest, with the largest capacitance arc radius. Compared to the WJP treatment, the HSC-WJP-20MPa shifted the self-corrosion potential towards the positive direction by 0.01 V, increased the polarization resistance by 724 Ω cm2, and reduced the self-corrosion current by 7.9 %. The HSC-WJP-7.5 mm reduced the self-corrosion current density by 50.02 % and increased the polarization resistance by 24.9 %. The HSC-WJP-660 mm/min decreased the self-corrosion current density by 52.1 % and increased the polarization resistance by 44.5 %.The samples subjected to HSC-WJP composite reinforcement had fewer and smaller corrosion product sizes. • This study aims to explore the influence mechanism of high-speed machining and shot peening water jet composite surface reinforcement. • The 7075-T6 aluminum alloy was subjected to shot peening water jet (WJP) and high-speed machining combined with shot peening water jet. • The effects of composite reinforcement on the corrosion resistance of 7075-T6 aluminum alloy were investigated. [ABSTRACT FROM AUTHOR]

Surface mechanical attrition treatment (SMAT) is a method that enhances the mechanical properties of metallic materials by generating a thin nanostructured layer on the top surface. In this study, single-shot impact behavior was modeled for the 7075-T6 aluminum alloy to reach maximum values of equivalent stress, plastic strain, deformation depth, residual stress depth, and residual stress. Finite element simulations have been carried out to analyze the effect of selected parameters on stress and strains in the component. For simulating the SMAT process, a rigid sphere on a rectangular component is modeled using ANSYS/AUTODYN explicit dynamic solver. The plastic deformation process during SMAT was analyzed according to shot velocity and diameter with a dynamic explicit finite element method (FEM). The response surface methodology was used to evaluate the parametric results for the SMAT process. In addition, deformation behavior was evaluated after a single-shot impact according to the restitution coefficient. [ABSTRACT FROM AUTHOR]

High-strength 7075 aluminum alloy is widely used in the aerospace industry. The forming performance of 7075 aluminum alloy is poor at room temperature. Therefore, hot forming is mainly adopted. Electromagnetic forming is a high-speed forming technology that can significantly improve the forming limit of difficult-to-deform materials. However, there are few studies on electromagnetic hot forming of 7075-T6 aluminum alloy. In this study, the deformation behavior of 7075-T6 aluminum alloy in the temperature range of 25 °C to 400 °C was investigated. As the temperature increased, the sheet forming height first decreased, then increased. When the forming temperature is between 200 °C and 300 °C, η phase coarsening leads to a decrease in stress and hardness of the material. When the forming temperature is between 300 °C and 400 °C, continuous dynamic recrystallization of 7075 aluminum alloy occurs, resulting in grain refinement and an increase in stress and hardness. The results of numerical simulations and experiments all show that the forming height and deformation uniformity of the sheet metal are optimal at 400 °C, compared to 200 °C.

The effect of gradient nanostructure prepared by ultrasonic surface rolling on stress corrosion behavior of 7075-T6 aluminum alloy was studied. Results showed that gradient structure improved stress corrosion cracking (SCC) resistance-strength-ductility synergy. Grain refinement and dislocation proliferation offset strength reduction caused by the dissolution of precipitated phase. The superior SCC resistance was attributed to the reduction of surface roughness and the introduction of compressive residual stress. In addition, grain refinement, re-precipitation of coarse η phase at trigonal grain boundaries and the transformation of intracrystalline precipitated phase from GP zone to η' phase further enhanced SCC resistance. • Gradient nanostructured 7075-T6 aluminum alloy was successfully fabricated by ultrasonic surface rolling. • Gradient nanostructure simultaneously improved the SCC resistance-strength-ductility synergy of 7075-T6 aluminum alloy. • The improvement of SCC resistance of the alloy was related to surface roughness, residual stress and gradient structure. [ABSTRACT FROM AUTHOR]

The impact deformation behavior and associated microstructural evolution of 7075-T6 aluminum alloy at cryogenic temperatures are investigated using a compressive split-Hopkinson pressure bar (SHPB) system. Cylindrical specimens are deformed at strain rates of 1 × 10 3 s −1 , 2 × 10 3 s −1 , 3 × 10 3 s −1 and 5 × 10 3 s −1 and temperatures of 0 °C, −100 °C and −196 °C. It is shown that the flow stress is strongly dependent on the strain rate and temperature. For a given temperature, the flow stress varies with the strain rate in accordance with a power law relation with an average exponent of 0.157 and an activation energy of 0.7 kJ/mol. Moreover, the coupled effects of the strain rate and temperature on the flow stress are adequately described by the Zener-Hollomon parameter (Z). For all test temperatures, catastrophic failure occurs only under the highest strain rate of 5 × 10 3 s −1 , and is the result of adiabatic shear. An increasing strain rate or reducing temperature leads to a greater dislocation density and a smaller grain size. Finally, the dependence of the flow stress on the microstructural properties of the impacted 7075-T6 specimens is well described by a specific Hall-Petch constitutive model with constants of K = 108.3 MPa μm 1/2 and K ′ = 16.1 MPa μm, respectively. Overall, the results presented in this study provide a useful insight into the combined effects of strain rate and temperature on the flow resistance and deformability of 7075-T6 alloy and confirm that 7075-T6 is well suited to the fabrication of fuel tanks and related structural components in the aerospace field. [ABSTRACT FROM AUTHOR]

• Using 7075-T6 aluminum alloy and carbon fiber reinforced polyetheretherketone as research materials, the welding effect of blue laser and fiber laser oscillation welding was compared and discussed. • Due to the easy absorption characteristics of the blue laser wavelength, the obtained welded joint has fewer defects and twice the joint strength compared with fiber laser oscillation welding. • The resin embedded in the molten pool causes columnar crystals to grow around the resin, especially in fiber laser oscillation welding. • The established finite element model is in good agreement with the test results, and can effectively guide and predict the test results. Laser welding was employed to join aluminum alloys and carbon fiber reinforced polymers (CFRP) inexpensively and quickly in lightweight automobiles, especially in the field of new energy vehicles. In recent years, a new way to obtain stronger high-reflection alloy laser welded joints is blue laser welding (BLW). An innovative comparative experiment was conducted between blue laser welding (BLW) and fiber laser oscillation welding (FLOW), using 7075-T6 aluminum alloy and carbon fiber reinforced polyetheretherketone (CFRP-PEEK) as study materials, and the laser welding mechanism is explained. It was concluded that the maximum tensile force of the BLW joint was 478 N, which is higher than the 290 N tensile force of FLOW. In addition, the maximum residual stress in the BLW joint is 325 MPa, which is lower than that of FLOW. The mechanism affecting the strength of the joint is the presence of a larger number and size of bubble defects inside the FLOW melt pool, and the presence of a demarcation line between the columnar and equiaxed crystals around these bubble defects is observed. This boundary line means that there is a large temperature difference. Combined with the finite element simulation results, the existence of the temperature difference leads to a different solidification sequence around the bubble defect inside the molten pool, so stress concentration occurs. Therefore, the interface of the FLOW joint is not tightly combined, and a gap phenomenon occurs. Furthermore, when the laser power increases, PEEK resin is extruded into the melt pool as the melt pool size approaches that of the aluminum alloy, as observed in the BLW joint. The same demarcation line between columnar and equiaxed crystals structure was observed in the PEEK resin, so that the stress concentration around the PEEK resin can lead to weakened joints in high power welding. [ABSTRACT FROM AUTHOR]

The dynamic mechanical behaviors of 7075-T6 aluminum alloy at various strain rates were measured by dynamic tensile tests using the electronic universal testing machine, high velocity testing system and split Hopkinson tensile bar (SHTB). Stress–strain curves at different rates were obtained. The results show that the strain rate hardening effect of 7075-T6 aluminum alloy is significant. By modifying the strain rate hardening term in the Johnson–Cook constitutive model, a new Johnson–Cook (JC) constitutive model of 7075-T6 aluminum alloy was obtained. The improved Johnson–Cook model matched the experiment results very well. With the Johnson–Cook constitutive model, numerical simulations of tensile tests at different rates for 7075-T6 aluminum alloy were conducted. According to tensile loading and stress–strain relation of 7075-T6 aluminum alloy, calculation results were compared with experimental results. Accuracy of the modified Johnson–Cook constitutive equation was further proved. [ABSTRACT FROM AUTHOR]

A study on mechanical and fracture properties, through the experimentation techniques has been carried out on a Al 7075-T6 and it coated with an Electroless Nickel deposits of 10–20 μm in coating thickness. In the recent years there has been considerable interest in the Electroless Nickel plating due to its extensive use in electronics, automobiles, aerospace and other industries. Electroless Nickel plating is a controlled autocatalytic reduction of nickel ions using suitable reducing agent such as sodium hypophosphite. ASTM Standard – E 399 for plane strain fracture toughness determination was adhered in this investigation. The results obtained, show that the EN coating can give rise to a significant improvement in the fracture behavior (performance) of the substrate and also it has shown that EN coating exhibit a very good adhesive property to the alloy material when the tensile stresses exceeding the yield strength are applied to the system and performance of these pretreatments was studied by SEM analysis. [ABSTRACT FROM AUTHOR]

This work investigates the influences of water jet parameters, including jet pressure, nozzle moving speed, target range, and track interval, on the shot peening of 7075-T6 aluminum alloy. SiC pellets 0.1 mm in diameter are added into the water jet peening (WJP) process. The shot peened workpiece surface is then measured with a roughness tester, a microhardness METER, a METALLURGRAPHIC microscope (MO), and a scanning electron microscope (SEM). The influences of solid pellet WJP on workpiece surface roughness, microhardness, surface residual stress, and surface topography are examined. The results show that jet pressure is positively proportional to surface roughness and microhardness. However as nozzle moving speed and target range increase, the surface roughness and microhardness of the shot peened workpiece begin to decrease. At the track interval of 0.15 mm, the surface roughness of the treated workpiece is a minimum of 0.61 μm. The surface residual stress of the treated workpiece is also notably improved. The residual stress perpendicular to the trajectory is marginally higher than that along the trajectory, but the difference is limited. Further studies reveal that solid pellet WJF treatment of 7075-T6 is the most effective in the jet pressure interval of 25 MPã30 MPa. The optimal nozzle moving speed is 650 mm/miñ750 mm/min. The target range can be selected between 10 and 12.5 mm. The track interval must be greater than 0.1 mm. • This work investigates the influences of water jet parameters, including jet pressure, nozzle moving speed, target range, and track interval, on the shot peening of 7075-T6 aluminum alloy. • The influences of solid pellet WJP on workpiece surface roughness, microhardness, surface residual stress, and surface topography are examined. • Water jet parameter optimization is performed. [ABSTRACT FROM AUTHOR]

Abstract: The effect of hydrogen on the hardness of 7075-T6 aluminum alloy was investigated after experiments conducted on specimens that hydrogen charged under different cathodic charging conditions. Hardness measurements revealed that the introduction of hydrogen caused hardening on the surface of 7075-T6 aluminum alloy. The severity of the hardening increased with either cathodic current density or charging time. Further charging increased the depth of the hardened region of 7075-T6 aluminum alloy. Transmission electron microscopic observations of the hardened hydrogen-enriched layer revealed an increase in dislocation density. Aging after charging can result in either complete or partial recovery of hardness depending on the charging conditions applied to the material. [Copyright &y& Elsevier]

Abstract: The present investigation has been conducted in order to study the effect of the deposition of a ZrN coating, of ∼3μm in thickness, on the static mechanical properties and fatigue behavior of a 7075-T6 aluminum alloy substrate. It has been determined that the coating deposition process gives rise to a significant decrease in such properties, which is not fully compensated for the presence of the film. When fatigue tests were carried out in a 3wt.% NaCl solution at low alternating stresses, the ZrN film partially compensated for the decrease in fatigue properties of the coated substrate. Extensive delamination of the coating from the substrate was observed under the action of cyclic stresses greater than approximately 220MPa. Below this stress and in the presence of NaCl, the behavior of the coated material approached that of the uncoated alloy, which highlighted the good corrosion resistance of the ZrN coating and its ability to protect the substrate when it remained adhered to the latter. [Copyright &y& Elsevier]

Abstract: An investigation has been carried out in order to study the fatigue and corrosion–fatigue behavior of a 7075-T6 aluminum alloy coated with an electroless Ni–P (EN) deposit, in the as-plated condition, of approximately 38–40μm in thickness and a high P content, of approximately 18wt%. The results obtained, show that the EN coating can give rise to a significant improvement in the fatigue and corrosion–fatigue performance of the substrate, depending on the testing conditions. When the coated system is tested in air, it is observed that the increase in fatigue properties decreases as the alternating stress applied to the material increases. At stresses of the order of 0.4 σ 0.2% the increase in fatigue life is more than about 100%. However, as the stress increases to values in the range of 0.7 σ 0.2%, no improvement in the fatigue performance of the system is observed and the behavior is similar to that of the uncoated substrate. Under corrosion–fatigue conditions, the fatigue life is observed to increase between approximately 60% and 70%, depending on the stress applied. It is shown that fatigue cracks are associated with nodular-like defects present on the surface of the coated samples. The deleterious effect of such defects seems to be more pronounced as the alternating stress applied to the material increases. A crude estimate of the yield strength of the EN coating from tensile measurements indicates that such a parameter is in the range of 3.8 GPa, in agreement with the computation of the absolute hardness of the deposit, of about 4 GPa, by means of Meyer’s law. It is also shown that the EN deposit has a very good adhesion to the substrate even when the system is subjected to tensile stresses greater than the yield strength. Such characteristics as well as the higher mechanical properties of the EN coating in comparison with the aluminum alloy substrate and the preservation of its integrity during fatigue testing contribute to the better fatigue performance of the coated system. [Copyright &y& Elsevier]