Two-step Aging Research Articles

Microstructures and properties of 2099 Al-Li alloy

In this study, microstructures and properties of 2099 Al-Li alloy were investigated during the thermo-mechanical processing. Treated by two-step homogenization treatment (12 h at 510°C+36 h at 530°C), the coarse dendritic structures cannot be observed in the alloy. At the same time, the level of grain boundary segregation was lowered, and a few of small AlCuFeMn/AlCuMn particles remained at the grain boundaries. Following homogenization treatment, the alloy was extruded at 470°C. During extrusion process, dynamic recrystallization occurred in the surface layer of alloy, and the depth of dynamic recrystallized layer increased with solution treating at 540°C. The central zone of alloy with solution treatment exhibited {111}<112> and {111}<110> textures, while {112}<110> texture presented at the surface zone. The corresponding central hardness of alloy in central zone was 95 HV, and the surface hardness was 120 HV. After solution treatment, two-step aging treatment was followed. In the peak-aged condition (12 h at 121°C+48 h at 152°C), a large amount of T1 phases as well as δ′ phases precipitated in the matrix. The tensile strength, yield strength and elongation of alloy on peak aging were 613MPa, 575MPa, and 7.9%, respectively. The SCC susceptibility of alloy decreased with aging time, and the strength loss rate of alloy on over-aging was 5.5%.

Experimental Study on Heat Yreatment Processing of a New Low Cost Titanium Alloy Used in Aviation Field

The effect of common solution treatment, two-step solution treatment and aging, solution treatment and aging (STA) on the microstructure and mechanical properties of a new low cost titanium alloy used in aviation field were investigated by optical microscope (OM), scanning electron microscopy (SEM) and tensile test. The results show that a typical equiaxed structure can be obtained by common solution treatment leading to a good combination of strength and plasticity. Besides, solution heat treating in the β region and subsequently ageing at a low temperature results in a significant increase in mechanical strength and a little decrease in plasticity. When the solution temperature is at α+β two-phase region (895), the low cost titanium alloy acquires the best combination of strength and ductility.

A high strength and ductility Mg–Zn–Al–Cu–Mn magnesium alloy

A high strength Mg–8.0Zn–1.0Al–0.5Cu–0.5Mn(wt.%) magnesium alloy with outstanding ductility was developed using a common casting technique and heat treatment. The microstructure of the as-cast alloy is composed of α-Mg, MgZn, MgZnCu and Al–Mn phases. After the solution treatment and subsequent two-step aging treatment, the yield strength (YS), ultimate tensile strength (UTS) and elongation of the alloy at peak hardness reach 228MPa, 328MPa and 16.0% at room temperature, respectively. The comprehensive mechanical properties of the alloy are superior to almost all other high performance casting Mg alloys.

Effects of Cu and Ag additions on age-hardening behavior during multi-step aging in AlMgSi alloys

Low Cu and Ag additions (≤0.10at%) were found to strongly affect the age-hardening behavior in AlMgSi alloys with Mg+Si>1.5at%. The hardness increased during aging at 170°C and the formation of β″ precipitates was kinetically accelerated. The activation energy of the formation of the β″ phase was calculated to 127, 105, 108 and 99KJmol−1 in the base, Cu-added, Ag-added and CuAg-added alloys, respectively using the Kissinger method. The negative effect of two-step aging caused by the formation of Cluster (1) during natural aging was not overcome by the addition of microalloying elements. However, it was suppressed by the formation of Cluster (2) through a pre-aging at 100°C. Quantitative analysis of the precipitate microstructure was performed using a transmission electron microscope equipped with a parallel electron energy loss spectrometer for the determination of specimen thickness. The formation of Cluster (2) was found to increase the number density of β″ precipitates, whereas the formation of Cluster (1) decreased the number density and increased the needle length. The effects of low Cu and Ag additions in combination with multi-step aging are discussed based on microstructure observations and hardness and resistivity measurements.

Effect of quenching rate on microstructure and mechanical properties of commercial AA7108 aluminium alloy

A commercial AA7108 aluminium alloy subjected to different quenching procedures from the solid solution temperature of 480 °C was considered. Both continuously cooling and quenching to intermediate temperatures (400, 300 and 200 °C) followed by different holding times were applied. All the materials were subsequently subjected to the same industrial two-step artificial ageing procedure to obtain a maximum strength (T6). Tensile testing of the different quenched materials in the T6 temper reveals a large deviation in strength dependent on the cooling/holding time, compared with the reference sample. A collection of the different quenched materials was chosen for further investigation of the precipitate structure by transmission electron microscopy (TEM) to explain the differences in mechanical properties.

Comparison of Mechanical Properties of RE-7075 Al Alloy's Hot Rolled Sheet and Cold Rolled Sheet

The experiment has studied the mechanical properties effect of rare earth(RE)-7075 Al alloy＇s hot rolled sheet and cold rolled sheet coursing by two-step aging treatment. The hot rolled sheet and cold rolled sheet were analyzed by EDS(energy dispersive spectrometer), SEM(scanning electron microscope) and tested by Brinell Hardness tester, Computer-controlled electronic universal testing. The results shows that the synthetical mechanical properties of hot rolled sheet exceeds cold rolled sheet. The tensile strength is higher approximately 80MPa, elongation is larger approximately 3% and Brill hardness is bigger approximately 30HB after the two-step aging treatment.

Effects of Microstructures on Fatigue Behavior of an Al-Mg-Sc Alloy at an Elevated Temperature

Polycrystalline Al-1wt%Mg-0.27wt%Sc alloys bearing Al3Sc particles with different average sizes of 4 and 11nm in diameter have been cyclically deformed at 423K under various constant stress amplitudes, and the relationship between fatigue characteristics and microstructure of the alloy has been investigated. The specimen bearing 11 nm particles exhibited a cyclic hardening to saturation, while in specimens with the small particles a cyclic softening was observed after initial hardening. In the specimen with large particles, dislocations were uniformly distributed under all applied stress amplitudes, whereas the specimens bearing small particles, in which cyclic softening occurred exhibited clearly developed slip bands. The cyclic softening for the latter specimen was explained by particle shearing within the strongly strained slip bands. The width of precipitate free zones (PFZs) has been found to be one of the factors affecting the fatigue life of the specimens at 423K. The two-step aging decreases the width of PFZs, resulting in increase in the fatigue life.

Influence of aging heat treatment on microstructure and hardness of single crystal Ni3Al-base superalloy IC21

The influence of high-temperature aging heat treatment on microstructure and hardness of single crystal Ni3Al-base superalloy IC21 were investigated. The results showed that the temperature and time of aging treatment had significant effect on the shape and the average size of γ’ precipitate as well as the hardness of the alloy. The average size and volume fraction of γ’ precipitate after 1320°C/10h/Ar cooling+870°C/32h/air cooling(AC) treatment were about 270nm and 63% respectively. The experimental results showed that the two-step aging treatment following the solution treatment significantly influenced the size and volume fraction of γ’ phase, i.e., through the treatment of 1320°C/10h/Ar cooling +1060°C/2h/AC+870°C/32h/AC the moderate size (about 450nm) and volume fraction (about 70%) of cubic γ’ phase obtained and the hardness of the alloy reached the maximum value of about 370HV. However, with the increase of the aging temperature or time the size and the volume fraction of γ’ precipitate increased and the morphology of the γ’ precipitate gradually changed from cubic shape to rod shape. It has been found that after 1320°C/10h/Ar cooling +1120°C/2h/AC+870°C/32h/AC or 1320°C/10h/Ar cooling +1060°C/6h/AC+870°C/32h/AC treatment the morphology of the γ’ precipitates obviously changed from cubic shape to rod shape and the hardness of the alloy decreased significantly.

Microstructural evolution and aging behavior of cryorolled Al–4Zn–2Mg alloy

Abstract The effect of cryorolling on microstructural evolution and aging characteristics of an Al–4Zn–2Mg alloy is investigated using differential scanning calorimetry (DSC), transmission electron microscopy (TEM), electron back scattered diffraction (EBSD) and hardness measurements. The Al–4Zn–2Mg alloy in solutionized condition was cryorolled to achieve 70–90% deformation. The cryorolled samples were short annealed followed by three different aging treatments viz., natural aging, peak aging and over aging. The EBSD results suggest the presence of ultrafine grains in the cryorolled alloy. DSC thermograms and aging studies revealed that cryorolling enhances the aging kinetics of the alloy. The two-step peak aging treatment indicated that the degree of peak hardness is directly proportional to the extent of deformation and the time to attain it varied inversely with respect to the amount of deformation. TEM studies of cryorolled and peak aged (CRPA) samples showed large number of uniformly distributed, finer and closely spaced η′ strengthening precipitates when compared to bigger precipitates in coarse grain peak aged (CGPA) alloy. Variations in precipitate distribution and morphology between CRPA and CGPA alloys are attributed to the stored energy and high density of dislocations generated during cryorolling.

Microstructure and Properties of a Hot Rolled-Quenched Cu-Cr-Zr-Mg-Si Alloy

The microstructure and properties of a hot rolled-quenched Cu-Cr-Zr-Mg-Si alloy were investigated by transmission electron microscopy observations, micro-hardness and tensile strength testing, and electrical conductivity measurement. The results show that the hot rolling-quenching (HR-Q) process and subsequent thermomechanical treatments are successfully developed to manufacture Cu-Cr-Zr-Mg-Si alloy strips. Solution treatment can be finished during the HR-Q process, and good combinations of strength, conductivity, and softening resistance are obtained for the thermomechanically treated strips. Ordered fcc structure precipitates which exhibit a cube-on-cube orientation relationship with the matrix are responsible for the improvements of properties. The properties of hot rolled-quenched Cu-Cr-Zr-Mg-Si alloy strips can be further improved by two-step rolling and aging process. The improvements of properties are attributed to the interactions of precipitation strengthening and strain hardening.

Effects of Solution and Two-Stage Ageing Treatment Process on Microstructure and Properties of 6061 Aluminum Alloy

Comprehensive performance of 6061 aluminum alloy was improved by solution treatment and two-step ageing treatment in this paper . The effects of different thermal processing parameters on the microstructure and mechanical properties of 6061 aluminum alloy were studied. The experimental results show that the optimal process of solution treatment for 6061 aluminum alloy is heated at 500°C for 10min. After first-stage aging, the hardness measurements and microstructure analysis results show that the hardness increased with increasing aging temperature, and reached peak value at temperature 180°C for 10h, while in the second-stage ageing treatment, the sample got the ageing peak value at 220°C for 1h. After two-stage treatment, the grains of 6061 aluminum alloy became uniform and fine and the second phase distributed along the grain boundary and play an important role of dispersion strengthening. Above all, the optimal heat treatment process of 6061 aluminum alloy is solution treated at 500°C for 10min, as well as ageing at 180°C, 10h and 220°C, 1h

The Study on Microstructure and Properties of a New Metastable Beta Titanium Alloy after Aging Treatment

New metastable beta titanium alloy Ti-4Al-2.7V-12Mo-10Nb-1Zr-0.2Cr was carried out in the arc melting vacuum furnace. The microstructure and mechanical properties of a new metastable beta titanium alloy Ti-4Al-2.7V-12Mo-10Nb-1Zr-0.2Cr were compared at different aging temperature and time. The growth mechanism of α phase is analysed by comparing the morphology of the precipitated phase at different temperature. Test results indicate that titanium alloy Ti-4Al-2.7V-12Mo-10Nb-1Zr-0.2Cr has the best property through two-step aging treatment. The tensile strength of titanium alloy Ti-4Al-2.7V-12Mo-10Nb-1Zr-0.2Cr after final aging treatment achieves 1180MPa with 8% elongation trough tensile test. The strengthing mechanism was also discussed in this paper.

수용액 합성법의 2단계 성장온도 변화를 통한 ZnO 결정의 선택적 용해 현상

ZnO hexagonal rods grown in aqueous solution can be changed into a tubular shape by two-step aging in the course of the growing process. In the first step, hexagonal ZnO rods is grown by aging at 90℃ under a highly supersaturated aqueous solution giving rise to a fast precipitation rate. Meanwhile, during the second step aging at 60℃ in the same aqueous solution, the hexagonal polar face (001) having higher surface energy than (010) side planes dissolves to minimize surface energy. Hence the flat (001) face changes to a craterlike face and the hexagonal rod length of ZnO decreases at an initial-stage of this step aging. The formation of the (101) wedge-type faces is ascribed to the resultant of competitive reactions between the dissolution of polar face minimizing the surface energy which is a dominant reaction at the initial stage and the precipitation reaction dissipating supersaturation. At a later stage of the second-step the reaction rates of these two processes in the aqueous solution become similar and the overall reaction is terminated.

Morphology and chemical composition of γ/γ' phases in Re-containing Ni-based single crystal superalloy during two-step aging

The γ/γ' microstructure of a Re-containing Ni-based single crystal super alloy after a two-step aging was studied using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). The crystals were grown by the floating zone (FZ) method. Both cuboidal and spherical γ' precipitates were formed after a two-step aging. The size of the cuboidal γ' phases first increased and then decreased with the extension of the second-step aging time. Re, Co and Cr strongly concentrated in the γ phase whereas Ni and Al enriched in the γ' phase. Thermodynamic calculation by JMatPro was performed to explain the experimental observations.

Heat treatment method for making high strength and conductivity Cu–Cr–Zr alloy

In this paper, the heat treatment called ‘a two-step aging process’ with the feature of the first step aging at a low temperature for a long time and the second step aging at a higher temperature for a short time has been proposed. Applying this process, the Cu–Cr–Zr alloy possessing both high strength and high conductivity can be acquired due to the formation of numerous tiny particles precipitated fully out from Cu matrix.

Effects of Ce addition on microstructure and mechanical properties of Mg-6Zn-1Mn alloy

The effects of Ce addition on the microstructure of Mg-6Zn-1Mn alloy during casting, homogenization, hot extrusion, T4, T6 and T4+two-step aging were investigated. The mechanical properties of alloys with and without Ce were compared. The results showed that Ce had an obvious effect on the microstructure of ZM61-0.5Ce alloy by restricting the occurrence of dynamic recrystallization and restraining the grain growth during extrusion and heat treatment subsequently. A new binary phase Mg 12Ce was identified in ZM61-0.5Ce alloy, which distributed at grain boundaries and was broken to small particles distributed at grain boundaries along extrusion direction during extrusion. The mechanical properties of as-extruded ZM61-0.5Ce alloy were improved with the addition of Ce. The improved tensile properties of as-extruded ZM61-0.5Ce alloy were due to the finer grain sizes as compared to ZM61 alloy. However, the UTS and YS decreased severely and the elongation increased when ZM61-0.5Ce was treated by T6 and T4+two-step aging. Brittle Mg 12Ce phase, which was distributed at the grain boundary areas and cannot dissolve into the Mg matrix after solution treatment, became crack source under tensile stress.

Effects of Two-Step Aging Temperature on Exfoliation Corrosion of an Al-Zn-Mg-Cu Alloy

The effects of two-step aging temperature on exfoliation corrosion of an Al-Zn-Mg-Cu alloy were characterized by EXCO test, electrochemical test and TEM observations. Results suggested that the partial recrystallized structure is susceptible to exfoliation corrosion which is greatly influenced by intergranular corrosion. The transfer current of the sample aged at 170°C (second-step aging temperature) is higher than that of the sample aged at 155°C. The second-step aging temperature exhibits more contributation to the exfoliation corrosion in this investigation, compared to the first-step aging temperature.

The Effect of Two-Step Aging on the Electrical Properties of 7075 Aluminum Alloy

This experiment has taken a research on the conductivity changes of 7075 aluminum alloy after being extruded and two-step aging treatment,and has done a analysis on the theory and rules of the impact on conductivity performance under the two-step aging treatment.Compared to cast aluminum alloy and extruded aluminum alloy without two-step aging process,the experiment showed that extruded alloy with two-step aging treatment has the highest conductivity about 44% IACS, 33.3% more than under casting condition and 22.2% more than only being extruded.

Effect of Two-Step Deforming and Aging Process on the Properties and Microstructure of Cu-Cr-Zr-Mg-Si Alloy

Effect of two-step deforming and aging process on the properties and structure of Cu-Cr-Zr-Mg-Si alloy was investigated. The results show under the condition of same cold deformation, two-step deforming and aging processes can improve overall performance of the alloy. The hardness obtained by two-step deforming and aging process is higher 6%-9% than that by single-step deforming and aging. The hardness and conductivity are up to 160HV and 88.1% IACS respectively after 80 % rolling and reaging at 480°C for 30min. The particles precipitate along the dislocation and pin on the dislocation during the reaging. These finer particles distribute more uniformly in the copper matrix and result in the higher strength and electrical conductivity.

Influence of HIP processing on microstructure and mechanical properties of superalloy Udimet 720LI

Inert gas (high purity argon) atomised powder of composition conforming to that of the superalloy Udimet 720 of low interstitial grade was hipped at 1200°C/120 MPa/3 h. The hipped alloy has shown near theoretical density and consisted of equiaxed grains with an average diameter of ∼45 μm. While primary γ′-Ni3 (Ti, Al) precipitates with an acicular morphology were found at the grain boundaries, finer secondary γ′ precipitates with near cuboidal morphology were present in the austenite γ matrix. The yield strength (YS) of the as hipped alloy was found to be the same as that of the wrought alloy heat treated for creep applications (termed as creep resistant alloy) at room temperature (RT) as well as at 650°C. However, the ultimate tensile strength (UTS) and ductility were found to be higher than those of the wrought creep resistant alloy. On the other hand, the YS and UTS of the as hipped material were lower than those of the wrought alloy heat treated for high strength applications (termed as high strength alloy), although the ductility of the former was comparable to that of the latter. In order to improve the strength, the hipped alloy was subjected to a heat treatment consisting of solution treatment followed by two-step aging. Extensive precipitation of fine and coarse γ′ precipitates with cuboidal morphology during duplex aging treatment has led to a considerable improvement in YS and UTS of the alloy, although the corresponding ductility dropped moderately at RT and at 650°C. Fractography of the tensile tested specimens has shown ductile transgranular mode of fracture in the as hipped alloy at RT and at 650°C, while the hipped+heat treated alloy exhibited a mixed mode of fracture at those temperature. The stress rupture properties of the as hipped alloy compare well with those of the wrought alloy and have been found to improve significantly after heat treatment. The present investigation reveals that the hipped superalloy Udimet 720LI has substantial potential for use in the development of near net shaped components for aerospace applications.