均匀化退火等温冷却对Mg-10Al-1Zn镁合金组织性能的影响

对Mg-10Al-1Zn镁合金进行均匀化退火等温冷却处理,探讨等温温度和时间对β-Mg17Al12相析出形貌和合金力学性能的影响。研究结果表明:在420℃保温24h再经200~300℃保温1~6h后,β-Mg17Al12相均以层片状形态均匀析出。β-Mg17Al12相析出量随时间延长而增加,平均层片间距随等温温度升高而增大。合金在420℃保温24h再经250℃保温2h后,布氏硬度达到最高值80.1HB。     

热处理对Al-Cu合金电导率的影响

通过电导率测量、硬度分析和金相组织观察,研究了不同热处理工艺对Al-4.0%Cu(质量分数,下同)合金电导率的影响,分析了析出相、合金硬度和电导率之间的关系。实验结果表明,Al-4.0%Cu合金的电导率主要受基体中Cu固溶度和析出相状态的影响;双级时效处理对电导率和硬度的决定因素主要为二级时效的温度与时间,一级时效后合金的电导率和硬度会随着二级时效发生改变;退火后的Al-4.0%Cu合金于350℃保温24h后,可获得较高的电导率,此时基体中的析出相为细小、弥散的θ相。     

强塑性变形下Al-Cu合金不同析出相的回溶及性能变化

采用双向反复压缩变形研究了Al-Cu合金中不同析出相的回溶速度及性能变化.结果表明:在强塑性变形过程中,GP区回溶的速度最快,介稳相(θ" θ'及θ')次之,稳定相(θ)最慢.强塑性变形引起的脱溶作用较小,而导致第二相回溶的作用较大.GP区状态下合金在压缩后硬度升高最大,过饱和固溶体、介稳相(θ" θ')和稳定相(θ)状态下依次减小.     

均匀化处理对新型Al-Zn-Mg-Cu铝合金组织及锻造性能的影响

采用扫描电镜观察(SEM)、透射电镜(TEM)、高温拉伸性能和高温冲击性能测试等方法,研究了不同均匀化处理工艺对一种采用常规半连续铸造方法生产的新型Al-Zn-Mg-Cu合金组织和锻造性能的影响。结果表明:随均匀化温度的升高,合金铸锭中的枝晶组织及难溶非平衡共晶相逐渐溶入基体中;当均匀化温度低于450℃时,基体中仍残留部分枝晶组织,并且合金的工艺塑性偏低;当均匀化温度达到470℃时,枝晶组织充分回溶到基体中,使铸锭获得最优的工艺塑性。铸锭经470℃/36h均匀化处理后,通过工艺塑性实验确定合金在380~430℃之间具有良好的锻造性能。根据以上实验结果,确定该新型Al-Zn-Mg-Cu合金的均匀化处理工艺为470℃/36h;锻造温度为380~430℃。     

6101铝合金时效过程中析出相对电阻率的影响

采用硬度测试、原位电阻测试及TEM等手段,研究了6101铝合金在175~195℃下时效析出相对相对电阻率(Δρ%)的影响,利用修正的马蒂森定则计算了175℃时不同时效时间析出相对相对电阻率的影响,得到了影响合金力学性能和导电率的温度时间判断依据。结果表明,随着温度的升高,时效初期团簇形成的时间越短,相对电阻率越低,硬度峰值也越低;175℃时效后期,析出相的密度增加,相间距减小,析出相对相对电阻率的影响基本稳定,导电率基本稳定。借助研究结果,确定了以力学性能优先和导电率优先的时效制度175℃/680min和195℃/220min,性能测试显示选取依据合理。     

Al-Cu-Mg-Ag耐热铝合金断续时效处理研究

采用维氏硬度测试、拉伸性能测试和透射电子显微分析技术,研究了断续时效处理对Al-Cu-Mg-Ag耐热铝合金组织与性能的影响。结果表明,较低的二次时效温度能够促进θ′相的析出,抑制Ω相的析出,降低合金强度,提高合金的伸长率;而较高的二次时效温度则会促进Ω相的析出,抑制θ′相的析出,细化Ω相的尺寸,并且能够改善强化相在晶界的分布,从而提高合金的强度和伸长率。合金适宜的断续时效制度为185℃/2h+150℃/6h。     

Al-Cu合金析出相在等径角挤压中的演变

为了研究Al-Cu合金中两种不同析出相(θ′和θ相)在ECAP变形过程中的变化.采用透射电镜(TEM)和硬度测试方法研究了析出相形貌变化以及对合金性能的影响.结果表明:在本实验中,θ′和θ相其破碎、回溶速度明显不同,两者的破碎方式也不同.θ′相先是与基体失去取向关系,随后从其内部产生位错使其破碎,而θ相是被外部基体位错所切割、破碎.θ′相与位错的相互作用方式类似于绕过机制,θ相与位错的作用方式类似于切割机制.两种状态样品的硬度在变形过程中的变化趋势相同,但在第1道次后θ相状态样品的硬度增加值高于θ′相状态.     

Cu-Cr-Zr-Mg合金时效组织与性能

为了研究时效工艺对Cu-0.3Cr-0.15Zr-0.05Mg合金显微组织及性能的影响,在时效温度400～650℃和时效时间1～11h条件下,得到时效工艺参数与硬度和电导率的曲面关系,并利用透射电镜分析合金时效后的微观形态和析出相.研究结果表明:合金固溶后470℃时效4 h,硬度和电导率可达HV108和45 S·m-1,析出相为Cr、Cu4Zr和有序的CrCu2(Zr,Mg)相;550℃时效1 h后硬度和电导率仍具有HV106和46.8 S·m-1,析出相完全转变为Cr和Cu4Zr.     

热处理工艺对Mg-3Zn-0.6Zr合金组织和性能的影响

本工作采用的热处理工艺分为均匀化处理及固溶处理,通过金相显微镜、扫描电镜、能谱分析、X射线衍射分析、压缩试验和硬度测量等多种实验方法,研究Mg-3Zn-0.6Zr合金铸态和热处理态的组织及性能。研究发现,均匀化处理后,铸态合金晶粒细化,抗压强度提高到338.3 MPa;固溶处理后,铸态合金中的MgZn第二相逐渐溶解到α-Mg基体中,抗压强度提高到431.1 MPa。最后,确定了最佳热处理工艺为:固溶处理温度400℃,保温8h,水冷。     

固溶时效对1Cr21Ni5Ti双相不锈钢组织的影响

本工作以1Cr21Ni5Ti双相不锈钢为原材料,对1 000~1 350℃固溶30 min+650~1 000℃时效1~1 440 min后的显微组织及σ析出相进行观测,描述了不同处理条件下的组织特征,绘制出σ相析出TTP曲线图。结果表明:随着固溶温度的升高,铁素体含量增加,奥氏体含量减小,双相不锈钢组织发生再结晶和晶粒长大。铁素体与奥氏体中Cr、Ni元素发生均匀化,各相中的含量差异降低。σ相优先在铁素体与奥氏体相界处形核,随着时效温度的升高和时效时间的延长,σ相长大、粗化并向铁素体基体延伸;时效时间越长,析出相越多;当温度达到750℃,σ相析出速度最快,之后随着温度的升高而降低。σ相析出温度范围为650~850℃,析出鼻尖温度为750℃。     

微量Ag元素对Cu-15Cr原位复合材料组织和性能的影响

以Cu-15Cr、Cu-15Cr-0.1Ag合金为研究对象,结合金相显微分析、扫描电镜分析、电导率测试、硬度测试等实验手段,研究了微量Ag元素对不同状态下Cu-15Cr合金组织和性能的影响。结果表明:微量Ag元素的加入能够显著减少第二相偏聚析出,对第二相有一定的细化作用,在相同的形变热处理工艺下,保持电导率不显著降低的同时明显提高了合金的硬度和延伸率,使得合金的综合性能显著提升。     

预变形对Al-Cu-Li-Mn-Zr合金的第二相析出及力学性能的影响

采用维氏硬度、常温拉伸及透射电子显微镜等测试手段,研究了不同预变形状态对Al-Cu-Li-Mn-Zr合金中第二相析出行为及力学性能的影响。结果表明,未经预变形的峰值时效态Al-Cu-Li-Mn-Zr合金的析出相有T_1(Al_2CuLi)相、θ′(Al_2Cu)相,且存在极少量的χ(Al_5Cu_6Li_2)相。预变形的引入使T_1相的析出量显著增加,同时抑制了θ′相的形成,但对χ相的析出量的影响却较小。由此可知,经预变形的合金在峰值时效态的析出相以细小弥散的T_1相为主。经定量统计可知,预变形量越大,作为主要析出相的盘片状T_1相的直径越小,但厚度及体积分数几乎保持不变。此外,随着预变形量的增大,峰值时效态合金的屈服强度和抗拉强度升高,塑性降低。     

Unravelling the precipitation evolutions of AZ80 magnesium alloy during non-isothermal and isothermal processes

The precipitation evolutions of Mg-Al-Zn alloys play essential roles in their mechanical properties,corro-sion performance,formability,plastic deformation mechanisms and texture development.In the present work,the precipitation evolutions of AZ80 magnesium alloy during both non-isothermal and isothermal processes were unraveled by utilizing in situ electrical resistivity monitoring,hardness testing,differen-tial scanning calorimetry and microstructural characterization.The results showed that discontinuous precipitation(DP)and continuous precipitation(CP)occurred competitively during non-isothermal and isothermal processes.The precipitation of dominant 3-Mgi7Ali2 phase during non-isothermal processes was highly dependent on the thermal history.During isothermal processes,the precipitation behavior of AZ80 magnesium alloy could be considered as the functions of holding temperature and time.At lower temperatures,massive DP and CP were gradually formed to equally strengthen the alloy.At higher tem-peratures,the Ostwald coarsening was characterized in the later stages and indicated to slightly soften the alloy.Isothermal time-temperature-precipitation curves and quantitative precipitate evolution were estimated to unravel precipitation characteristics and their strengthening functions.     

Ageing reactions in a high carat gold alloy for dental porcelain bonding

The phase transformation during continuous heating of a high carat gold alloy used for porcelain bonding was investigated by electrical resistivity measurements, hardness tests, X-ray diffraction and scanning and transmission electron microscopy. Four reaction stages (I, II, III and IV) were found. Stage I corresponded to the formation of a short-range order. A discontinuous precipitation took place in stage II, which contributed to remarkable hardening. Stages III and IV were reactions to the stable phases at each temperature region, and resulted in softening. The activation energies for stages I, II and III are 27.1, 33.8 and 58.2 kcal/mol, respectively.     

Precipitation behavior of Ag–Pd–In dental alloys

Age-hardening characteristics and precipitation behavior of Ag–25%Pd–3%In–1%Zn–0.5%Ir alloy were investigated in detail by means of hardness testing, X-ray diffraction, electron microscopy and resistivity measurement. The solution treating could be accomplished at 980 °C and the aging in the temperature range from 950 to 850 °C occurred by continuous precipitation. The aging in the temperature range from 850 to 450 °C occurred first, forming GP-zones with a hardness increase and then in overaging stage by forming discontinuous precipitation, which consisted of lamellae of solute (Pd, In, Zn) depleted Ag-rich phase and (Pd,Ag)₃(In,Zn) intermetallic phase. The hardness increased very fast to its peak in 10 min during aging at temperatures between 450 and 550 °C.     

Effect of Microstructure on Thermal Expansion Coefficient of 7A09 Aluminum Alloy

The relationship between microstructure evolution and coeffcient of thermal expansion (CTE) of 7A09 alu- minum alloy was investigated in this paper. Differential scanning calorimetry (DSC) was combined with transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) to investigate microstructure evolution taking place in 7A09 aluminum alloy during heating and cooling process. The corresponding CTE curves of the 7A09 alloy were recorded by thermal dilatometer. Results indicated that GPII zones and η phase were main precipitates in the highest strength tempered (T6) 7A09 alloy. The η phase was the main participate in 7A09 alloy during the cooling process. The nonlinear dependency existed between CTE and temperature in both changing temperature processes. During the heating process, obvious additional contraction of alloy volume was directly caused by phase transition, such as dissolution of η phase, transition from η to η phase and dissolution of η phase. The additional contraction could slow down the increase of CTE greatly and be expressed in the nonlinearity of CTE curve. Volume and energy changes of alloy system inffuenced the variation trend of CTE directly, which was caused by the precipitation of η phase during the cooling process. These effects were revealed by the corresponding nonlinear change of CTE.     

Mechanical properties enhancement in Ti–29Nb–13Ta–4.6Zr alloy via heat treatment with no detrimental effect on its biocompatibility

The present investigation deals with the microstructural evolution and mechanical properties optimization of a new titanium based TNTZ (Ti–29Nb–13Ta–4.6Zr) alloy through applying a proper heat treatment strategy. The TNTZ alloy was subjected to solution treatment and cooling procedure via different medias including liquid nitrogen, water, oil, static air and vacuum furnace. The slow cooling in vacuum furnace and static air resulted in precipitation of ω phase. The formation of this phase secures an increase in the strength and hardness value, however stands detrimental to the ductility. The α″ martensite is formed due to accelerated cooling in liquid nitrogen, water and oil. This phase remains neutral to the ductility of the alloy, while its excessive formation increases the hardness and shear strength. This study proposes the liquid nitrogen quenching as a process that optimizes the mechanical properties by rendering the highest strength while preserving the ductility.     

Effect of thermomechanical treatment on spray formed Cu – Ni – Si alloy

Abstract

The heat treatment response of a spray formed Cu – 2.4Ni – 0.6Si (wt-%) alloy has been investigated. The spray formed alloy was given various thermomechanical treatments prior to isothermal aging. These treatments included solutionising and/or cold rolling with different reductions in original thickness. The variation in hardness and electrical conductivity of the alloys was measured as a function of the aging time. The results indicated the highest peak hardness value of ~250 kg mm^-2 for the alloy aged after solution treatment and cold rolling to 40% reduction in thickness, compared with the maximum hardness of 220 kg mm^-2 for specimens aged directly in the as spray formed condition. However, the electrical conductivity after aging was observed to be a maximum of 65%IACS (International Annealed Copper Standard) in specimens cold rolled to 80% reduction in thickness before aging. The aging response was observed to accelerate with the degree of cold working. Optical, scanning electron and transmission electron microscopy were used for microstructural characterisation of the materials. Precipitation of the second phase was observed to dominate in deformation bands. The alloy showed evidence of discontinuous precipitation, particularly when the alloys were cold rolled before aging. The onset of discontinuous precipitation led to a drastic deterioration in hardness of the alloys. The precipitation behaviour of the alloy is discussed in the light of microstructural characteristics associated with various processing conditions of the alloy.     

Growth kinetics of (θ′– and θ-phases in Al–3Cu alloy

Abstract

The precipitation of θ′ and θ in Al–3Cu alloy has been investigated, using a resistivity and a transmission electron microscopy (TEM) method. Both stages of the transformation obey the Avrami equation, ξ = 1? exp (?ktⁿ), where ξ is the precipitated fraction of excess solute. The growth parameters are n = 1·68±0·10 for θ′ precipitation and n = 0·63 ± 0·04 for θ precipitation, and the corresponding activation energies are 85·3 ± 10·9 and 111·1±5·2 kJ, respectively. The n-value for the θ′ precipitation stage corresponds to the model proposed by Ham for diffusion-limited growth of disc-like particles, and is in agreement with the TEM results of this investigation. The activation energy for θ′ precipitation is in the range for θ′ boundary migration reported by Aaronson and Laird. The n-value and activation energy for θ precipitation suggests a growth model in which concurrent dissolution of θ′ supplies solute to θ particles via dislocation paths.

MST/480