喷射成形高锌Al-Zn-Mg-Cu合金的时效行为

系统研究了喷射成形高锌Al-Zn-Mg-Cu合金在不同时效处理条件下的显微组织与力学性能.结果表明自然时效合金在晶界处已析出强化相;单级时效合金随时效时间的延长,晶内和晶界析出相逐渐粗化;双级时效合金的析出相进一步粗化,并且晶界析出相为断续特征;回归再时效合金具有较细的晶内组织及类似于双级时效的晶界组织.同时发现,双级时效合金的抗拉强度比峰时效合金的强度下降了13%左右,而回归再时效合金的强度优于峰时效合金的强度.     

时效制度对工业规格喷射成形7055铝合金组织和性能的影响

采用全自动控制往复喷射成形工艺制备大规格7055铝合金锭坯。锭坯经热挤压和双级固溶处理后,在不同时效工艺条件下进行双时效处理,测定时效态合金的抗拉强度(σb)、屈服强度(σ0.2)、伸长率(δ)、硬度(HRB)和电导率(γ),并观察其微观组织,研究时效制度对合金组织和性能的影响,并与120℃/24 h单级时效的合金样品进行性能对比。结果表明,锭坯经120℃/24 h时效处理后获得最高强度,抗拉强度(σb)高达725 MPa,屈服强度(σ0.2)为685 MPa,伸长率(δ)10.0%,硬度为96 HRB,电导率为30%IACS;双级时效后获得较好的塑性和抗应力腐蚀能力,但强度较低,且随着二级时效温度升高和时效时间延长,合金强度下降,伸长率增加,电导率提高。通过对正交实验结果进行分析,确定最佳双级时效处理工艺为:120℃/8 h+170℃/8 h,其综合性能最佳,σb、σ0.2和δ分别达到659 MPa、630 MPa和11.7%,硬度和电导率分别为95 HRB和39%IACS。与单级时效处理相比,电导率提高30%,抗应力腐蚀性能显著改善。     

双级时效制度对7150铝合金微观组织和性能的影响

采用拉伸测试、电导率测试和透射电镜等手段研究了双级时效制度对7150铝合金的力学性能、电导率和微观组织的影响。结果表明:在本研究范围内,第一级时效制度对合金的力学性能和电导率影响不大;合金经过120℃/8h+160℃/6h,可以达到与单级峰时效处理相当的抗拉强度,并且电导率有明显提高;第二级时效温度为168℃时效时,相比在160℃进行第二级时效,合金在具有同等电导率水平时,损失的强度相对较多,但时效时间明显变短;120℃/8h+160℃/32h双级时效后,合金的抗拉强度为560MPa,屈服强度为520MPa,延伸率为11.5%,电导率22.7MS.m-1,晶内沉淀析出相以η′和η为主,晶界析出相完全断开。     

热暴露对Al-Cu-Mg-Ag合金组织和性能的影响

研究了Al-Cu-Mg-Ag合金经时效处理165℃×2h(欠时效态)后,在不同温度(150~300℃)和不同时间(0~1000h)热暴露后的显微组织和性能.结果表明:在150℃热暴露下,随时间延长,其剩余强度先上升后下降,强度峰值出现在100h。在1000h后合金力学性能相对欠时效态无明显下降;在200~300℃热暴露时,合金的强度随时间的延长而下降,延伸率随着时间的延长而增大;在300℃热暴露时,合金的强度明显下降,暴露10h后其抗拉强度为272.5MPa,100h后其抗拉强度降至114.5MPa.欠时效状态的合金组织主要为均匀细小分布Ω相;随着暴露温度的升高,Ω相长大并粗化,晶界无析出带(PFZ)变宽.     

Sc对7056铝合金组织和性能的影响

对铸态合金进行了均匀化处理、挤压、固溶处理和时效处理,通过分析合金的化学成分,观察合金在不同状态的显微组织及析出相透射电镜(TEM)形貌,测试合金在热处理后的硬度和拉伸性能,研究了向7056铝合金中加入质量分数0.2%的Sc对合金组织和性能的影响.实验结果表明,Sc元素的加入可以明显细化组织晶粒,铸态晶粒由100~500 μm下降到50 μm左右;Sc元素的加入对合金的塑性有大幅度提高,时效处理后,合金的断后伸长率从10.82%增加到了13.60%;但屈服强度却由668 MPa下降到657 MPa.通过综合计算晶粒大小、析出相强化等因素,详细分析了Sc元素加入引起7056铝合金峰时效态屈服强度下降的原因.理论计算显示,向合金中加入质量分数0.2%的Sc元素时,峰时效处理后,合金的强度值会下降12.005 MPa,与试验值11 MPa接近.研究得到7056铝合金最佳的单级时效制度为120℃+16 h,峰值硬度和强度为195.2 HV和714 MPa,此时合金中主要强化相为圆盘状和短棒状的MgZn₂相,大小约为4~6 nm,同时存在球状的Al₃Zr相,大小约为20 nm.      

双级时效对Mg-2.8Nd-0.4Zn-0.5Zr合金微观组织和力学性能的影响

采用OM、SEM、TEM以及硬度测试和拉伸力学性能测试等手段,研究了双级时效对Mg-2.8Nd-0.4Zn-0.5Zr合金显微组织和力学性能的影响。结果表明,合金经260℃/30 min+200℃/4 h双级时效处理后,其抗拉强度和屈服强度较200℃/14 h单级时效合金分别提高23 MPa和20 MPa,并且达到硬度峰值所需时间缩短9.5 h。主要是由于第一级高温预时效过程中析出β1相,在第二级时效过程中,β1相保留,同时又析出β″相,并且β″相尺寸较单级时效后的合金更细小。在两种析出相同时作用的情况下,其强化效果明显优于单一β″相强化的单级时效处理。     

时效对新型Al-Zn-Mg-Cu合金力学及应力腐蚀性能的影响

通过力学性能和电导率测试、慢应变速率试验(SSRT)以及显微组织TEM分析,研究了不同时效制度对新型Al-7.5Zn-1.7Mg-1.4Cu-0.12Zr合金力学及应力腐蚀性能的影响。结果表明,合金的力学性能和应力腐蚀性能与时效制度密切相关。T6状态下,晶内析出相弥散细小,晶界析出相呈连续分布,合金的强度最高,抗应力腐蚀性能最差;经T7双级过时效处理后,晶界析出相粗化呈离散分布,出现明显宽化的晶间无析出带,合金的抗应力腐蚀性能得到明显提高,但其强度损失较多。经三级时效处理后,合金的组织综合了T6态和T7态的优点,使合金既有高的强度又有良好的抗应力腐蚀性能,合金的极限抗拉强度、屈服强度、伸长率和电导率分别达到580,570 MPa,16.7%和23.3 MS.m-1。     

Sc对7056铝合金组织和性能的影响

对铸态合金进行了均匀化处理、挤压、固溶处理和时效处理,通过分析合金的化学成分,观察合金在不同状态的显微组织及析出相透射电镜(TEM)形貌,测试合金在热处理后的硬度和拉伸性能,研究了向7056铝合金中加入质量分数0. 2%的Sc对合金组织和性能的影响.实验结果表明,Sc元素的加入可以明显细化组织晶粒,铸态晶粒由100～500μm下降到50μm左右; Sc元素的加入对合金的塑性有大幅度提高,时效处理后,合金的断后伸长率从10. 82%增加到了13. 60%;但屈服强度却由668 MPa下降到657 MPa.通过综合计算晶粒大小、析出相强化等因素,详细分析了Sc元素加入引起7056铝合金峰时效态屈服强度下降的原因.理论计算显示,向合金中加入质量分数0. 2%的Sc元素时,峰时效处理后,合金的强度值会下降12. 005MPa,与试验值11 MPa接近.研究得到7056铝合金最佳的单级时效制度为120℃+16 h,峰值硬度和强度为195. 2 HV和714MPa,此时合金中主要强化相为圆盘状和短棒状的MgZn2相,大小约为4～6 nm,同时存在球状的Al3Zr相,大小约为20 nm.     

时效热处理对7B50超强铝合金组织与性能的影响

通过拉伸试验、维氏硬度测试、电导率测试、晶间腐蚀与剥落腐蚀试验、金相观察及透射电镜分析等,研究新型的4级时效工艺(four-step aging,FSA),即高温短时效—低温长时效—高温短时效—低温时效工艺对Al-Zn-Mg-Cu系7B50超强铝合金组织和性能的影响。结果表明:FSA处理促使7B50铝合金晶界析出相发生球化和细化,晶界析出相的体积分数显著增大并呈非连续分布;与传统的回归再时效RRA工艺相比,经过优化的新型4级时效热处理能明显提高7B50铝合金的力学性能和抗腐蚀性能;经过150℃/5 h→110℃/24 h→150℃/5 h→110℃/12 h的4级时效处理后,合金的室温抗拉强度从582 MPa提高到685 MPa,抗腐蚀性能明显超过回归再时效(RRA)处理的合金。     

2014合金的回归再时效

本文采用拉伸实验和透射电镜法,研究了2014铝合金的回归再时效(RRA)处理.结果表明:采用欠时效(100℃(2×2h)与适当回归处理(200×5min)配合的RRA处理,可同时提高2014合金的强度和塑性.适当的回归处理能使欠时效2014合金组织中部分GP区优先长大.随后再进行峰时效处理,不仅能改善晶界析出相的尺寸和分布,而且还能使基体析出相尺寸产生明显的差异.这种尺寸有明显差异的基体析出相协同强化有利于提高2014合金的强韧性.     

轧制变形对 F-M 双相钢 0.05C-2.8Mn-4.2Ni-2Al- 1.2Mo-1.9Cu晶粒细化的影响

借助EBSD场发射扫描电子显微镜,研究了轧制变形及热处理后的铁素体/马氏体双相钢0.05C-2.8Mn4.2Ni-2Al-1.2Mo-1.9Cu显微组织演变及力学性能。结果表明,经900℃30%+780℃75%变形,500℃退火的F-M钢晶粒尺寸0.97μm,屈服、抗拉强度和延伸率分别为876 MPa,976 MPa和15.2%,经900℃30%+780℃50%变形,500℃退火的F-M钢晶粒尺寸1.54μm,屈服、抗拉强度和延伸率分别为801 MPa,895 MPa和19.4%。由轧制变形导致的晶粒细化、小角度晶界增多,是提高实验钢强度的主要原因。然而,较大的轧制变形量也使过多的小角度晶界阻碍位错运动,从而导致实验钢在塑性变形过程中,延展性略差。     

预应变与预时效对6101导电铝合金组织与性能的影响

在人工时效基础上引入预应变与预时效以提高6101铝合金的力学与导电性能。通过性能检测与组织观察,研究了合金在人工时效热处理（固溶+时效）及引入预应变与预时效后的热处理（固溶+预应变+时效,固溶+预时效+预应变+再时效）过程中显微组织、力学性能及导电性能的变化规律。结果表明:当合金经过60%冷轧变形再在180℃时效6 h后,其抗拉强度与电导率分别达到262 MPa及55.7% IACS,高于一般人工时效后的合金。当合金在180℃预时效2 h后经过60%冷轧变形,再在180℃时效6 h后,其抗拉强度与电导率进一步提升至289 MPa与58.0% IACS。引入预应变与预时效后所产生的应变强化与析出强化的交互作用,是合金的力学性能和导电性能得到提升的根本原因。      

Mechanical Properties and Fracture Behavior of Cu-Co-Be Alloy after Plastic Deformation and Heat Treatment

Mechanical properties and fracture behavior of Cu-0.84Co-0.23 Be alloy after plastic deformation and heat treatment were comparatively investigated.Severe plastic deformation by hot extrusion and cold drawing was adopted to induce large plastic strain of Cu-0.84Co-0.23 Be alloy.The tensile strength and elongation are up to 476.6 MPa and 18%,respectively.The fractured surface consists of deep dimples and micro-voids.Due to the formation of supersaturated solid solution on the Cu matrix by solution treatment at 950℃for 1h,the tensile strength decreased to271.9 MPa,while the elongation increased to 42%.The fracture morphology is parabolic dimple.Furthermore,the tensile strength increased significantly to 580.2 MPa after aging at 480℃ for 4h.During the aging process,a large number of precipitates formed and distributed on the Cu matrix.The fracture feature of aged specimens with low elongation(4.6%) exhibits an obvious brittle intergranular fracture.It is confirmed that the mechanical properties and fracture behavior are dominated by the microstructure characteristics of Cu-0.84Co-0.23 Be alloy after plastic deformation and heat treatment.In addition,the fracture behavior at 450 ℃ of aged Cu-0.84Co-0.23 Be alloy was also studied.The tensile strength and elongation are 383.6 MPa and 11.2%,respectively.The fractured morphologies are mainly candy-shaped with partial parabolic dimples and equiaxed dimples.The fracture mode is multi-mixed mechanism that brittle intergranular fracture plays a dominant role and ductile fracture is secondary.     

双级时效对7075合金应力腐蚀性能影响

双级时效处理虽能有效提高7075铝合金抗应力腐蚀开裂(SCC)性能,但同时会导致合金力学性能降低。为了同时提高7075铝合金的拉伸性能和抗SCC性能,并优化双级时效参数,对双级时效处理7075合金进行了正交试验。通过扫描电镜和透射电镜在慢应变速率实验中研究7075合金的SCC行为。结果发现,在130 ℃条件下保温4 h后,在170 ℃条件下保温8 h,合金抗拉强度、伸长率和应力腐蚀指数I_SSRT分别为488 MPa、10.8%和0.095。      

Al-6.1Zn-2.6Mg-1.6Cu 铝合金的回归再时效热处理

The effects of the retrogression temperature and time of retrogression and re-aging heat treatment(RRA) on the hardness and electrical conductivity of Al-6.1Zn-2.6Mg-1.6Cu aluminum alloy were studied. Samples were pre-aged at 120℃ for 24h as the first-stage treatment. Then, retrogression was performed at a temperature range of 170～250℃ for times of between 1min and 180min, followed by re-aging at 120℃ for 24h. Hardness (H) and electrical conductivity (EC) measurements were used to characterize the samples after RRA treatment. Analysis of the results shows: (1)The re-aging treatment at 120℃ for 24 h increases both H and EC of the retrogressed alloy in the RRA process;(2) RRA with retrogression at higher than 200℃ result in EC higher than that of peak-aged, but H lower; The change of H and EC with respect to retrogression temperature (T) and time (t) can be seen as functions of H (t) = H0 A1e(-t/s) ,EC(t) =A(1-e(-k·(t-Xc)));(3) RRA treatments with retrogression at 190℃ for 4～30min result in H and EC which are both higher than those of the peak-aged temper, and retrogression at 190℃for 30min is the industrial application that yields H of 190 HV and EC of 33.5%IACS.     

Structure and Mechanical and Corrosion Properties of a Magnesium Mg–Y–Nd–Zr Alloy after High Pressure Torsion

The structure and the properties of an Mg–Y–Nd–Zr alloy (WE43) are studied after high pressure torsion (HPT) in the temperature range 20–300°C. Structure refinement proceeds mainly by deformation twinning with the formation of a partial nanocrystalline structure with a grain size of 30–100 nm inside deformation twins. The WE43 alloy is shown to be aged during heating after HPT due to the decomposition of a magnesium solid solution. HPT at room temperature and subsequent aging causes maximum hardening. It is shown that HPT significantly accelerates the decomposition of a magnesium solid solution. HPT at all temperatures considerably increases the tensile strength and the yield strength upon tensile tests and significantly decreases plasticity. Subsequent aging additionally hardens the WE43 alloy. A potentiodynamic study shows that the corrosion resistance of this alloy after HPT increases. However, subsequent aging degrades the corrosion properties of the alloy.     

The effect of plastic deformation on Al2CuLi (T 1) precipitation

The enhancement ofT ₁ precipitation in Al-Li-Cu alloys by plastic deformation prior to aging (that is, cold work) and the subsequent increase in alloy strength is investigated. The increased understanding of the role of matrix dislocations in the nucleation and growth ofT ₁ plates, discussed in the previous paper,^[1] permits a detailed study of the phenomenon. In this paper, the effect of different levels of plastic strain on theT ₁ particle distributions as a function of aging time at 190 °C is quantified, and the subsequent influence on tensile properties is thereby described. The effect of plastic deformation is shown to decrease theT ₁ plate length and thickness, increase the number density by almost two orders of magnitude, increase the yield strength by 100 MPa, while simultaneously reaching peak strength in 20 pct of the time required without plastic deformation. Formerly Graduate Student, Department of Materials Science, University of Virginia,