Reaging Heat Research Articles

Fatigue behavior of notched and unnotched 7075-T6 aluminum alloy subjected to retrogression and re-aging (RRA) heat treatment and plasma nitriding

Aluminum alloys are widely used in aircraft components, which present the fatigue process as one of the main failure modes. The aeronautical industry has been searching for alternatives to increase the service life and safety of structural components. To address this issue, this work subjected the 7075-T6 alloy to retrogression and re-aging (RRA) heat treatment and plasma nitriding in order to obtain an improvement in the corrosion resistance. The objective was then to evaluate whether such treatments affected the fatigue behavior. Fatigue tests were carried out on the material with a smooth surface and with a notch (theoretical stress concentration factor of 5.7). A maximum likelihood estimation method was used to estimate the S-N curve parameters. The fatigue behavior without notch for the T6 and RRA treatments was similar, which is expected because the resulting microstructure of the RRA condition is composed of a homogeneous distribution of very fine η’ precipitates in the aluminum matrix, similar to the T6 condition. The worst fatigue behavior without notch was found for the material underplasma nitriding for two main reasons: the softening of the microstructure after processing and the substantial increase of the surface roughness. Regarding the notched material, the fatigue performance was reduced to a similar level regardless of the condition.

A trade-off between mechanical strength and electrical conductivity of Al–Zn–Mg–Cu alloy via Ag alloying and retrogression re-aging heat treatment

The effects of silver (Ag) alloying and a retrogression re-aging heat treatment on the mechanical properties and electrical conductivity of the Al–Zn–Mg–Cu aluminum alloy were studied by means of tensile test, electrical conductivity test, and transmission electron microscopy (TEM). A trade-off between the mechanical strength and electrical conductivity was achieved, with the former reaching 558 MPa and the latter reaching 45.1 IACS. The alloy was prepared through a retrogression re-aging heat treatment (120 °C/6 h + 160 °C/7 h + 220 °C/0.5 h + 120 °C/24 h) performed on the solution and quenched samples. Furthermore, through TEM analysis of the sample solution treated at Temperature Ⅰ (420 °C/3 h + 470 °C/2 h) and Temperature II (420 °C/3 h + 480 °C/2 h), indicates that the Ag interacts with zinc or magnesium to form small clusters, which can act as precursors for η′ precipitates. η–type precipitates were the dominant precipitated phase, and the precipitation sequence was supersaturated solid solution (SSS)→ small clusters → Guinier–Preston (GP) zone → η′ → η. Furthermore, after the retrogression re-aging heat treatment, a large amount of GP (Ⅱ) and η′ precipitated in the matrix. GP (Ⅱ) and the η′ phase are related to the precipitation of {111} Al crystal plane, it is thus speculated that the interaction between the η′ phase and GP (Ⅱ) or nanosized Al3Zr dispersoids contributes to the strength of the alloy. Moreover, the retrogression re-aging heat treatment promotes the precipitation of the second phase, which can purify the matrix and reduce lattice distortion, thus improving the conductivity of the alloy.

Microstructures and properties of wire-arc additively manufactured ultra-high strength aluminum alloy under different heat treatments

The microstructures, mechanical properties and corrosion behaviors of the ultra-high strength Al–Zn–Mg–Cu-Sc aluminum alloy fabricated by wire-arc additive manufacturing process using a self-prepared 7B55-Sc filler wire were systematically investigated under different heat treatments. The results showed that the microstructures of the as-deposited, T6, T73, and retrogression and re-aging (RRA) heat treatments were all composed of fine equiaxed grains with a size of about 6.0 μm. The grain boundary precipitates (GBPs) of the as-deposited sample were very coarse and continuously distributed along the grain boundaries, and the intragranular precipitates (IGPs) mainly consisted of a small amount of ηMg(Zn,Cu,Al)2 and η′ phases. After T6 heat treatment, the GBPs became much finer, but still continuously distributed along the grain boundaries. The IGPs mainly consisted of fine GP zones and η′ phases. After RRA heat treatment, the GBPs became coarser and discontinuously distributed along the grain boundaries. The IGPs were composed of η′ phases and ηMg(Zn,Cu,Al)2 phases. After T73 heat treatment, the GBPs became much coarser and sparsely distributed along the grain boundaries. The IGPs mainly consisted of coarser ηMg(Zn,Cu,Al)2 phases. The T6 heat-treated sample achieved the highest tensile strength of 618 MPa. While the strength of T73 heat-treated sample was sacrificed by up to 17% compared with the T6 heat-treated sample, but the corrosion resistance was the best of all heat-treated conditions. After RRA heat treatment, the strength was about 10% lower than the strength of the T6 condition, but the corrosion resistance was better than that of the T6 heat-treated sample.

Metallurgical characterization of natural aging effects on pre-deformed Al 7075/T651 alloy during retrogression and re-aging heat treatment

Metallurgical characterization of natural aging effects on pre-deformed Al 7075/T651 alloy during retrogression and re-aging heat treatment

Effect of regression and re-aging treatment on tensile yield strength anisotropy of 7050 aluminum alloy

In this study, the evolution rule of yeild strength and microstructure along the axial, hoop and radial directions of 7050 aluminum alloy ring forging during Regression and re-aging (RRA) heat treatment was studied by using the experimental technology of tensile property test and transmission electron microscope (TEM) and Electron backscatter diffraction (EBSD) observation. During the RRA process, the evolution rule of intragranular and intergranular precipitates along axial, hoop and radial directions of 7050 aluminum alloy ring forging was described by establishing a model. After the pre-aging stage, the yield strength of samples along the axial, hoop and radial directions of forgings shows obvious anisotropy, and the anisotropy decreases gradually after regression and re-aging treatment. The results show that the cause of the larger yield strength anisotropy is the inhomogeneous size and distribution of precipitates after the pre-aging stage; After the regression stage, the cause of the reduction of the yield strength anisotropy is due to the homogeneous distribution of intragranular precipitates; After re-aging treatment, the reasons of further reduction of the yield strength anisotropy are because of more homogeneous distribution of intragranular precipitates and the discontinuous of intergranular precipitates.

Effect of wear parameter on Al-Zn alloy on wear rate by using Taguchi’s technique

In this research article, an attempt is made to modify the Al-Zn alloy to know the influence of zinc content on microstructure and also the effect of wear parameter on wear rate for the modified alloy under different conditions. In the current research modification of Al-Zn alloy have been done by adding Zn in 5.1 wt%, 5.6 wt% and 6.1 wt% and Mg in 2.1 wt%, 2.5 wt% and 2.9 wt%. The modified Al-Zn alloy were subjected to Solutionzing treatment and followed by Retrogression Reageing (RRA) heat treatment. These Al-Zn alloys were cut and machined as per ASTM standard size. Irregular grain boundaries, grain size have been observed from the microstructure. Wear rate were found to be decrease with increase in content of zinc and reaging duration. Further, Taguchi’s Technique was adopted with three wear parameters with their three level each by using L27 (213) orthogonal array. ANOVA have been carried out to identify the percentage contribution of all the factor. It is evident that, the experimental results are good agreement with the predicted values during regression analysis.

Effect of Retrogression and Re-Aging Heat Treatment on Hardness, Tensile Strength and Microstructure of 7075 Aluminum Alloy

Retrogression and Re-Aging (RRA) Heat Treatment improves the tensile of aluminum alloys. In this research, to study the effect of Retrogression temperature and Retrogression time on the hardness, tensile strength and microstructure of 7075 aluminum alloy, have been applied. Retrogression treatments at different temperatures 180°C, 240°C and 370°C for 30 min and 90 min. When the retrogression temperature was 180°C for 30 min, the alloy has reached its highest hardness and tensile strength; they were respectively 165 HB and 586 MPa. RRA treatment of aluminum alloy 7075 led to precipitate a smoother, more homogeneous, and denser phase compared to the T6 treatment.

A research on the effect of retrogression and re-aging heat treatment on hot tensile properties of AA7075 aluminum alloys

Abstract Aluminium alloys are preferred in most industries due to the functional properties they provide. It is known that alloys that can be processed with heat treatments shows better mechanical properties. 7xxx series alloys can be processed vi heat treatments and are often used in environmental conditions such as extreme temperatures and corrosive environments. Corrosive sensitivities such as stress corrosion cracking (SCC) can be observed with the effect of working conditions. It is known that retrogression and re-aging (RRA) heat treatment provide corrosion resistance and decrease the SCC velocity. The purpose of this study is to examine the tensile behaviour of annealed and retrogression-re-aging (RRA) heat treated AA7075 alloys at elevated temperatures. The mechanical properties of the alloys were investigated by conducting tensile tests at room temperature (RT), 100, 200, and 300°C. Hardness tests were performed at room temperature on the samples which were taken from tensile test specimens after tensile tests. The potential effects of test temperature on mechanical and microstructural properties were examined. The annealed and RRA heat treated alloys were characterized by scanning electron microscope (SEM), and X-ray diffraction (XRD) analysis. As a result, an increase in strength and hardness of the RRA treated AA7075 alloys was observed. Ductility of the RRA alloy was lower compared to the annealed AA7075 alloy. Fracture surface examinations showed that there was a semi-ductile fracture below 200°C and ductile fracture at temperatures of 200 and 300°C. Ductility was observed to increase with increasing temperature.

INVESTIGATION OF THE EFFECTS OF DIFFERENT RETROGRESSION AND RE-AGING PARAMETERS APPLIED TO THE 7075 ALLOY ON THE MICRO-ARC OXIDATION PROCESS

In this paper, retrogression and re-aging (RRA) heat treatment was applied to 7075 aluminum alloy in T6 condition at different times (30 and 90[Formula: see text]min) and temperatures (180∘C and 240∘C). While RRA heat treatments increase the corrosion resistance of the material, it does not harm its mechanical properties. On the other hand, the surface resistance of aluminum is low. Surface modifications are applied to overcome this deficiency. Among these, the micro-arc oxidation (MAO) method increases the corrosion resistance and attains excellent values in surface hardness. To better understand the RRA/MAO relationship, heat-treated (RRA) samples with four different parameters were coated with the MAO method. In this way, a ceramic oxide coating layer was created on the material surfaces. In order to determine the RRA parameter effect, the MAO process parameters are kept constant (anode voltage ([Formula: see text]): 500[Formula: see text]V, cathode voltage ([Formula: see text]): 300[Formula: see text]V, anode voltage open time ([Formula: see text]: 300[Formula: see text][Formula: see text]s, cathode voltage open time ([Formula: see text]): 200[Formula: see text][Formula: see text]s, frequency: 160 coating with Hz, and process time: 20[Formula: see text]min). Surface properties (coating thickness, surface roughness, surface arc duct’s structure, etc.), phase analysis (X-ray diffraction (XRD)) and microstructures (coating cross-section studies: distance-dependent hardness, coating/backing material interface character, coating porosity ratio) were examined. XRD analysis showed that the main phase of the coatings is [Formula: see text]-Al2O3. A coating layer of around 125[Formula: see text][Formula: see text]m was achieved with the growth rate of 6[Formula: see text][Formula: see text]m/min. Surface roughness was between 5.5[Formula: see text][Formula: see text]m and 8[Formula: see text][Formula: see text]m for different RRA parameters. RRA/MAO relation with the characterization made was detailed, and predictions were made for the surface properties of the material (hardness, corrosion resistance, wear, etc.).

Retrogression and Reaging of AA7075 and AA6013 Aluminum Alloys

Retrogression and reaging (RRA) is of interest to the automotive industry for manufacturing components of high-strength aluminum alloys. RRA heat treatments are investigated for AA7075-T6 and AA6013-T6 materials. Retrogression is demonstrated to be a thermally activated process reasonably characterized with a single activation energy. Activation energies for retrogression are measured as 97 ± 7 and 160 ± 30 kJ/mol for AA7075-T6 and AA6013-T6, respectively. Critical retrogression times, tR* and t R max , are defined and measured across a range of retrogression temperatures. These data are used with the concept of reduced time to predict combinations of temperature and time that produce successful retrogression heat treatments. Recommended retrogression heat treatments are 200 °C for 3 to 12 minutes for AA7075-T6 and 240 °C for 7 minutes for AA6013-T6. Data from reaging heat treatments confirm a significant RRA response in AA6013. Recommended reaging heat treatments are 120 °C for 24 hours for retrogressed AA7075 and 190 °C for 1 hour for retrogressed AA6013. A reaging heat treatment that simulates the automotive paint-bake cycle, 185 °C for 25 minutes, is almost as effective as the recommended reaging heat treatment for AA6013 but is significantly less effective than the recommended reaging heat treatment for AA7075.

Uticaj termičkog tretmana retrogresije i ponovnog starenja na mehaničke karakteristike legure EN AW 7049A-T6

Aluminum alloys of 7xxx series have the highest strength among all aluminium alloys, but they are prone to the corrosion-induced damage. The retrogression and re-aging heat treatment (RRA) is a heat treatment process applied on the 7xxx series aluminum alloy in T6 temper condition to provide a significant improvement of the corrosion resistance with or without small loss in its strength. The paper presents the influence of RRA treatment on the electrical conductivity and mechanical properties of the aluminum EN AW 7049A-T6 alloy. The retrogression heat treatment was performed at various temperatures (from 180 C to 280 C) and times (from 3 min to 45 min), while re-aging was performed at 120 °C for 24 hours. It has been found that with increasing both temperature and time of retrogression, hardness and strength decrease but the toughness of the alloy increases in comparison to the initial T6 temper. Contrary to hardness values, electrical conductivity rises with an increase in holding time and temperature of retrogression.

Correlation between stress corrosion cracking resistance and grain-boundary precipitates of a new generation high Zn-containing 7056 aluminum alloy by non-isothermal aging and re-aging heat treatment

The new generation high Zn-containing 7xxx series aluminum alloys were more prone to stress corrosion cracking (SCC) compared with the traditional 7xxx series aluminum alloys. However, the effect of grain boundary precipitates (GBPs) characteristics, especially microchemistry, on SCC of new generation high Zn-containing 7xxx series aluminum alloys were not investigated in sufficient detail. In the paper, the GBPs characteristics of a new generation high Zn-containing 7056 aluminum alloy were prepared by different aging heat treatments. The morphology and microchemistry of GBPs were analyzed by transmission electron microscope equipped with super-X energy disperse spectroscopy. The stress intensity factor (KI) and SCC propagation velocity(v) were measured by double cantilever beam (DCB) experiment. The correlations between the GBPs microchemistry and SCC resistance had been discussed. The results showed that the SCC resistance of a new generation high Zn-containing 7056 aluminum alloy was significantly improved by high termination temperature non-isothermal aging and re-aging heat treatment compared with T6 and T77 aging heat treatment. In addition, it was indicated that the SCC resistance was positively with the Cu content of GBPs.

Effects of Different Heat Treatments on Mechanical Properties and Corrosion Resistance of Al-7.95Zn-1.84Mg-0.65Cu Aluminum Alloy

The effects of retrogression and re-aging(RRA) heat treatment on the mechanical properties and corrosion resistance of Al-7.95Zn-1.84Mg-0.65Cu aluminum alloy were investigated by hardness and tensile tests, as well as intergranular corrosion and transmission electron microscopy (TEM). The results show that the Al-7.95Zn-1.84Mg-0.65Cu alloy can obtain better hardness than the single-stage peak aging (T6) process after RRA process (120℃/24 h+200℃/10 min+120℃/24 h). At the same time, the tensile strength is 528.37 MPa, with 13.73% elongation and 29.4% increase in strong plastic product. The electrical conductivity is 40.47% IACS, the intergranular corrosion depth is only 59.43 μm, and the exfoliation corrosion grade is EA. The test results of transmission electron microscopy showed that the η' phase with larger size, greater strengthening effect and more obvious contrast is found in the alloy crystal after RRA treatment, and grain boundary precipitates (GBPs) become more discrete and coarser and precipitation-free precipitated zone (PFZ) becomes wider.

Enhancing the stress corrosion cracking resistance of a low-Cu containing Al-Zn-Mg-Cu aluminum alloy by step-quench and aging heat treatment

The influence of heat treatment on stress corrosion cracking resistance of a low-Cu containing Al-Zn-Mg-Cu aluminum alloy has been investigated. The results show that the stress corrosion cracking resistance is significantly improved by step-quench and aging heat treatment whereas retrogression and re-aging heat treatment and two-stage over aging heat treatment could hardly enhance the stress corrosion cracking resistance compared with peak aging. The improved stress corrosion cracking resistance of the low-Cu containing Al-Zn-Mg-Cu aluminum alloy subjected to step-quench and aging heat treatment is mainly attributed to grain boundary precipitates with high Cu content, large size and discontinuous distribution.

Investigation of the relationship between intergranular corrosion and retrogression and reaging in the AA6063

AbstractAA6063 was heat treated with different retrogression temperatures and durations, and the effect of heat treatment conditions on the microstructure, hardness, electrical conductivity, intergranular corrosion (IGC) and electrochemical corrosion behaviours of the AA6063 was determined compared with the T6 condition. The IGC test was applied according to the BS EN ISO 11846: 2008 standard. Moreover, potentiodynamic polarization tests were applied to determine the electrochemical corrosion behaviour of the heat‐treated samples. Electrochemical corrosion tests were carried out by using a Ivium Compactstat potentiostat in 3.5 wt.%. NaCl solution at 24°C with a scanning rate of 0.5 mV/s. The corrosion test cell consisted of the reference electrode (Ag/AgCl), working electrode (test sample) and a reference electrode (platinum). The effect of IGC on the microstructure of AA6063 and corrosion depth values was investigated by using a stereo optical microscope and a light metal microscope, respectively. Corrosion depth examinations were performed on microstructures taken from the cross‐sections of the samples. The chemistry of the precipitates formed at grain boundaries and distribution of the precipitates in the microstructure were investigated by scanning electron microscope, energy dispersive X‐ray and transmission electron microscope analyses. The results showed that retrogression and reaging heat treatment improves both the corrosion resistance and the mechanical properties of AA6063. After 50°C/15 min RRA heat treatment, the highest corrosion resistance and a higher hardness value than the T6 level were obtained.

Effects of retrogression and reaging heat treatment on the microstructure, exfoliation corrosion, electrical conductivity, and mechanical properties of AA7050

AbstractThe effects of different retrogression times and temperatures on the microstructure, electrical conductivity, exfoliation corrosion (EXCO), and hardness of the 7050 aluminium alloy were compared with the T6 and T7451 condition. The EXCO solution was prepared in accordance with ASTM G34‐01 standard and the samples were kept in the solution for 48 hr. Corrosion depths were examined by using scanning electron microscope (SEM) in the cross‐sections microstructure of the samples. The effect of EXCO on the material was investigated using stereo optical microscope images. In microstructure investigations, SEM and energy dispersive X‐ray (EDX) analyses were used to determine the distribution and chemistry of the precipitates at the grain boundaries. The results show that retrogression and reaging (RRA) times and temperatures have significant effects on AA7050 EXCO. Especially after 200°C/30 min RRA process, it has been found that 7050 aluminium alloy has higher mechanical strength than T6 level and high corrosion resistance from T7451 level. According to the results of this study, it has been shown that there is a direct connection between electrical conductivity and EXCO.

Optimization of Heat Treatment Cycles and Characterization of Aluminum Alloy AA7010

Multistage retrogression and reaging (RRA) heat treatment has been carried out on aluminum alloy AA7010. Each of the heat treatment steps for this alloy has been optimized on the basis of preliminary hardness and electrical conductivity measurements. These values were found to be a function of precipitate morphology and distribution. Samples were solution-treated (ST) with three different temperatures and quenching media, further aged at fixed temperature (120 °C) with time ranging from 24 to 120 h. Retrogression and reaging is done at 180-240 °C (for time duration of 2-60 min) and 120 °C (for 24-90 h), respectively. ST at 480 °C followed by warm water quenching (70 °C), aging cycle for T6 and T73 condition: 120 °C/42 h and 170 °C/128 h were found to be optimum. The optimum RRA conditions were achieved at retrogression parameters of 200 °C for 60 min and 240 °C for 60 min along with aging parameters of 120 °C/30 h and 120 °C/36 h, respectively. TEM images showed the presence of uniformly distributed precipitates in the matrix in RRA conditions. Statistical distribution of precipitates showed higher frequency of precipitates for RRA with optimized conditions RA1 (120 °C for 42 h + 200 °C for 60 min + 120 °C for 30 h) and RA2 (120 °C for 42 h + 240 °C for 60 min + 120 °C for 36 h).

Influence of retrogression and re-ageing heat treatment on the fatigue crack growth behavior of 7010 aluminum alloy

Aluminum alloys are widely used in aircraft structural components where light weight, high strength and good corrosion resistance are the primary requirements. These alloys are generally used in peak-aged (T6) condition in which they are susceptible for stress corrosion cracking. In the recent years, retrogression and re-ageing (RRA) treatment on aluminum alloy is carried out to enhance their corrosion resistance maintaining the ultimate tensile strength. The aim of this work was to study the influence of RRA treatment on the fatigue crack growth rate (FCGR) behavior. The 7010 aluminum alloy was heat treated to two different conditions i.e., T6 and RRA. The microstructures of these alloys were characterized by using TEM. Standard compact tension (CT) specimens were prepared and FCGR tests were carried out by using a 100 kN servo-hydraulic test machine as per ASTM E647-15e1. The constant amplitude FCGR tests were carried out at a stress ratio, R = 0.5 using sine wave loading pattern at 10 Hz. Crack length was monitored by following compliance technique. Microstructural studies show that RRA treated alloy contain fine and densely populated precipitates in the matrix along with coarse and discontinuous precipitates in the grain boundary. The fatigue crack growth rate was observed to reduce along with an increase in the threshold stress intensity factor range (ΔKth) for RRA treated alloy compared to the T6 alloy. The mechanisms for reduction in fatigue crack growth rate of RRA treated alloy is attributed to the microstructural modifications. The increased resistance is expected to enhance the damage tolerance capability of the alloy.

Study on Corrosion Behavior of 7075 Aluminum Alloy with Retrogression and Reaging Using Taguchi Method

The corrosion resistance and mechanical properties of 7075 aluminum alloy are improved by retrogression and reaging (RRA) heat treatment. Due to the complex process of RRA heat treatment, a Taguchi L25 orthogonal array is designed to optimize the process parameters of RRA heat treatment. In this work, analysis of variance was performed to find out the significant heat treatment parameters. Microstructure, mechanical properties, intergranular corrosion, exfoliation corrosion and stress corrosion cracking behaviors of 7075 aluminum alloy after RRA heat treatment were investigated by tensile test, slow strain rate test, transmission electron microscope and scanning electron microscope. Results showed that the RRA treatment involving preaging at 120 °C for 16 h, retrogression at 200 °C for 8 min and reaging at 120 °C for 24 h resulted in a desired combination of corrosion resistance and mechanical properties.

Influence of Potential Scan Rate on Corrosion Behaviour of Heat Treated AA 7075 Alloy in Sulphuric Acid Solution

In this paper, the effect of scan rate on the corrosion parameters and electrochemical behaviour of Retrogression and Re-aging (RRA) heat treatment of 7075 aluminium alloy has been investigated by Potentiodynamic polarization (PD) and electrochemical impedance spectroscopy (EIS) methods. The Potentiodynamic polarization (PD) curves were obtained at various scan rates for aged aluminium alloys in 0.5 M H2SO4 solution. The results show that at high scan rates shows unpredicted fluctuation of charging current, whereas at lower scan rates fewer disturbances are observed. The aged samples were chemically and mechanically characterized. It was observed that the RRA at 0.7 h shown improved corrosion property as well as mechanical properties compared to T6 temper. The corrosion properties were confirmed by EIS and polarization experiments.