Two-stage Aging Treatment Research Articles

Microstructure Evolution and Mechanical Properties of TiB2/Al–Cu–Mn–Cd Composite with the Adoption of Two-Stage Solution and Aging Treatment

Microstructure Evolution and Mechanical Properties of TiB2/Al–Cu–Mn–Cd Composite with the Adoption of Two-Stage Solution and Aging Treatment

Two-stage aging treatment to accelerate aging kinetics without impairing strength in B4C/7A04Al composite

Two-stage aging treatment to accelerate aging kinetics without impairing strength in B4C/7A04Al composite

Microstructural and mechanical properties of additive manufactured 2319 aluminum alloy annular-shaped components: As-built and multistage heat treatment

A novel multistage aging heat-treatment method was applied to investigate the microstructural evolution and properties of an additive-manufactured 2319 aluminum alloy. The microstructure and mechanical properties were analyzed, and the results revealed that the as-built annular-shaped components were characterized by an alternating distribution of thin equiaxed crystals, dendrites, and coarse columnar crystals. The microstructure occurs recrystallization and the average grain size decreased after the two-stage aging treatment. The maximum texture strength in the selected area increased after the two-stage aging treatment, and the angle grain boundaries were evenly distributed. Solid solution plus aging could significantly improve ultimate tensile strength and hardness. The tensile fracture morphology was typical of ductile fracture. Two-stage aging exhibited a higher corrosion resistance.

The influence of electron beam welding technology on mechanical properties of GH4169 welded joints

Super-alloy GH4169 and related welded structures were widely used in the aero-engine industry region. Vacuum electron beam welding is one of the most advanced welding technologies, and the influence of the mechanical property caused by the welding technology still needs further research. Firstly, the hardness, microstructure, and tensile properties of the GH4169 electron beam welded joint were tested. After electron beam welding and two-stage aging treatment, the weld zone was strengthened and its hardness is higher than that of the base metal zone. The microstructure characterization results showed that the grain size of the weld and heat-affected zone was larger than that of the base metal. The tensile results show that the static properties of the welded joint are similar to that of the base metal, and the residual height has no obvious effect on the static strength of the welded joint. The high-temperature creep properties of GH4169 electron beam welded joints with residual height were tested. The results show that residual height will lead to a transient fracture of welded joints under relatively safe service conditions. The fatigue performance of GH4169 welded joints with and without residual height was tested respectively. The results show that the fatigue life of the welded joints without residual height was about 10 times longer than that of the welded joints with residual height under the same stress level, and for the welded joint with residual height, the residual height position will become the main fatigue crack source.

Effect of Final Thermomechanical Treatment on the Mechanical Properties and Microstructure of T Phase Hardened Al-5.8Mg-4.5Zn-0.5Cu Alloy.

The effect of final thermomechanical treatment (FTMT) on the mechanical properties and microstructure of a T-Mg32(Al Zn)49 phase precipitation hardened Al-5.8Mg-4.5Zn-0.5Cu alloy was studied. The as-cold rolled aluminum alloy samples were subjected sequentially to solid solution treatment, pre-deformation, and two-stage aging treatment. Vickers hardness was measured during the aging process under various parameters. Tensile tests were conducted on the representative samples based on the hardness results. Microstructural characteristics were analyzed via transmission electron microscopy and high-resolution transmission electron microscopy. The conventional T6 process was also carried out for comparison. The hardness and tensile strength are increased evidently by the FTMT process for the Al-Mg-Zn-Cu alloy, while the ductility is adversely affected to a small extent. The precipitation at the T6 state consists of a coherent Guinier-Preston zone and T″ phase in the form of intragranular, fine, and spherical particles, while a semi-coherent T' phase appears after the FTMT process as a new constituent. The distribution of dislocation tangles and isolated dislocations is another feature of FTMT samples. Enhanced precipitation hardening and dislocation strengthening account for the improved mechanical performance of FTMT samples.

Novel two-stage aging treatment to enhance hardening of Zn-containing SiCp/6xxxAl composites

Microalloying Zn in 6xxxAl (Al–Mg–Si) alloys and their composites can hardly form precipitates during artificial aging (AA) at 170 °C, so exhibits weak hardening abilities. In this study, a low-temperature AA at 120 °C was introduced after 170 °C AA to exploit the hardening potential of Zn. A 17 vol.% silicon carbide particles (SiCp) reinforced Al-1.2Mg-0.6Si-1.0Zn (wt.%) composite was used to inspect the effectiveness of the two-stage AA process. It is shown that AA at 120 °C can further improve the hardness based on the highest hardness during 170 °C AA. The increase in hardness during AA at 120 °C is mainly attributed to the precipitation of Zn. Interestingly, Zn neither independently forms precipitates nor forms new phases. The precipitation form of Zn is to segregate into dislocation-induced and discrete precipitates formed during AA at 170 °C. This study is expected to provide new ideas to harden SiCp/6xxxAl composites by composition design and AA process control.

Effect of heat treatment process parameters on the microstructure and properties of GH4720Li superalloy

The solution temperature and aging temperature of GH4720Li superalloy are the critical factors in determining its microstructure stability and mechanical properties. However, the matching of solution temperature, primary aging temperature, and second aging temperature greatly influences the final microstructure and mechanical properties, and the mechanism was rarely studied. In this paper, the effects of solution temperature, aging temperature, and other process parameters on the grain size, precipitated phase, and mechanical properties of GH4720Li superalloy were systematically studied by orthogonal experiment, and a set of optimal heat treatment process parameters were found. The results show that the sample was solution treated in the temperature range of 1060 °C ∼ 1120 °C. When the solution temperature was 1160 °C ∼ 1100 °C, although the primary γ ′ phase gradually dissolved, the secondary γ ′ phase gradually increased, and the primary γ ′ phase was pinned at the grain boundary to hinder the grain growth, and the hardness of the alloy gradually increases. When the solution temperature exceeded 1100 °C, the primary γ ′ phase dissolved in large quantities, the grains grew up rapidly, and the hardness of the alloy decreased. The sample was subjected to two-stage aging treatment in the temperature range of 650 °C ∼ 770 °C and 760 °C ∼ 880 °C. As the aging temperature increased, the primary γ ′ phase of the sample gradually grew, and the ability to pin the grain boundary weakened. The volume fraction of the secondary γ ′ phase of the sample gradually decreased and coarsened, resulting in grain growth and a gradual decrease in the hardness of the sample. When the samples were treated by 1100 °C/OC × 4 h + 650°C /AC × 8 h + 760 °C/AC × 8 h, the grain size of the sample was the smallest, the average grain size was 4.5 μm, the distribution of γ ′ phase was the most uniform, and the mechanical properties are the best, reaching 47 HRC.

Strengthening effect of prefabrication (10–12) tensile twinning on AZ80+0.4%Ce magnesium alloy and inhibition mechanism of discontinuous precipitation

This paper provided an effective method to further improve the mechanical properties of the AZ80+0.4%Ce magnesium alloy wheel spoke. The effect of high strength and ductility was obtained with a yield strength of 295.36 MPa, an elongation of 10%, by the combination of pre-deformation (7% deformation) and two-stage aging treatment (120 °C/9 h + 175 °C/24 h). The evolution of the microstructure and properties of the alloy was explored under the coupling conditions of different pre-deformation degrees and multi-stage aging. The results show that, pre-deformation introduced a large number of (101¯2) tensile twinning and dislocations, which greatly promoted the probability of continuous precipitates (CPs) appearing. On the contrary, the discontinuous precipitates (DPs) were limited by the vertical and horizontal twin structure. As a result, the pre-nucleation method of two-stage aging increased the proportion of CPs by 34%-38%. Owing to the DPs was effectively suppressed, the alloy's yield strength has been greatly improved. Besides, under multi-stage aging, the twin boundaries induce protruding nucleation to form static recrystallization by hindering the migration of dislocations, and the matrix swallows the twins, then the texture gradually tilts from the two poles to the basal plane. As an important supplement, the grain refinement and oblique texture promoted the improvement of the yield strength of the component.

Optimizing strength and electrical conductivity of Cu-Cr-Zr alloy by two-stage aging treatment

Cu-Cr-Zr alloy can be strengthened by modulating the aging process. In this work, the effect of two-stage aging on the properties of Cu-Cr-Zr solid solution was studied. Hardness, tensile properties and electrical properties were tested, and the microstructures were examined by transmission electron microscope. The results show that pre-aging can facilitate the formation of GP zones in the matrix, and thus accelerate the precipitation of high-density nano-sized phase in a shorter time as compared to that in the one-stage aging process. The two-stage aging route harmonizes the strength, ductility and electrical conductivity of the alloy, and provides an accessible strategy to ameliorate the comprehensive properties of the Cu-Cr-Zr alloy.

Enhancing the properties of Al–Ni added medium Mn steel by tailoring B2–NiAl precipitates through aging treatment

In the present work, the effect of aging treatment and the role of precipitates in improving the strength-ductility combination of intercritically annealed Fe–8Mn–4Al-3.5Ni-0.6Si-0.2C (wt.%) medium Mn steel has been studied. The steel has been intercritically annealed at 750 °C for 1 h and subjected to two different aging treatments, one-stage aging treatment at 500 °C for 3 h, and two-stage aging comprising first stage at 650 °C for 3 h followed by water quenching and second stage at 500 °C for 3 h. The microstructure, precipitates characteristics, mechanical properties and deformation behavior of the aged samples have been investigated. It was observed that after one-stage and two-stage aging treatment, the strength-ductility product of the steel improved significantly. The one-stage aging led to the formation of nano-sized NiAl precipitates in both ferrite and austenite, which resulted in an increment of yield strength (YS) by 300 MPa, with no notable decrease in ductility, as compared to the intercritically annealed sample. The two-stage aging led to phase-selective precipitation of NiAl of varying sizes in ferrite and austenite during the first and second stages of aging respectively. A combination of TRIP-TWIP effect and precipitation strengthening by the NiAl in austenite phase was observed in the two-stage aged sample, which led to sustained three-stage work-hardening during deformation resulting in improved elongation and strength-ductility combination.

Microstructure Evolution and Mechanical Properties of As-Cast and As-Compressed ZM6 Magnesium Alloys during the Two-Stage Aging Treatment Process.

In the present study, different solid solution and aging processes of as-cast and as-compressed ZM6 (Mg2.6Nd0.4Zn0.4Zr) alloy were designed, and the microstructure and precipitation strengthening mechanisms were discussed. After the pre-aging treatment, a large amount of G.P. zones formed in the α-Mg matrix over the course of the subsequent secondary G.P. prescription, where the fine and dispersed Mg12(Nd,Zn) phases were precipitated at the grain boundaries. The pre-aging and secondary aging processes resulted in the Mg12(Nd,Zn) phase becoming globular, preventing grain boundary sliding and decreasing grain boundary diffusion. Meanwhile, precipitation phase â″(Mg3Nd) demonstrated a coherent relationship with the α-Mg matrix after the pre-aging process, and after the secondary aging phase, Mg12Nd increases and became semi-coherent in the matrix. Compared to an as-cast ZM6 alloy, the yield strength of the as-compressed ZM6 alloy increased sharply due to an increase in the yield strength that was proportional to the particle spacing, where the dislocation bypassed the second phase particle. Compared to the single-stage aging process, the two-stage aging process greatly improved the mechanical properties of both the as-cast and as-compressed ZM6 alloys. The difference between the as-cast and as-compressed states is that an as-compressed ZM6 alloy with more dislocations and twins has more dispersed precipitates in the G.P. zones after secondary aging, meaning that it is greatly strengthened after the two-stage aging treatment process.

ICME guided design of heat-treatable Zn-modified Al–Mg alloys

Currently, there is a tendency towards breaking through conventional 5000 series aluminum alloys framework and designing heat-treatable Al–Mg based alloys with the improved mechanical properties. Here, based on a small amount of experimental work and our previously developed Integrated Computational Materials Engineering (ICME) framework, the authors systematically and efficiently optimize the Zn content and two-step aging treatment process in the heat-treatable Al–Mg–Zn alloys. It is found that the addition of 3.0 wt.% Zn can lower the nucleation activation energy, promote the precipitation of the T phase, and thus enhance and accelerate the age-hardening response of Al–Mg–Zn alloys. Different from the single-step aging process, the pre-aging treatment leads to a large number of fine and dispersive T precipitates due to the precipitation of numerous, stable and dispersive precursors. Further, we optimized two-stage aging treatment for the Al-5.1Mg-3.0Zn alloy which enables the peak-aged yield strength to increase by 21.1% as compared to that in the single-step aging process. This research presents an efficient strategy to design new-generation aluminum alloys via combining the key experimental data and an ICME framework.

Interaction of stress relaxation aging behavior and microstructural evolution in Inconel 718 alloy with different initial stress status

The two-stage aging treatment with different initial loading stresses were carried out in the Inconel 718 alloy after solution annealing process to investigate the stress relaxation and age hardening behaviors on basis of microstructural evolution. The result showed that the stress relaxation behavior mainly occurred in the first aging stage and the corresponding mechanism changed from diffusion creep with initial loading stress of 100 MPa into dislocation slip with initial stress of 600 MPa. Simultaneously, the influence of initial stress on yield strength was counteracted balanced the creep recovery and dislocation hardening, resulting in nearly constant value if yield strength. During the secondary aging stage, the strength of the purely aged sample is 3% higher than that of the high initial stress sample, and the precipitated phase morphology distribution is more uniform. The stress relaxation occurred in the secondary aging stage was negligible, irrespective of initial stress status. In condition, the application of initial stress gave rise to the precipitation behavior, which presented faster growth and coarsening with increasing initial stress value. As a comparison, the distribution of precipitates in sample without loading stress relatively more homogeneous and revealed denser, leading to higher yield strength compared with other samples with initial stress.

Influence of Isothermal ω Transitional Phase-Assisted Phase Transition From β to α on Room-Temperature Mechanical Performance of a Meta-Stable β Titanium Alloy Ti-10Mo-6Zr-4Sn-3Nb (Ti-B12) for Medical Application.

The microstructural evolution and tensile performance of a meta-stable β-type biomedical Ti−10Mo−6Zr−4Sn−3Nb (Ti-B12) alloy subjected to one-stage aging (OSA) and two-stage aging (TSA) are investigated in this work. The OSA treatment is performed at 510°C for 8 h. The TSA treatments are composed of low-temperature aging and high-temperature aging. In the first step, low-temperature aging is conducted at 325°C for 2 h. In the second step, the aging temperature is the same as that in the OSA. The result of the microstructure evolution shows that the precipitated secondary phase after aging is mainly influenced by the process of phase transition. There is a marked difference in the microstructure of the Ti-B12 alloy subjected to the OSA and TSA treatments. The needle-shaped α phases are precipitated in the parent β phase after the OSA treatment. Conversely, the short shuttle-like α phases precipitated after the TSA treatment are formed in the β matrix with the aid of the role of the isothermal ω transitional phase-assisted phase transition. The electron backscattered diffraction results indicate that the crystallographic orientation relationship of the α phases precipitated during the TSA treatment is basically analogous to those in the OSA treatment. The relatively higher tensile strength of 1,275 MPa is achieved by strengthening the effect of the short shuttle-like α precipitation with a size of 0.123 μm in length during the TSA treatment, associating with a suitable elongation of 12% at room temperature simultaneously. The fracture surfaces of the samples after the OSA and TSA treatments indicate that preventing the coarsening of the α layers in the grain boundaries is favorable for the enhancement of strength of Ti-B12 at room temperature. MTT test was carried out to evaluate the acute cytotoxicity and biocompatibility of the implanted material using L929 cells. The relative proliferation rates of cytotoxicity levels 0, 1, 2, 3, and 4 are ≥100, 80–99, 50–79, 30–49, and 0–29%, respectively. The cytotoxicity of the Ti-B12 alloy is slightly better than that of the Ti−6Al−4V alloy, which can meet the requirements of medical materials for biomedical materials.

Microstructure of Al-5Cu-1Li-0.6Mg-0.5Ag-0.5Mn Alloys

Microstructural optimization of Al-Li alloys plays a key role in the adjustment of mechanical properties as well as corrosion behavior. In this work, Al-5Cu-1Li-0.6Mg-0.5Ag-0.5Mn alloy was homogenized at different temperatures and holding times, followed by aging treatment. The microstructure and composition of the homogenized alloys and aged alloys were investigated. There were Al7Cu4Li phase, Al3Li phase, and Al2CuLi phases in the homogenized alloys. The Al7Cu4Li phase was dissolved with an increase in homogenization temperature and holding time. Al2Cu phase and Al2CuLi phase coarsened during the homogenization process. The alloy homogenized at 515 °C for 20 h was subjected to a two-stage aging treatment. Peak-age alloy, which had gone through age treatment at 120 °C for 4 h and 180 °C for 6 h, was mainly composed of α-Al, Al20Cu2Mn3, Al2CuLi, Al2Cu, and Al3Li phases. Tafel polarization of the peak-age alloys revealed the corrosion potential and corrosion current density to be −779 mV and 2.979 μA/cm2, respectively. The over-age alloy had a more positive corrosion potential of −658 mV but presented a higher corrosion current of 6.929 μA/cm2.

Obtaining Ultra-High Strength and Ductility in a Mg–Gd–Er–Zn–Zr Alloy via Extrusion, Pre-deformation and Two-Stage Aging

The Mg–12Gd–1Er–1Zn–0.9Zr (wt%) alloy with ultra-high strength and ductility was developed via hot extrusion combined with pre-deformation and two-stage aging treatment. The age-hardening behavior and microstructure evolution were investigated. Pre-deformation introduced a large number of dislocations, resulting in strain hardening and higher precipitation strengthening in the subsequent two-stage aging. As a result, the alloy showed a superior strength–ductility balance with a yield strength of 506 MPa, an ultimate tensile strength of 549 MPa and an elongation of 8.2% at room temperature. The finer and denser β′ precipitates significantly enhanced the strength, and the bimodal structure, small β-Mg5RE phase as well as dense γ′ precipitates ensured the good ductility of the alloy. It is suggested that the combination of pre-deformation and two-stage aging treatment is an effective method to further improve the mechanical properties of wrought Mg alloys.

Microstructure, precipitates and mechanical properties of Inconel 718 alloy produced by two-stage cold rolling method

In order to improve the mechanical properties of Inconel 718 alloy, two-stage cold rolling method was applied, which involved primary cold rolling, intermediate annealing, secondary cold rolling and aging treatment. A large number of short rod-shaped and spherical δ particles precipitated on grain boundaries, which could effectively improve the plasticity of Inconel 718 alloy. Subsequent secondary cold rolling and two-stage aging treatment improved the strength of the material through the combined effects of work hardening and precipitation of γ'' + γ′ strengthening phases. The aged samples after secondary cold rolling exhibited an excellent combination of yield strength (~ 945 MPa), ultimate tensile strength (~ 1080 MPa), and total elongation (~ 36%) when deformed at 650 °C. And its ultimate tensile strength at room temperature is ~ 1500 MPa. These excellent mechanical properties can be attributed to the proper fraction of δ phase precipitates, together with optimal morphology of δ phase.

Study on properties and microstructure of an Al–Cu–Mg–Fe–Ni alloy with two-stage aging treatment

The Al–Cu–Mg–Fe–Ni alloy has good high temperature properties, and it can be improved by two-stage aging heat treatment. Through Taguchi method to design experimental and analysis are carried out, determine the best experimental condition. At present, the hardness and tensile strength of the alloy as an optimized targets. The four influence factors of first-stage aging temperature, first-stage aging time, second-stage aging temperature and second-stage aging time as the optimization conditions. The hardness and tensile properties of the alloy are tested. The results show that the best two-stage aging heat treatment process is the first-stage aging condition of 180 °C for 8 h and the second-stage aging condition of 240 °C for 6 h. The tensile strength of the alloy at high temperature is improved the 30 MPa up and down.

Microstructure and Hardness Evolution in Haynes 282 Nickel-Based Superalloy During Multi-variant Aging Heat Treatment

In this paper, the effect of applied multi-variant heat treatment on microstructure, phase composition and mechanical response of Haynes 282 nickel-based superalloy was investigated. For this reason, temperatures of both stages of standard two-stage aging treatment (i.e., 1010 °C/2 h + 780 °C/8 h) were extended to 900-1100 °C/2 h and 680-880 °C/8 h ranges, respectively. Consequently, 30 different variants of heat treatment were applied. The microstructural features of heat-treated samples were investigated by means of light microscopy and SEM/EDS methods, while mechanical properties were examined via microhardness measurements. It was found that by using various combinations of temperatures of the first and second stage of aging, the room temperature hardness of Haynes 282 alloy can be decreased by ~ 100 HV units or increased by up to 25 HV units as compared to that of the alloy subjected to the standard heat treatment schedule. The mechanical response of the alloy is determined by a complex structural evolution involving the secondary precipitation of γ′, M23C6 and M6C phases, as well as their interaction with the fcc γ matrix.

Effect of minor additions on the microstructures and stress rupture properties of a directionally solidified Ni-based superalloy

The effects of C, Zr and Y/Ce on the microstructures and stress rupture properties of a directionally solidified Ni-based superalloys were investigated. The morphology of MC carbides does not change in as-cast alloys, as the C content is increased or the Zr is added. However, the Y/Ce additions promote the transformation of MC carbide morphology from blocky to script-like type. Compared with that in as-cast alloys, there is no obvious change in the morphologies of MC carbide or chemical compositions after heat treatment. The increasing of C content and the addition of Zr or Y/Ce significantly decreases and increases the amount of the γ/γ′ eutectic, respectively. After a solid solution treatment and subsequently a two-stage aging treatment, the γ′ phase is characteristic with two kinds of shapes and sizes, and the volume fraction of cuboidal γ′ phase is much larger than that of spherical γ′ phases. More MC carbide and residual eutectic result from the decreasing of cuboidal γ′ phase volume fraction. The decrease in volume fraction of cuboidal γ′ phase is principally responsible for the reduction of the stress rupture property. In addition, script-like carbide and residual eutectic remaining after heat treatment play the secondary role in the degradation of the stress rupture properties. The less regularly arranged cuboidal γ′ phase can damage the stress rupture life to some extent. The spherical γ′ phase re-dissolves into γ′ matrix widening the spacing between large cuboidal γ′ phase, and the addition of Zr inhibits grain boundary sliding and cracking; these two facts are beneficial to the rupture elongation.