Effect of aging treatment on the precipitation transformation and age hardening of Mg-Gd-Y-Zn-Zr alloy

In this study, the precipitation transformation and age hardening of solution-treated Mg-9Gd-4Y-2Zn-0.5Zr(wt.%) alloy were investigated at different aging treatment parameters. The precipitation sequences of the alloy aged at 200℃, 250℃ and 300℃ are β’’(DO19) → β’(BCO) → β(FCC), β’’(DO19) → β’(BCO) → β_(1)(FCC) → β(FCC) and β(FCC), respectively. The streaks sequences of the alloy aged at 200℃, 250℃ and 300℃ are SF, SF → 14H-LPSO and SF → 14H-LPSO, respectively. For the alloy aged at 200℃ and 250℃, the increase in hardness with increasing aging time is contributed from the increase in precipitate volume fraction and the transformation from β’’ to β’ phase with basal → prismatic and spherical → spindle-like precipitate changes. The decrease in hardness after the peak-aging stage is attributed to the appearance of micro-sized β precipitates. Because of the smaller size of precipitates and the triangular arrangement of β’ precipitate, the hardness of the alloy aged at 200℃ is higher than that aged at 250℃. For the alloy aged at 300℃, the appearance of only micro-sized β precipitate and its coarsening with increasing aging time leads to the lowest hardness and an overall decrease in hardness with the aging time.

Effects of aging treatment processes on microstructures and mechanical properties of AZ63 casting magnesium alloy

The effects of three different aging treatment processes,namely single-stage,double-stage,and reverse double-stage aging treatment processes,on the microstructures and mechanical properties of the AZ63(Mg-6Al-3Zn-0.25Mn)casting magnesium alloy were investigated and compared.The results indicate that the microstructures of all the aged alloys under the three treatment processes are mainly composed ofα-Mg,Mg17Al12),and Al4Mn phases,indicating that the double-stage and reverse double-stage aging treatments have no obvious effect on the type of alloy phases.However,as compared with the single-stage and double-stage processes,the reverse double-stage process has a great effect on the quantity of the Mg17Al12phases.After the reverse double-stage aging treatment,which results in a stronger drive for decomposition of the supersaturated solid solution,the number of Mg17Al12phases precipitated in the grains significantly increases.In addition,as compared with the single-stage aged alloy,the tensile properties at room temperature for both the double-stage and reverse double-stage aged alloys are significantly improved.Among them,the reverse double-stage aged alloy achieves the highest tensile strength,yield strength,and elongation of 295 MPa,167 MPa,and 8.6%,respectively.

Influence of process parameters and aging treatment on the microstructure and mechanical properties of Al Si8Mg3 alloy fabricated by selective laser melting

Many studies have investigated the selective laser melting(SLM)of AlSi10Mg and AlSi7Mg alloys,but there are still lack of researches focused on Al-Si-Mg alloys specifically tailored for SLM.In this work,a novel high Mg-content AlSi8Mg3 alloy was specifically designed for SLM.The results showed that this new alloy exhibited excellent SLM processability with a lowest porosity of 0.07%.Massive lattice distortion led to a high Vickers hardness in samples fabricated at a high laser power due to the precipitation of Mg_(2)Si nanoparticles from theα-Al matrix induced by high-intensity intrinsic heat treatment during SLM.The maximum microhardness and compressive yield strength of the alloy reached HV(211±4)and(526±12)MPa,respectively.After aging treatment at 150℃,the maximum microhardness and compressive yield strength of the samples were further improved to HV(221±4)and(577±5)MPa,respectively.These values are higher than those of most known aluminum alloys fabricated by SLM.This paper provides a new idea for optimizing the mechanical properties of Al-Si-Mg alloys fabricated using SLM.

Effect of aging treatment on evolution of S'phase in rapid cold punched Al−Cu−Mg alloy

High-resolution transmission electron microscopy(TEM),X-ray diffractometer(XRD),and hardness test were used to study the evolution of long plate-shaped S'phase in the spray-formed fine-grained Al−Cu−Mg alloy during aging after rapid cold punching deformation.Results show that the long plate-shaped S'phase in the extruded Al−Cu−Mg alloy undergoes evident distortion,brittle failure,separation and redissolution,during rapid cold punching deformation,leading to the transformation of long plate-shaped S'phase into short rod or even redissolution and disappearance,causing the matrix to become a supersaturated solid solution.After the aging treatment,the reprecipitation of the phases occurs,and these aging phases are mainly long plate-shaped and granular.The incompletely dissolved S'phase acts as nucleation core,promoting uphill diffusion of the surrounding solute atoms.The S'phase gradually grows with increasing the aging time.The completely dissolved S'phase forms the incoherent equilibrium phase with the matrix to reduce its free energy.After rapid cold punching,the aging response of the deformed Al−Cu−Mg alloy is accelerated,and the hardness of the alloy is substantially increased.

Transformation behavior and shape memory effect of Ti_(50-x)Ni_(48)Fe_2Nb_x alloys by aging treatment

The influence of aging treatment on transformation behavior and shape memory of the Ti 50_x Ni_(48) Fe_2 Nb_x(x=0,0.6,0.8,1.0,and 1.2) alloys was investigated using differential scanning calorimeter(DSC),mechanical drawing machine,and microhardness tester in this paper.It is indicated that the aging treatment has a significant effect on the phase transformation temperatures(M_s,M_f,M_p,A_s,A_f,and A_p) and microhardness of the samples.The phase transformation temperatures are found to decrease initially with the increasing aging temperature from 300 to 500 ℃ and increase with further increase of the aging temperature.The aging treatment at intermediate temperature between 400 and 500 ℃ results in an improved shape memory effect.In addition,the highest microhardness value is also obtained.

Effects of Aging Treatment on Intergranular Corrosion and Stress Corrosion Cracking Behavior of AA7003

In order to study the effects of aging treatment on the intergranular corrosion（IGC） and stress corrosion cracking（SCC） of 7003 aluminum alloy（AA7003）, the intergranular corrosion test, electrochemical test and slow strain rate test（SSRT）, combined with optical microscopy（OM） and scanning electron microscopy（SEM） as well as transmission electron microscopy（TEM） observations have been carried out. The IGC and electrochemical test results showed that the IGC resistance of AA7003 for peak aged（PA） temper is the lowest, with double peak aged（DPA） the moderate, and retrogression and re-aging（RRA） the highest among three tempers, which is attributed to the continuous feature of precipitation on grain boundary of PA temper and the interrupted feature of precipitation on grain boundary of DPA and RRA tempers, as well as the wide precipitation free zones（PFZ） of RRA temper. In addition, the SSRT results indicated that all three tempers AA7003 are susceptible to SCC in IGC solution, and the change tendency of SCC susceptibility（ISCC） of AA7003 for three tempers follows the order： ISCC（RRA）

Effect of cryogenic and aging treatments on low-energy impact behaviour of Ti-6Al-4V alloy

The objective of this study is to examine the effects of cryogenic and aging treatments on the impact strength andmechanical properties of Ti?6Al?4V alloy.To accomplish that objective,cryogenic treatment(CT),aging treatment(AT)andcryogenic treatment followed by aging treatment(CAT)were conducted on Ti?6Al?4V alloy.Impact tests were performed onheat-treated and untreated samples using different impactor nose geometries(hemispherical,60°and90°conical)to determine theeffect of impactor nose geometry on the damage characteristic.The findings showed that energy absorption increased and areas ofdamage decreased as a result of heat treatment in all treated samples.The highest energy absorption was observed in the CATsamples,due to the increase in energy absorption,the smallest damaged area occurred in the CAT sample,and the largestdeformation was seen in the untreated samples.Additionally,it was seen that the damaged area and deflection were stronglydependent on impactor nose geometry.The maximum deflection and narrowest deformation area were seen with60o conical nosegeometry.The deformation area increased with increasing impactor nose angle.

Influence of aging treatment on corrosion behavior and mechanism of Mg–Y alloys

This paper studied the influence of aging treatment on the corrosion behavior and mechanism of Mg-Y alloys with different Y content through corrosion mass loss test, electrochemical test and corrosion morphologies observation. Results show that the peak-aging times of Mg-（0.25, 2.5, 5, 8 and 15） Y alloys at 250 ℃ were 4, 6, 10, 12 and 16 h. The aging treatment reduced the corrosion resistance of Mg-Y alloys, and the corrosion resistance of Mg-Y alloys became worse with increasing of the aging time. The change magnitude of the open circuit potentials for Mg-（0.25, 2.5）Y alloys was greater than that of Mg-（5, 8 and 15）-Y alloys. The polarization curves of Mg （0.25, 2.5, 5, 8 and 15） Y alloys had the similar shape after aging treatment, and the slopes of the anodic branch were greater than those of the cathodic branches. After aging treatment, the corrosion modes of Mg-0.25Y and Mg-（2.5, 5, 8 and 15） Y alloys were uniform corrosion and pitting corrosion with small local deep corrosion.

A New Aging Treatment Way for Near α High Temperature Titanium Alloys

Two near α titanium alloys, Ti-5.6Al-4.8Sn-2.0Zr-1Mo-0.35Si （1#） and Ti-6.0AI-4.8Sn-2.0Zr-1Mo-0.35Si （2#）, were solution-treated in the upper α＋β phase fields, and the duplex mixture microstructures consisting of the less volume fraction primary α phase （αp） and the transformed β phase （βt） were obtained. The aging treatments were carried out at 700℃ for 1# alloy and 760℃ for 2# alloy under varied terms, respectively. It guaranteed α2 ordered phase to precipitate only in αp but not in βt for the two alloys. The slower precipitation and growth of the α2 ordered phase and silicide was observed in 1# alloy in comparison with 2# alloy. The mechanical properties including tensile strength and ductility, the creep and lasting properties at 600℃ were investigated. Prolonging aging time did not predominantly change the tensile strength and ductility for the two alloys. The 600℃/100 h thermal exposure caused a notable decrease of tensile ductility in 2# alloy though no distinct decrease could be observed in 1# alloy after the thermal exposure. The lasting property of i# alloy was increased with prolonging aging time and finally was equal to or even better than that of 2# alloy. Nevertheless, no evident increase emerged in 2# alloy with prolonging aging time. Similarly, the creep property of 1# alloy monotonously increased with increasing aging time and finally was equal to or even better than that of 2# alloy. No evident increase could be observed for 2# alloy. It can be deduced that the overgrowth of α2 ordered phase and silicide is unable to enhance hot strength properties but cause an unacceptable damage to tensile ductility. The optimum equilibrium of the comprehensive properties depending on the proper control of α2 ordered phase and silicide can be achieved by properly selecting aging temperature and time.

Effect of optimal aging treatment on magnetic performance and mechanical properties of sintered Nd-Fe-B permanent magnets

The magnetic performance and mechanical properties including hardness, brittleness, fracture toughness and strength characteristics of the as-sintered and the optimal aged Nd-Fe-B magnets were examined in this work. A new method of Vickers hardness indentation combined with acoustic emission was used to test the brittleness of the magnets.The results show that the magnetic properties of the magnets could be improved through aging treatment, especially the intrinsic coercive force. But it is accompanied by a decrease of strength and fracture toughness. Theoretical calculation confirms that acoustic emission energy accumulated count value could be used to characterize the material brittleness. The bending fracture morphologies of the as-sintered and the optimal aged Nd Fe B magnets were investigated with the emphasis on the relationship between mechanical properties and microstructure using a field emission scanning electron microscopy(FE-SEM). The research results indicate that the intergranular fracture is the primary fracture mechanism for both as-sintered and optimal aged Nd Fe B magnets. Aging treatment changes the morphology and distribution of the Nd-rich phases, reducing the sliding resistance between Nd_2Fe_(14)B main crystal grains and lowers the grain boundary strength, which is the main reason for the strength and fracture toughness decrease of the aged Nd-Fe-B magnets.

Effect of Aging Treatment on Microstructural and Mechanical Characteristics of PEO Coatings on Mg-Al Alloy

Cast Mg-6 wt pct Al alloy solution-treated at 683 K for 16 h and aged at 498 K was coated by plasma electrolytic oxidation （PEO） method.The Mg-6 wt pct Al alloy aged for 16 h exhibited the highest microhardness and wear resistance.After PEO coating,however,the microhardness and wear resistance of coatings on Mg- 6 wt pct Al alloy showed a tendency to decrease with increasing aging time,which was in aggrement with the change of thickness with aging time.In addition,the coatings on solution-treated Mg-6 wt pct Al alloy had better microhardness and wear resistance than those on aged Mg-6 wt pct Al alloys.Consequently,it can be understood that the aging treatment has a deleterious influence on the mechanical properties of coatings on Mg-6 wt pct Al alloy.

Enhanced strengthening by two-step progressive solution and aging treatment in AM50-4%(Zn,Y) magnesium alloy

AM50-4%(Zn,Y)alloy with a Zn/Y mole ratio of6:1was subjected to thermal analysis,and the results were used for designing a two-step progressive solution treatment process.The effects of solution and aging treatments on the microstructure and mechanical properties of the AM50-4%(Zn,Y)alloy were investigated using OM,XRD,SEM/EDS,TEM,tensile test and hardness test.The experimental results demonstrated that the two-step progressive solution treatment could make theΦandβphases sufficiently dissolve into the matrix which possessed higher supersaturated degree of the dissolved solute compared with the one-step solution treatment.This resulted in a certain enhancement of the precipitation strengthening effect during the subsequent aging process.The precipitation of theФphase had a greater impact on the comprehensive mechanical properties of the alloy thanβphase precipitation when the aging treatment was performed at180℃.The peak aging strength of the AM50-4%(Zn,Y)alloy which was subjected to the two-step progressive solution treatment process(345℃for16h and375℃for6h)was obtained after the aging treatment at180℃for12h.

Optimal Selection and Control for Precipitation of α_2 Phase in Near α High Temperature Ti Alloys during Aging Treatment

The characteristic of the precipitation and growth of α2 ordered phase during aging treatment in near α Ti alloys have been investigated in terms of the influences of aging temperature, aging time and aging manner. The results exhibit that aging temperatures influence the distribution of α2 phase precipitated and cause the changes in growth speed of α2 phase. For various aging temperatures, the time to finish precipitation of α2 phase is different. The facts that various distribution characteristics and growth speed of α2 ordered phase are caused by changed aging condition imply optimal selection and control for precipitation of α2 ordered phase reachable. Some discussions on adoptable aging steps are presented.

Effect of Deformation and Aging Treatment on Electrical Conductivity of Cu-Cr Alloy

The effect of deformation and aging treatment on the electrical conductivity of Cu-Cr alloy was studied. The results show that deformation can reduce the electrical conductivity of Cu-Cr alloy, but deformation followed by optimum aging treatment can effectively improve the electrical conductivity of Cu-Cr alloy, under the condition of 0～70% deformation, and the electrical conductivity of Cu-Cr alloy by aging treatment increases and the aging time of obtaining much better electrical conductivity of Cu-Cr alloy decreases with increase in deformation quantity of Cu-Cr alloy. The best electrical conductivity of Cu-Cr alloy after deformation can be obtained by aging treatment at 500 ℃. And also the reasons for the variations of alloy's electrical conductivity and the function of adding RE were analyzed.

EFFECT OF PROGRESSIVE AGING TREATMENT ON THE PROPERTIES AND MICROSTRUCTURE OF THE HIGH-HARD ELASTIC NICKEL-CHROMIUM-ALUMINIUM ALLOY

A dispersion-hardened high-hard elastic alloy is developed by adding 3%/ of aluminium (Al) to the nickel-chromium alloy. The experimental results show that after a progressive aging of the alloy at 550℃ or 5 h, supersaturated Cr(α)-rich phase (80 wt% Cr)formed. The Cr content of this phase is by 40 wt% higher than that in as-prepared alloy. An analysis of quantitative metallography shows that the seperated Cr(α)-rich phase grains have an average size(D) of 1.8225 mm and the total area of the particles is 16. 7% of the measured area (Pa = 16.7%). The large amount of dispersively distributed supersaturated Cr(α)-rich phase which are seperated out during progressive aging process strengthen the alloy matrix, and raise the hardness and bending strength of the alloy.

Effects of pre-aging treatment on subsequent artificial aging characteristics of Al-3.95Cu-(1.32Mg)-0.52Mn-0.11Zr alloys

The effects of pre-aging treatments on subsequent artificial aging response were investigated by means of transmission electron microscopy observations and hardness test in age hardened Al-3.95Cu-(1.32Mg)-0.52Mn-0.11 Zr alloys. In Al-3.95Cu-0.52Mn-0.11 Zr alloy, when the pre-aging temperature is 25 °C, the pre-aging treatment has no evident effect on the peak hardness of subsequent artificial aging, while a positive effect(increase of peak hardness) appears when pre-aging temperature is50 °C. However, in Al-3.95Cu-1.32Mg-0.52Mn-0.11 Zr alloy, it is found that whether the pre-aging temperature is 25 °C or 50 °C,the peak artificial aging hardness is lower than that of T6 treated alloy, that is to say, pre-aging treatment has a negative effect on the peak hardness of subsequent artificial aging in the alloys.

Two-stage aging treatment to accelerate aging kinetics without impairing strength in B_4C/7A04Al composite

Aging treatments are the key process to obtain satisfactory strength for 7xxxAl alloys and their composites. However, traditional single-stage(SS) aging is time-consuming to reach a peak strength condition. In this study, an efficient 120℃ + 160℃ two-stage(TS) aging treatment was proposed on a B_4C/7A04Al composite fabricated via powder metallurgy(PM) technology, which could acquire similar peak-aging strength but only took about 15% of the time compared to traditional 120℃ SS aging. The evolution of precipitation during the TS aging was investigated, as well as those of the 7A04Al alloys for comparison. In the second stage aging process, the higher aging temperature accelerated the nucleation of η′ phases inside the grains and thus increased the density of precipitates. Moreover, the short aging time limited the coarsening of precipitates and the broadening of precipitatefree zones. The above factors were beneficial for quickly obtaining satisfactory precipitation strengthening effects. The B_4C/7A04Al composite exhibited slower aging kinetics than the 7A04Al alloy in the TS aging. Mg elements consumption by the chemical reaction between B impurities introduced by B_4C particles and the Al matrix was considered to potentially retard the aging kinetics of the B_4C/7A04Al composite. Nevertheless, the precipitation sequence was not affected.

Ultrahigh strength and improved electrical conductivity in an aging strengthened copper alloy processed by combination of equal channel angular pressing and thermomechanical treatment

In this paper,equal channel angular pressing and thermomechanical treatment was employed to improve the strength and electrical conductivity of an aging strengthened Cu-Ti-Cr-Mg alloy,and the microstructure and properties of the alloy were investigated in detail.The results showed that the samples deformed by the combination of cryogenic equal channel angular pressing(ECAP)and rolling had good comprehensive properties after aging at 400℃.The tensile strength of the peak-aged and over-aged samples was 1120 MPa and 940 MPa,with their corresponding electrical conductivity of 14.7%IACS and 22.1%IACS,respectively.ECAP and cryogenic rolling introduced high density dislocations,leading to the inhibition of the softening effects and refinement of the grains.After a long time aging at 400℃,the alloy exhibited ultra-high strength with obvious increasing electrical conductivity.The high strength was attributed to the synergistic effect of work hardening,grain refinement strengthening and precipitation strengthening.The precipitation of a large amount of Ti atoms from the matrix led to the high electrical conductivity of the over-aged sample.

Effects of direct aging treatment on microstructure,mechanical properties and residual stress of selective laser melted AlSi10Mg alloy

Direct aging treatment is an important post-processing procedure,yet little research has been done on how it balances the mechanical properties and the stress removal for selective laser melted(SLMed)AlSi10Mg alloys.Here,we proposed a typical direct aging treatment on SLMed AlSi10Mg alloys,and studied the effects on their microstructure,properties and residual stress evolution.The results indi-cate that the as-built microstructure is mainly composed of fine cellularα-Al and reticulated Si phases,and some pre-existing precipitates and dislocations are found in these cells.The direct aging treatment promotes the precipitation of nano-scaled Si phases and preserves a network-like Si structure.Therefore,the strength of the peak-aged alloy increases while the ductility decreases.As the aging temperature in-creases from 160 to 200℃,aging hardening behavior was accelerated significantly.Aging at 160℃ for 4-9 h removes 32.0%-43.0%of the residual stress,which is attributed to the decomposition of the su-persaturatedα-Al matrix,the precipitation of the nano-Si phase and the exposure of low-angle grain boundaries(LAGBs).Considering the overal alloy performance obtained,over-aging at 160℃ for 4 h is the optimized heat treatment regime.Under this condition,the yield strength(YS),ultimate tensile strength(UTS)and elongation(EL)of the alloy in the transverse and longitudinal direction are 309.5 MPa,464.4 MPa and 8.3%and 286.4 MPa,464.9 MPa and 5.1%,respectively.

Improvement of tensile superelasticity by aging treatment of NiTi shape memory alloys fabricated by electron beam wire-feed additive manufacturing

For the first time,this work comprehensively studied the effectiveness of precipitation hardening achieved by aging treatment in improving the tensile superelasticity of NiTi alloys fabricated by elec-tron beam wire-feed additive manufacturing(EBAM),which possesses inherent advantages in producing dense and oxidation-free structures.Aging treatments under three temperatures(450,350,and 250℃)and different durations were conducted,and the resultant performance of tensile superelasticity,together with the corresponding evolution of precipitation and phase transformation behavior were investigated for the EBAM-fabricated NiTi alloys.Results showed that by appropriate aging treatment,EBAM fabricated NiTi alloys could achieve excellent recovery rates of approximately 95%and 90%after the 1st and 10th load/unload cycle for a maximum tensile strain of 6%,which were almost the highest achieved so far by AM processed NiTi alloys and close to those of some conventional NiTi alloys.The improvement of tensile superelasticity benefited from the fine and dispersive Ni4Ti3 precipitates,which could be introduced by aging at 350℃ for 4 h or at 250℃ for 200 h.Moreover,the large amount of Ni4Ti3 precipitates would promote the intermediate R-phase transformation and bring a two-stage or three-stage transformation sequence,which depended on whether the distribution of the precipitation was homogeneous or not.This work could provide guidance for the production of NiTi alloys with good tensile superelasticity by EBAM or other additive manufacturing processes.