Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： The directionally solidificated (DS) Co-based superalloys are widely used in aircraft turbine vanes due to the good stress-rupture parameters and excellent hot corrosion resistance. The cyclic change of temperatures and complex stress state thermal fatigue (TF) cracks happen frequently in vanes during service. However, most of the work are conducted in Ni- based superalloys and there is rare report concerning the TF behavior of DS Cobased superalloys. Furthermore, due to the residual strain accumulated during processing, shot peening, grinding and recrystallization (RX) frequently occur when the DS components are exposed to high temperatures. It is believed that RX may change the microstructure, especially adding more grain boundaries to DS alloys, and result in the reduction of the mechanical properties of DS superalloys. Therefore, in this work, V-notch plate specimens with notch direction perpendicular and parallel to the DS orientation are machined from the DS plate. Local RX grains are prepared (local indented and then heat treated) in the notch areas of some samples. TF test is conducted between 1000 ℃ to room temperature. The effect of DS orientation and RX on TF properties of a DS Co-based superalloy is investigated. The results indicate that the cracks propagate along the interdendritic regions in the samples with notches parallel to the DS direction, which exhibites lower TF properties than samples with notches vertical to the DS direction. TF cracks initiate and propagate along RX boundaries in samples containing RX grains. Precipitation of M23C6 carbides is found along the RX boundaries during TF tests. Due to the oxidation at the tip of crack, M23C6 desquamates and leads to the formation of micro voids, which accelerates the crack propagation and decreases TF properties of tested alloy. In samples with notches parallel to the DS direction, cracks preferentially propagate along the RX grain boundaries.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Service safety of turbine blades in aircraft enγines are threatened by microstructural and property deγradation instantly caused by overheatinγ durinγ service. Systematic investiγations about microstructural deγradation durinγ overheatinγ exposures and its influence on mechanical properties of turbine blades durinγ service are limitedly reported. In this work, microstructure and mechanical properties of γH4033 alloy, which was sectioned from the shank of a serviced 2nd staγe turbine blade in an aircraft enγine, were studied after overheatinγ at 900~1100 ℃ for 3 min. Microstructural deγradation durinγ overheatinγ exposures as well as its influence on room temperature hardness and stress rupture life at 700 ℃, 430 MPa were analyzed. The results of microstructural characterization indicated that the coarseninγ and dissolution of γ' precipitates were introduced by overheatinγ exposures, and all of the γ' precipitates dissolved at 980 ℃ for 3 min. γradual dissolution of γrain boundary (γB) carbides was observed with the increase of overheatinγ temperature. Complete dissolution of γB carbides at 1100 ℃ resulted in γrain γrowth. The room temperature hardness after overheatinγ exposures decreased γrossly with the dissolution of γ' phase. Due to the dissolution and re-precipitation of γ' phase as well as the dissolution of γB carbides, the stress rupture life under 700 ℃, 430 MPa of γH4033 alloy was initially increased and then decreased siγnificantly.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： The effect of Hf on the as- cast, heat- treated microstructures and stress rupture properties under 1100 ℃ and 140 MPa was investigated in four second generation Ni-based single crystal superalloys DD11 with various levels of Hf (0~0.80%, mass fraction) additions. The results indicate that increasing Hf addition resulted in decreasing the solidus and liquidus temperatures, while it enhanced the volume fraction of (g +g') eutectic and MC carbide as well as solidification segregation. The number of micropores reduced significantly and the volume fraction of residual (g +g') eutectic and MC carbide increased after heat treatment as Hf content increased. Compared to the Hf-free alloy, the stress rupture life was observed to increase in the alloys with 0.40%Hf, but dropped in the alloy containing 0.80%Hf. Hf addition increased the elemental partitioning ratio of Re, Mo, Cr, resulting in increasing g /g' misfit and decreasing the spacing of g /g' interfacial dislocation networks. The solution strengthing effect was also improved with the enhanced concentration of Re, Mo and Cr in g phase in Hf-modified alloys. However, when the Hf content was 0.80% in DD11 alloy, the stress rupture properties was decreased obviously due to high volume fraction of residual (g +g') eutectic and MC carbide in heat-treated microstructures.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： To reduce the weight of car body, Al-Mg-Si-Cu alloys have been widely used to produce outer body panels of automobiles due to their favorable high strength-to-weight ratio, corrosion resistance, weldability and good formability. Al- Mg- Si- Cu alloys belong to age- hardenable aluminium alloys, whose strength derives mainly from the matrix precipitation during aging treatments. However, their bake hardening response still need to be further improved to enhance their dent resistance. A novel thermo-mechanical treatment consisting of conventional pre-aging, pre-deformation and re-aging was developed to enhance the tensile properties and bake hardening increment of Al-Mg-Si-Cu alloys. In this work, the effect of pre-deformation on the precipitation behaviors of Al-Mg-Si-Cu alloy was studied by DSC, mechanical property measurement and TEM. The results show that, the GPzone dissolution rate decreases with increasing pre-deformation during the slow heating up process for the pre-aged alloy, the corresponding activation energies of 0, 5% and 15% pre-deformed alloy calculated by Avrami-Johnson-Mehl method are 137.1, 189.5 and 141.3 kJ/mol, respectively. If the pre-deformed alloys are directly bake hardened at 185 ℃ for 20 min, precipitation and bake hardening increment can be greatly improved by pre-deformation (the highest bake hardening increment is 160 MPa), but the bake hardening increment rate gradually decreases if the pre- deformation is above 10%. In addition, the GP zone dissolution rates of pre- deformed alloys after bake hardening treatment are much lower when the heat treatment temperatures are below one certain value, but if the treatment temperatures above it, the corresponding GP zone dissolution rates are higher than that of alloy without pre-deformation, finally, the activation energy changes from high value to low value even can be observed in the ln[(dY/dT)f/f(Y)]-1/T curve. For the β″ precipitation in the alloys, with increasing pre-deformation, its activation energy gradually decreases, corresponding gradually increase of precipitation rate.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Mo5SiB2 (T2) can be used as a promising elevated-temperature structural material because of its high melting temperature (about 2200 ℃), and excellent resistance to oxidation and creep. The Mo5SiB2 (T2) alloy was prepared by both spark plasma sintering (SPS) and tube furnace sintering (TFS), and then the microstructures were characterized by XRD, SEM-EDS and TEM. The results show that the rapid heating rate is one of important dynamic conditions responsible for the synthesis of T2. Compared with traditional methods, SPS can provide the fast synthesis in a particular way of labilized plasma sintering so that the sample can be heated to the expected temperature of 1500 ℃ with a short period. The melted Si can rapidly react with Mo and B to synthesize T2 in the solid-liquid state prior to the formation of binary phases (Mo3Si, Mo5Si3, MoB, etc.) in the solid state in the range of 600~1200 ℃. The average size of grains is equal to 1.44 μm. The boundaries are clear and have the shape of a straight line without transition zones. Moreover, no defects such as dislocations were found in the T2 alloys prepared by SPS.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： New Ni-free Zr61.5Cu21.5-xFe5Al11Sn1Nbx (x=0,1, 2, atomic fraction, %) and Zr61.5Cu21.5Fe5Al12 bulk metallic glasses (BMGs) rods with diameters of 2 and 3 mm were fabricated by copper mold casting. In order to improve the plasticity of the Zr61.5Cu21.5Fe5Al12 BMG, minor Sn and Nb with lower thermal neutron cross- sections was added into the Zr-Cu-Fe-Al alloy. The experimental results showed that the glass- forming abilities of the BMGs with Sn and Nb elements were reduced slightly. Among them with Sn and Nb elements, however, Zr61.5Cu19.5Fe5Al11Sn1Nb2 BMG exhibits high compressive strength, high ductility together with extensive“work hardening”. HRTEM study verifies the glassy states of both Zr61.5Cu19.5Fe5Al11Sn1Nb2 and Zr61.5Cu21.5Fe5Al12 alloys samples. The difference between the microstructures of the BMGs samples with and without Sn and Nb elements is that the atomic arrangement in Zr61.5Cu19.5Fe5Al11Sn1Nb2 BMG is more closely than that in Zr61.5Cu21.5Fe5Al12 BMG. Positron annihilation lifetime spectroscopy study showed further that the Zr61.5Cu19.5Fe5Al11Sn1Nb2 BMG has more closely atomic arrangement than the Zr61.5Cu21.5Fe5Al12 BMG. The structural free-volume size of the former BMG is smaller than that of the latter BMG. And the total free-volume amount of the former BMG is obviously higher than that of the latter BMG. Uniformly distributed free volume is beneficial to improve the shear band formation, branching, and interactions of the Zr61.5Cu19.5Fe5Al11Sn1Nb2 BMG, which increases finally the compressive ductility of the BMG.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： High Nb-TiAl alloys, which being regarded as a new generation TiAl alloy, had attracted more and more attention for their higher operating temperature and better oxidation resistance than conventional TiAl alloys. It was found that silicide particles in high Nb-TiAl alloys were Nb5Si3 rather than Ti5Si3 precipitated in TiAl alloys. In this work, the effect of Nb5Si3 phase on the microstructure and room-temperature tensile properties of high Nb-TiAl alloy was studied. The experimental results showed that the precipitation temperature of silicide was between 1000~1200 ℃. Precipitates located in the colony boundary, b(B2) segregation and between g/a2 lamella. The tensile properties of as-cast alloy with Si addition increased. Because the formation of Nb5Si3 precipitates resulted in the reduction of Nb content, which was one of b(B2) phase stable elements. Therefore, the volume fraction of b(B2) phase obviously decreased due to Si addition. However, after heat treatments, the tensile properties of Si containing high Nb-TiAl alloy gradually reduced with the increasing of heat treatment temperature. Silicide particles which precipitated along lamella leaded to generation and propagation of cracks. Moreover, silicide particles further precipitated due to tensile stress which increased the rate of crack propagation. Si addition leaded to g phase area expanded. g single-phase region formed between 1280~1300 ℃. Silicide precipitated in colony boundary resulted in bulk g+b(B2) phases, which weaken the grain boundaries. While silicide precipitated in lamella leaded to formation of secondary g lath which split the initial lamella microstructure.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Plasma arc cold hearth melting (PAM) is an effective technology to produce high purity titanium alloy ingots which are widely used in aeronautic and astronautic industries. To date, the development of PAM in our country is still at initial stage. It is necessary to investigate the melting parameters of PAM and the following thermal mechanical processing of the ingots fabricated by PAM. In this study, the TC1 alloy ingots casted by PAM were cogged at b transus temperature and then rolled by unidirectional rolling and cross rolling in the a+b phase field. The typical widmanstatten structure of cast- ingots turned to transformed b morphology after cogging at b transus temperature in which the a phases forms in smaller colonies of laths. After the unidirectinal rolling in the a+b phase field, the a colonies were distorted and the a laths re-arranged along the rolling direction, while they had weaker directivity after cross rolling. The sheets rolled by both unidirectional and cross rolling showed typical prismatic texture. After annealing treatment below the b transus temperature, the a phases turned to equiaxial morphology. The ambient yield strength of the sheet in transverse direction was significantly higher than in rolling direction, which could be attributed to the strong prismatic texture introduced by hot rolling process.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： To reduce the weight of car body, Al-Mg-Si-Cu alloys are becoming increasingly attractive as a candidate for material substitution used to produce the outer body panels of automobiles because of their favorable bake-hardening response. However, the formability still needs to be further improved compared to steels. In this work, the effect of the thermomechanical processing on the mechanical properties and microstructure of Al-Mg-Si-Cu alloy is studied through tensile test, OM, SEM and TEM observation, as well as EBSD characterization. The results reveal that there is almost no change in both strengths and strain-hardening exponent n of the sheets in T4P condition after different thermomechanical processing, but the average plasticity strain ratio r, planar anisotropy Δr and elongations in the three directions show obvious differences. The sheet undergone hot rolling, cold rolling, intermediate annealing, cold rolling and solution (processing II) has a better formability (r= 0.6187) and a weaker planar anisotropy than that subjected to hot rolling, intermediate annealing and then cold rolling before solution treatment (processing I). Although the particle stimulated nucleation (PSN) effect of processing I is remarkable during solution treatment, due to the appropriate controlling cold deformation and distribution of second-phase particles with different sizes in processing II, most of the recrystallization grains are equiaxial and the recrystallization texture is only consisted of CubeND, Cube and H with a low intensity. At last, according to the relationship between the microstructure and the thermomechanical processing, the microstructure evolution model during different thermomechanical processes is established.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Casting microporosity defect is one of the important issues for as- cast HK40 alloys preparation, which is of great importance to application performance of the alloy castings. A comprehensive understanding of the mechanism on formation of the casting microporosity defect is still unclear for the alloys. In this work, the casting microporosity defect and influences of boron micro-alloying on the as-cast microstructures and microporosities in HK40 alloys castings were investigated by means of SEM, OM and XRD, etc.. The microstructures in the HK40 alloys with and without boron micro-alloying after quenching at high temperatures were also examined to check the solidification characteristic change attribute to boron addition. The results show that there are two types of casting microporosities in the castings. Type A is mainly caused by the rapid growth of dendrites and thus dendritic bridge connecting which lead to feeding shortages between the bridge dendrites. Type B is, however, resulted by the growth of M7C3 carbides in coarsened dendritic morphology which induce to the feeding channel blockage in adjacent interdendritic regions. Boron micro-alloying decreases the tendency of columnar grain formation and refines the dendrites in HK40 alloys which therefore suppresses the casting microporosity defect of type A. Additionally, boron micro-alloying not only increases the volume fraction of eutectic phases, but also changes the M7C3 carbides in dendritic morphology into the M23C6 carbides in lamellar morphology, which prevents the feeding channal blockage in adjacent interdendritic regions, thus reduces the casting microporosity defect of type B.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： To reduce the weight of car body, Al-Mg-Si-Cu alloys have been used to produce outer body panels of automobiles due to their relatively good formability in the solution treated condition and high strength in the age hardened condition. However, their formability is significantly poor compared to that of steels, which are the major drawbacks to wide-scale application of aluminum in the automotive industry. The microstructural characteristics developed during recrystallization, most notably grain size and crystallographic texture, play a dominant role in controlling the mechanical properties and formability of sheet in the T4 condition. In this work, the effect of particles with different sizes on the mechanical properties, microstructure and texture of Al-Mg-Si-Cu alloys was studied through tensile test, OM, SEM, TEM and EBSD measurement. The results reveal that with increase of solute concentration, the average plastic strain ratio rˉ, yield strength and ultimate tensile strength increase, but the elongation decreases and with different extents in the three directions. In addition, the number of observed particles with different sizes in the alloy matrix such as Mg2Si, Al15Mn3Si2 and a-Al(Fe, Mn)Si phases also increases. When the size and concentration of the se particles are controlled appropriately, lots of finer recrystallized grains can form during solution treatment due to the particle stimulated nucleation (PSN) effect of coarse particles and pinning effect of finer particles. The main texture components include CubeND18, Goss{011}<100>, P{011}<122> and Cu{112}<111> for the alloy with fine-grained structure. At last, according to the relationship among alloy composition, thermomechanical processing and microstructure, the model of nucleation and growth of recrystallized grains affected by the particles with different sizes was also proposed.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Ni- based single crystal superalloys have been widely used for blades and vanes in gas turbine. However, recrystallization (RX) induced by residual strain has been a serious problem for the application of single crystal superalloys. In previous work, effect of microstructure, such as g', g/g' eutectics and carbides, as well as heat treatment parameters, on the RX behavior have been studied. However, the effect of alloy elements on the RX behavior has rarely been reported. Therefore, in this work, the effect of the important solution strengthening elements, W and Re, on the deformation and RX of solution heat treated Ni-based single crystal superalloys was investigated. At first, two single crystal superalloys were prepared, and W and Re were added into one alloy among them. After solution heat treatment, these two single crystal superalloys were deformed by shot-peening or Brinell indentation. Then these deformed samples were heat treated to observe the microstructure of RX. It indicated that RX depth decreased with the addition of W and Re irrespective of deformation mode and heat treatment temperature. Short time heat treatment experiment of indented and shot-peened samples both indicated that incubation period of RX was prolonged and nucleation of RX was slowed with the addition of W and Re, which verified that RX was suppressed by W and Re. After shot-peening, micro-hardness of the alloy with W and Re increased, but the depth of deformation zone was obviously reduced. Higher density of dislocation was found in the single crystal superalloy with W and Re, and also lots of dislocation tangles were observed. So, in this alloy, dislocation annihilated slowly, that is, recovery was slowed down, which prolonged the incubation period of RX. During the process of RX grain growth, the maximum RX grain boundary migration velocity was reduced with the addition of W and Re. Moreover, the change of mean RX grain boundary migration velocity showed the same trend with the micro-hardness along the direction of RX depth.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-18 Cooperative journals: 《材料研究学报》
Abstract： The hot deformation behavior of as spray-formed Nb-containing AISI M3: 2 high speed steel has been investigated by compression tests at a temperature range of 950-1150℃ and a strain range of 0.001-10 s- 1 with 50% reduction. Processing maps were developed according to the principles of Dynamic Material Model. It was found that the flow curves assumed the classic shape of dynamic recrystallization (DRX)-rising to a peak, following a softening to a steady state. The hot working process of the steel can be carried out safely in the domain of (Td: 1050-1150℃, ε̇: 0.01-0.1 s-1). To obtain microstructures of the steel with fine grains and uniform distribution of fine granular carbides, the hot working process should be carried out at 1150℃ and strain rate of 0.1 s- 1. The flow instability took place when strain rates exceed 1 s-1. After a proper hot working and heat treatment, the hardness and bending strength of the spray-formed Nb-containing M3:2 high speed steel is 67 HRC and 3467 MPa, respectively.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-18 Cooperative journals: 《材料研究学报》
Abstract： The La0.6Pr0.4Fe11.4Si1.6B0.2 alloy was produced by using industrial grade raw materials. The phase constituents and thermal magnetic properties of the alloy were characterized by X-ray diffraction with Cu kα radiation and vibration sample magnetism respectively. The influence of hydrogen absorption pressure on magnetocaloric effect and hydrogen desorption process were investigated. Results show that the annealing treated alloy was subjected to hydrogenation at 0.13 and 0.2 MPa, correspondingly its Curie temperature increased to 320 and 321 K respectively. The taking place of dehydrogenation was much easier for the alloy hydrogenated at lower absorption pressure rather than that at higher pressure. The Curie temperature of the alloy hydrogenated at 0.13 MPa and then dehydrogenated at 473K could lower to room temperature range, correpondingly the maximal magnetic entropy of the hydrides decreased while the relative cooling power were increased.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-18 Cooperative journals: 《材料研究学报》
Abstract： Effect of heat treatment on the microstructure and mechanical properties of a high Nb-containing TiAl alloy sheet was investigated, which was fabricated by directly hot-rolling a packed alloy ingot. The obtained sheet mainly consisted of remnant coarsening lamella, recrystallized γ grains and strip-like β phase along rolling direction. Followed by variant heat treatments, the coarse lamella and β phase were eliminated, and various typical microstructures were appeared, such as duplex, near fully lamellar and fully lamellar ones. Mechanical properties of the sheet with duplex microstructure were tested at room and high temperatures respectively. The results showed that the strength and ductility of the sheet at room temperature were improved after heat treatment. The brittle-ductile transition temperature was in the range of 850-900℃, and the corresponding fracture mode transformed from transgranular fracture to the nucleation and coalescence of voids.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-18 Cooperative journals: 《材料研究学报》
Abstract： The long-term air oxidation behavior of in situ synthesized composites MoSi2-SiC with different volume fractions of SiC at 700 ℃ for 1000 h was investigated. The disintegration (pest) of the composites has not been observed after oxidation for 1000 h. The oxidation resistance of composites is significantly higher than that of monolithic MoSi2. The in situ synthesized composite MoSi2-30%SiC possesses higher oxidation resistance than the traditional composite with the same chemical composition fabricated by hot-pressing the mixture of commercial powders of MoSi2 and SiC. The oxide scale formed on the prepared composite is only composed of amorphous silica, therefore, the oxidation reaction of the materials may mainly occur between MoSi2 and O2. Silicon and molybdenum may simultaneously be oxidized at 700℃ for the composite, however, due to the faster volatilization of MoO3, thereby a thin continuous and dense amorphous SiO2 protective scale is rapidly formed on the composite surface, so the composite exhibits excellent long-term oxidation resistance.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-18 Cooperative journals: 《材料研究学报》
Abstract： The corrosion behavior of the newly developed Al-Mg alloys was investigated in terms of their alloying element and thermo-mechanical treatments by means of intergranular corrosion test, exfoliation corrosion test, scanning electron microscopy and transmission electron microscopy. The results show that, with the increase of Mg content the mass loss of the alloys in concentrated nitric acid increased, correspondingly their intergranular corrosion resistance decreases. Zn addition to the Al-Mg alloys led to the formation of Mg32(Al, Zn)49 phase at the grain boundary, which dramatically increased the intergranular corrosion resistance of the alloys. The corrosion resistance of the alloys was also modified by thermo- mechanical treatment. Both intergranular corrosion resistance and exfoliation corrosion resistance of the alloys were dramatically increased by a proper post stabilizing treatment after cold rolling reduction. The residual stress, higher dislocation density and morphology of elongated grains after cold rolling reduction can lead to more continuous precipitation at the grain boundary, thus decrease the corrosion resistance of the alloys.
Subjects: Materials Science >> Materials Science (General) submitted time 2016-11-15 Cooperative journals: 《金属学报》
Abstract：第二相强化是一种传统且十分有效的金属材料强化方式，但在导致高强度的同时常伴随韧塑性的大幅度下降。本文归纳总结了本课题组近几年来在几种典型的先进金属材料（高性能钢铁材料、高熵合金及块体非晶合金）中应用第二相强化机制的研究工作。研究发现，通过调控第二相与基体组织的界面特性和性能匹配，可以有效调控第二相的尺寸、体积比及形貌等特征，从而大幅度提高这些材料的综合力学性能。
Subjects: Materials Science >> Materials Science (General) submitted time 2016-11-04 Cooperative journals: 《金属学报》
Abstract：利用SEM原位观察技术研究了近片层Ti-45Al-8Nb-0.2W-0.2B-0.1Y合金在750℃疲劳蠕变交互作用下的裂纹萌生及扩展行为，循环实验采用在最大拉应力保载的梯形波。结果表明，裂纹主要在片层团界面萌生，裂纹萌生方式包括蠕变空洞和疲劳微裂纹。片层团界面处的微裂纹先通过吞并蠕变空洞或在裂纹尖端应力集中作用下沿片层团界面进行扩展，然后相互连接长大；当裂纹扩展受到不同取向的片层团界面阻碍时，受阻的裂纹开始沿试样厚度方向扩展，且附近伴随出现垂直于载荷方向的微裂纹；最终受阻的裂纹相互连接直至合金断裂。将实验结果与该合金在相同条件下疲劳变形和蠕变变形的原位观察结果进行了比较。结合实验结果建立了高Nb钛铝合金在疲劳蠕变交互作用下裂纹萌生及扩展示意模型。
Subjects: Materials Science >> Materials Science (General) submitted time 2016-11-04 Cooperative journals: 《金属学报》
Abstract：采用DSC、力学性能测试及TEM研究了预变形对Al-Mg-Si-Cu合金析出行为的影响。结果表明，预时效态合金在慢速率升温过程中，GP区溶解速率均随预变形量的增加而降低，利用Avrami-Johnson-Mehl方法求得经0%、5%和15%预变形后合金的GP区溶解激活能分别为137.1KJ/mol、189.5KJ/mol和141.3KJ/mol；若合金经不同预变形后直接进行185℃/20min烤漆硬化，预变形可有效促进沉淀相析出，提高烤漆硬化增量，最高达160MPa，不过预变形量大于10%时合金烤漆硬化增幅减缓；此外，经预变形处理后烤漆态合金的GP区溶解速率在一定温度下均较低，但高于某一温度后，相应的GP区溶解速率均高于未经预变形处理的，最终获得的ln[(dY/dT)φ/f(Y)]-1/T曲线甚至会出现高激活能向低激活能转化现象；不过随预变形量增加，β〃相析出激活能不断降低，析出速率不断增加，相应的TEM组织观察结果与此非常吻合。
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