Retrogression And Re-aging Treatment Research Articles

Effect of Retrogression with Different Cooling Ways on the Microstructure and Properties of T'/η' Strengthened Al-Zn-Mg-Cu Alloys.

Retrogression and re-aging (RRA) treatment has been proven to effectively overcome the trade-off between strength and corrosion resistance. Current research focuses on the heating rate, temperature, and holding time of retrogression treatment while ignoring the retrogression cooling ways. In this paper, the effects of RRA treatment with different retrogression cooling ways on the microstructure and properties of newly developed T'/η' strengthened Al-Zn-Mg-Cu alloys were investigated by performing tests on mechanical properties, intergranular corrosion (IGC) resistance, and electrochemical corrosion behavior. The results show that the mechanical properties of samples subject to RRA treatment with water-quenching retrogression (ultimate tensile strength, yield strength, and elongation of 419.2 MPa, 370.2 MPa, and 15.9, respectively) are better than those of air-cooled and furnace-cooled samples. The corrosion resistance of water-quenching (IGC depth of 162.2 μm, corrosion current density of 0.833 × 10-5 A/cm2) and furnace-cooled samples (IGC depth of 123.7 μm, corrosion current density of 0.712 × 10-5 A/cm2) is better than that of air-cooled samples. Microstructure characterization reveals that the effect of the retrogression cooling rate on mechanical properties is related to the size of T'/η' precipitates with grains as well as the proportion of T' and η', while the difference in corrosion resistance depends on the continuity of grain boundary precipitates (GBPs). With mechanical properties, corrosion resistance, and time cost taken into consideration, it is appropriate to select water quenching for retrogression. These findings offer valuable insights for further design to achieve superior performance in various applications.

Effects of Aging Treatments on the Age Hardening Behavior and Microstructures in an Al-Mg-Si-Cu Alloy

In this study, we investigated the effects of modified aging treatments on the microstructures and hardness in a commercial 6016 Al alloy through hardness tests and transmission electron microscopy (TEM) observations. The results demonstrate that many fine needle-like β″ phases contribute to the high hardness of peak-aged (T6) alloys. Over-aging treatments lead to the precipitation of lath-like β′, β″/disordered, or B′/disordered composite phases. Moderate over-aging treatment results in the coarsening of grain boundary precipitates (GBPs) and widening of the precipitate-free zone (PFZ), while heavy over-aging treatment triggers the re-precipitation of Cu-containing GBPs and increases the number density of GBPs. A retrogression and re-aging (RRA) treatment precipitates β″, lath-like β′, and disordered phases, while a two-step aging (T78) treatment precipitates β″, B′, and disordered phases. Both the T78 and the RRA treatments lead to the coarsening of GBPs and the widening of PFZs. The decreased hardness during over-aging treatments is attributed to a combination of coarsening intragranular precipitates and/or wider PFZs. The T78 and RRA tempers achieve 95.5% and 94% of the hardness values of the T6 treatment, respectively. The hardness values of the RRA and T78 treated alloys are related to the finer nano-sized precipitates formed during the high temperature process. These precipitates can compensate for the loss of hardness caused by the increase in the widths of the PFZs and the coarsening of the matrix precipitates. The relationship between the hardness and microstructures such as PFZs and precipitates in the matrix during various heat treatments is elucidated.

Enhancing properties of Al-Zn-Mg-Cu alloy through microalloying and heat treatment

This paper aims to understand the influence of microalloying constituents (Ti, Zr, Sr and Sc), and three heat treatment conditions i.e., T6, retrogression and reaging (RRA) and high temperature aging (HTA) on mechanical and thermal characteristics of modified Al-Zn-Mg-Cu-X alloy using microstructural analyses consist of precipitation characteristics, phase fraction and phase morphology. Addition of 0.25 wt % Sc significantly refines the grain structure, reducing the grain size from 62 μm to 34 μm and increasing Al3Zr, Al3(Zr, Ti), and Al3(Sc, Zr) precipitate fraction. After T6 aging, the alloy exhibits primary precipitates of fine η and T phases, accompanied by secondary intermetallics as well as S phases. RRA treatment led to a slightly larger fraction of coarse Zn and Cu-rich phases, while HTA results in larger η, T, and S phases due to high-temperature aging. The addition of Sc reduces the cooling rate by raising the transition temperature to 532 °C with an enthalpy of 22.1 J/g. T6 treatment shows dissolution of most η phases within the matrix, although RRA and HTA exhibit higher enthalpy due to a greater fraction of η phases. The tensile strength of Al-Zn-Mg-Cu-X alloy follows the following sequence: T6 > RRA > HTA > as-cast condition, regardless of micro-alloy additions. Under T6 conditions, Sc added alloy achieves 30 % higher strength, i.e., 575 MPa, than base alloy due to fine dispersoids. RRA treatment enhances elongation without compromising mechanical properties, resulting in a shift from transgranular brittle fracture to intergranular-dominated mix-mode fracture, with the presence of secondary cracking.

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.

Investigation on strength, toughness and microstructure of cryogenically-deformed 7A85 aluminum alloy under various aging tempers

The strength, fracture toughness, electrical conductivity, and microstructure evolution of cryogenically-deformed 7A85 aluminum alloy at different aging temperatures and aging times of single-step (T6), double (T74), and retrogression and re-aging (RRA) treatments were investigated. The results showed that the high-strength samples under T6 had low electrical conductivity and fracture toughness, which were significantly improved under T74 and RRA. Upon extending the aging time, the strength and intergranular fracture proportion increased and the fracture toughness decreased under T6, while the strength decreased and the transgranular fracture proportion and fracture toughness increased under T74 and RRA. The electrical conductivities were improved under T6, T74, and RRA by prolonging the aging time. The recommended single-step, double, and RRA aging tempers for cryogenically-deformed 7A85 aluminum alloy were T624 (120 °C/24 h), T742 (120 °C/6 h + 170 °C/2 h), and RRA0.5 (120 °C/24 h + 180 °C/0.5 h + 120 °C/24 h), respectively. By comprehensively considering the conductivity, fracture toughness, and mechanical properties, the optimal aging temper for the cryogenically-deformed 7A85 aluminum alloy was RRA0.5. Compared with T624, the fracture toughness of T742 and RRA0.5 increased by 38.7% with a certain strength loss and by 10.4% without strength loss, respectively. For the RRA treatment, the matrix precipitates were similar to the T6 state and the grain boundary precipitates were similar to the T74 state. The effect of heat treatment on the strength and fracture toughness could be explained by the cutting mechanism, the Orowan mechanism, and the strength difference between the matrix and grain boundaries.

Effect of three-dimensional deformation at different temperatures on microstructure, strength, fracture toughness and corrosion resistance of 7A85 aluminum alloy

In this study, 7A85 aluminum alloy was subjected to 20% three-dimensional (3D) deformation at different temperatures (−196, 25, 250, and 480 °C), followed by solid solution, water quenching, 3% cold deformation, and retrogression and re-aging (RRA) treatment. The microstructural evolution and 3D mechanical properties, fracture toughness, electrical conductivity, and corrosion resistance of the alloy under different deformation processes were analyzed for comparison. The results indicated that conducting the 3D deformation process prior to solution treatment significantly improved the strength and fracture toughness of the alloy as compared to the undeformed (UD) specimen, and maintained its good corrosion resistance under the RRA treatment. In addition, with the decrease of the deformation temperature, the greater flow stress strongly sheared and crushed the coarse second-phase particles into fine particles, thus facilitating their full dissolution in the aluminum matrix during subsequent solution treatment and increasing the driving force for aging precipitation. Furthermore, more dislocations were introduced at low-temperature deformation, thus providing more nucleation sites for static recrystallization during solution treatment and refining grains. Ultimately, the densest precipitates and the finest equiaxed grains with the narrowest grain boundary precipitate-free zones (PFZs) were acquired for the cryogenic deformation (CD) sample, resulting in the highest ultimate tensile strength (UTS), elongation (EL) with the least anisotropy, and fracture toughness of the CD specimen. The optimal comprehensive performance was obtained for the CD specimen with the average 3D UTS, average 3D yield strength (YS), average 3D EL, and fracture toughness of 545 MPa, 476 MPa, 16%, and 42.49 MPa·m1/2, respectively, which were respectively 2.3%, 0.2%, 18.5%, and 21.4% higher than those of the UD specimen.

Microstructure analysis of 7050 aluminum alloy processed by multistage aging treatments

In the current study differential scanning calorimetry (DSC) and transmission Electron Microscopy (TEM) analyzes were performed in order to investigate the bimodal microstructure feature by taking into account both density and morphology of precipitates, which are transformed from the retrogression and reaging (RRA) along with interrupted aging (T6I4) conditions within the 7050 aluminum alloy. Results showed that RRA treatment is conducive to a higher density of fine precipitates distributed homogeneously in the Al matrix, with precipitates essentially being shear-resistant η’ in view of a smaller density of shearable GP zone and incoherent η precipitates present. Conversely, the T6I4-65 treatment generated a smaller density of less fine shear-resistant precipitates, but with a higher density of shearable GP zone and incoherent η precipitates. Thus, the RRA treatment might promote a beneficial effect on correlation between yield strength and ductility owing to higher balance of combination mechanisms between shearable GP zones and shear-resistant η’ precipitates with movement dislocations as opposed to T6I4-65 treatment within the 7050 aluminum alloy. Both RRA and T6I4-65 treatments culminated in a slight decrease in either potential or pitting corrosion in comparison to the T7451 treatment.

Influence of aging treatment on the microstructure, mechanical properties and corrosion behavior of Al-Zn-Mg-Sc-Zr alloy

The precipitation behaviour, mechanical properties and corrosion performance of an Al-Zn-Mg-Sc-Zr alloy under one-stage aging (T6), two-stage aging (T74) and retrogression and re-aging (RRA) treatment were mainly investigated. For the RRA treatment, with increasing temperature and duration of retrogression, the grain interior precipitates (GIPs) gradually grew and changed from GP zones + η′ phases to η′ phases + η phases. In addition, the discontinuity of coarsened grain boundary precipitates (GBPs) significantly increased, and the width of precipitate free zones (PFZs) became broader. Consequently, progressive decrease in strength and hardness, and improved corrosion resistance of the alloy can be observed. Compared to conventional T6 and T74 treatments, a good balance of mechanical properties (168.5 HV for hardness, 547 MPa for ultimate tensile strength) and corrosion resistance can be obtained with retrogression treatment at 160 °C for 30 min. Moreover, research on the localized corrosion of the Al-Zn-Mg-Sc-Zr alloy showed that, at the initial stage of pitting corrosion, the Al matrix around the cathodic α-Al(Fe,Mn)Si particles was uniformly dissolved, leading to the detachment of the α-Al(Fe,Mn)Si particles from the matrix and the formation of pitting pits.

Effects of retrogression and re-aging treatment on precipitation behavior, mechanical and corrosion properties of a Zr+Er modified Al-Zn-Mg-Cu alloy

The microstructure, mechanical properties, and corrosion resistance of a Zr + Er modified Al-Zn-Mg-Cu alloy after different retrogression and re-aging (RRA) treatments were investigated. Results show that the main precipitates after different heat treatment change from GP zones + η’ + Al 3 (Er, Zr) phase (T6) to η’ + Al 3 (Er, Zr) phase (RRA180–30) and then to η + T phase (RRA200–30). The component, size, and distribution of precipitated phases would be affected by the regression time and temperature during RRA treatment. It is concluded that the uniformly dispersed precipitate phase in matrix and narrow precipitate-free zones (PFZs) could significantly improve the strength of Al-Zn-Mg-Cu alloy, and the grain boundary precipitated phase (GBPs) with moderate size and large interparticle distance could improve the alloy's corrosion resistance. Besides, a wider PFZ within a certain range is beneficial to improve the intergranular corrosion (IGC) performance. Therefore, it is important to accurately control the heating temperature and retrogression time during the retrogression stage to regulate the characteristics of precipitated phases and achieve the best balance of mechanical properties and corrosion resistance. • The precipitates size of RRA sample was larger and discontinuously distributed in GB. • Uniform precipitates in matrix and narrow PFZ are beneficial to the alloys' strength. • Corrosion resistance was improved with increasing retrogression temperature and time. • The wide PFZ and discontinuous GBP could improve the IGC resistance of the alloy.

The effect of various RRA treatments on the strength and corrosion behavior of a new type of Al–Zn–Mg–Er–Zr alloy

AbstractThe effect of various retrogression and reaging (RRA) treatments on the strength and corrosion behavior of a new type of Al–Zn–Mg–Er–Zr alloy has been investigated by hardness testing, tensile testing, and evaluating the intergranular corrosion (IGC) and exfoliation corrosion (EXCO) behavior. The results show that the RRA treatment can effectively improve the IGC and EXCO resistance by sacrificing less strength due to the formation of grain interior precipitates and the grain boundary precipitates similar to the T6 temper and T73 temper, respectively. At the peak value of the hardness, the alloy retrogressed at 190°C shows the better IGC and EXCO resistance; the alloy retrogressed at 170°C exhibits the higher strength. The optimal combination of strength, IGC and EXCO resistance is obtained after retrogression at 180°C for 60 min. For the different heat‐treatment tempers, the corresponding microstructure evolution of the precipitates, including Al3(Er,Zr) particles is discussed in detail.

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.

Influence of Retrogression and Reaging Treatment on Microstructure and Microhardness of the 3A21/7075 Aluminum Alloy Cladding Material

The 7075 aluminum alloy was an important structural material in the field of aeronautics and astronautics. With the development of this field, the requirements for its comprehensive properties were increasing. A novel casting method, the impact jet solid-liquid compound casting, was adopted to fabricate the 3A21/7075 aluminum alloy cladding material. Retrogression and reaging (RRA) treatment was further applied to the 3A21/7075 aluminum alloy cladding material in order to investigate the influence of RRA on microstructure and microhardness of the 3A21/7075 aluminum alloy cladding material. Then, the electron backscattered diffraction (EBSD) technique and the transmission electron microscope (TEM) together with the energy dispersive spectrometer (EDS) and the hardness test were utilized to analyze the influence of RRA treatment on microstructure and hardness of the 3A21/7075 aluminum alloy cladding material. The research results showed the 3A21/7075 aluminum alloy cladding material had better deformability. The amount of fine and dispersed phases precipitated in grains was in favor of improving the comprehensive mechanical properties of the 3A21/7075 aluminum alloy cladding material. This research might provide data and a theoretical approach for the engineering application of the 3A21/7075 aluminum alloy cladding material.

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.

Effects of Retrogression Treatment Process on the Mechanical Properties and Corrosion Behavior of the Graphene/7075 Aluminum Matrix Composite

The influence of various retrogression and re-ageing (RRA) treatment processes on the hardness, electrical conductivity and corrosion behavior of graphene/7075 aluminum matrix composite were investigated. The results showed that the hardness decreased swiftly at the initial stage and short time to peak value as the retrogression temperature (170 °C, 180 °C, 190 °C, 200 °C) rises. In the RRA 180 °C/120 min process, the electrical conductivity and peak-aging Brinell hardness were 37.9%IACS, 192.8. This RRA treatment possessed excellent pitting corrosion resistance, and the corresponding pitting potential (Epit), the passivation potential (Epit-Ecorr), the pitting corrosion current density (Logicorr) were -0.756V, 0.558V, -1.836A/cm2, respectively. This enhance can attribute that the continuous η phase distributed along the grain boundary became intermittent and coarse in the retrogression stage.

Electrochemical and Exfoliation Corrosion Behavior of Reversion-Treated High-Strength Aluminum Alloy

The present study aims to understand the microstructural modification affecting the electrochemical and exfoliation corrosion (EXCO) characteristics of aluminum alloy 7010. The alloy was aged for two different tempers, namely peak aging (T6) and retrogression and re-aging (RRA). The standard electrochemical polarization tests and EXCO tests were performed on the treated alloys. The microstructure of the alloy observed under a scanning transmission electron microscope revealed the presence of continuous grain boundary precipitates in T6 alloy. These precipitates were formed discontinuously after RRA treatment. The RRA alloy microstructure resulted in a shift toward positive potential. The exfoliation corrosion depth was reduced to 60–70 μm after RRA treatment, which was measured to be about 250 μm in T6 condition. The resistance toward the exfoliation corrosion was found to be influenced by the enriched Cu content of precipitates on grain boundary after reversion treatment. The results confirm that the RRA-tempered alloy improves both electrochemical corrosion and EXCO resistance.

Effect of retrogression treatments on microstructure, hardness and corrosion behaviors of aluminum alloy 7085

The microstructure, hardness and corrosion resistance of aluminum alloy 7085 after different retrogression and re-aging (RRA) treatments were investigated. The results showed that the properties of alloy 7085 are sensitive to the temperature and dwell time of the retrogression treatment. Desirable mechanical property and corrosion resistance can be obtained for the alloy pre-aged at 120 °C for 24 h, followed by a retrogression at 160 °C for 1.5 h and re-aging at 120 °C for 24 h. After the optimized RRA treatment, the hardness of alloy 7085 is improved by 10.2% as compared with the peak-aged one, which is mainly due to the distribution of dispersed rod-like η′ precipitates in the matrix; while the improved corrosion resistance is mainly attributed to the discrete and coarse η phase with higher Cu content, and narrow precipitate-free zone about 45–50 nm in width along the grain boundaries.

Effects of multi-stage aging treatments on the precipitation behavior and properties of 7136 aluminum alloy

The solutionized 7136 Al alloy was heat treated by one-step aging, two-step aging, retrogression and re-aging (RRA) and RRA plus further aging treatment, respectively. The influences of different aging treatments on the precipitation behavior, electrical conductivity and tensile properties were investigated. The results showed that one-step aging treatment forms continuous grain boundary precipitates (GBPs), coherent Guinier-Preston (GP) zone and semi-coherent η’ grain interior precipitates (GIPs). By two-step aging treatment, the GIPs are coarsened and partly transformed into incoherent η phase, which result in a reduction of strength but an enhancement of ductility and electrical conductivity. RRA treatment makes the GBPs to be discontinuous and forms precipitates free zone (PFZ) near grain boundary. The RRA alloy shows similar strength but higher electrical conductivity in comparison with one-step aging. When the RRA alloy further aged at 160 °C, the strength keeps almost constant until 10 h, while the electrical conductivity is increased with increasing aging time. The PFZ is widened and the GIPs become coarser by further aging at high temperature. By contrast, the PFZ is eliminated, accompanying with the formation of GP(II) as further aged at low temperature of 70 °C, therefore a higher strength and lower electrical conductivity are obtained.

Effect of Local Postweld Heat Treatments on Metal Inert Gas-Welded A7N01S-T5 Joints

T6, T7, and retrogression and reaging (RRA) postweld heat treatments (PWHTs) were redefined and deployed to restore MIG-welded A7N01-T5 aluminum alloy joints in train-body structures using an inductive heating device. After the PWHT, the microstructures and mechanical properties of the joints were studied by x-ray diffraction (XRD), electron backscattered diffraction (EBSD), and scanning electron microscopy (SEM). The results showed that the hardness and strength of the joints were improved by the T6 treatment, and the tensile strength of the joints reached 87.39% of the base metal. However, an improvement in the corrosion resistance was not observed. The T7-treated joints enhanced the toughness of the welded joints and improved their corrosion resistance. The RRA-treated joints improved the toughness and corrosion resistance and increased the strength and hardness. The RRA treatment had a more comprehensive effect on the improvement of the welded joint structure and performance and is more suitable for postweld heat treatment of the aluminum alloy welded joints in the body of high-speed trains.

Effect of Heat and Mechanical Treatments on Mechanical Properties of Al-Zn-Mg-Cu Alloys

In this research the effect of various heat treatments on tensile properties and hardness of Aluminum-Zinc-Magnesium-Copper alloy (7075 Aluminum alloy) was studied, with and without mechanical treatment by extrusion process. The 7075 alloy samples were submitted to two type of heat treatments, T6 heat treatment by artificial ageing samples in 120 ºC for 24 h and retrogression and re-ageing (RRA). Where in RRA treatment the first ageing done in 120 ºC for 24 h, then the retrogression done in 180 ºC for 30 min and re-ageing in 120 ºC for 24 h. We got the best results by apply the RRA treatment with extrusion process, where tensile strength was reached to 380 Mpa without extrusion machining process, while reached to 530 Mpa with extrusion process

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.