LD7铝合金淬火敏感性及相变动力学规律

通过分级淬火的方法,结合所测LD7铝合金淬火态电导率和时效态硬度拟合出合金的时间-温度-转化率(TTT)曲线和时间-温度-性能(TTP)曲线。利用透射电镜(TEM)和Johnson-Mehl-Avrami(JMA)方程研究了铝合金等温淬火过程中的组织变化和相变动力学规律。结果表明:LD7铝合金TTT和TTP曲线的鼻尖温度均为350℃,孕育期约为2s,淬火敏感区间为290~410℃;等温保温过程中过饱和固溶体析出第二相粒子,鼻尖温度附近析出速率最快;随保温时间的延长,第二相富集长大且粗化,无沉淀析出区域变宽,晶界第二相连续化,导致合金强化效果下降;根据相变动力学方程拟合出的S曲线,解释了合金在350℃附近淬火敏感性最大以及淬火敏感区间合金第二相主要以针状形态析出的规律。     

6082铝合金的TTT曲线及其研究

为研究6082铝合金的淬火敏感性,采用分级淬火的方法测定了6082铝合金的时间-温度-转化率（TTT）曲线,利用XRD、TEM并结合Avrami方程研究了6082合金在等温过程中的组织变化.结果表明：6082铝合金TTT曲线的鼻尖温度约为350℃,淬火敏感温度区间为300～420℃;6082铝合金过饱和固溶体在350℃...     

7085铝合金的淬火敏感性

采用分级淬火法测定了7085铝合金的TTT和TTP曲线,并结合透射电镜对其淬火敏感性进行了研究。结果表明,在等温保温过程中7085铝合金淬火态电导率升高,时效态硬度下降,在中间温度段电导率及硬度变化较快;TTT和TTP曲线的鼻尖温度约为320℃,淬火敏感区间为250~370℃;等温保温过程中,过饱和固溶体分解析出平衡相η,在320℃附近析出速率达到最大,随着等温保温时间的延长,η相聚集并长大,时效后出现大量无沉淀析出区域,导致性能显著下降;在淬火敏感区间,较高的相变驱动力和较大的扩散速率是η相快速析出长大的主要原因。     

淬火冷却速率对6082铝合金力学性能的影响

采用末端淬火(JEQ)实验、使用JMatpro7.0模拟软件并结合硬度、拉伸性能测试以及透射电子显微镜(TEM)观测，研究了轨道交通用6082铝合金的淬火敏感性。结果表明：(1)由JMatpro7.0模拟得到的TTT曲线表明，6082铝合金的淬火敏感温度区间为220~425℃，β和β'相的鼻尖温度为375℃。合金的CCT曲线表明，为了抑制淬火过程中β'(亚稳相)的析出，合金的淬火冷却速率必须大于6℃/s；(2)随着末端淬火距离D的增大6082铝合金的时效态硬度和强度下降，淬透深度为23 mm；(3)随着淬火冷却速率的降低淬火诱导析出相β在异质形核点α-(AlMnFeSi)相上优先析出，在后续的时效过程中β相长大并吸收周围的溶质原子，晶内时效析出强化相β'减少；(4)慢冷过程中，晶界附近的空位浓度降低，晶界的无沉淀析出带(PFZ)变宽。     

6063铝合金挤压型材的TTP曲线测定及其应用研究

通过中断淬火技术测定了6063铝合金挤压型材的时间-温度-性能(TTP)曲线,并通过透射电子显微镜观察其微观组织,采用淬火因子分析法预测不同淬火速率对合金硬度的影响.研究表明,6063挤压型材的TTP曲线鼻尖温度约为360℃,淬火敏感区间为280~410℃.等温保温时,过饱和固溶体分解析出无强化效果的β平衡相,会削弱时效强化效果,在360℃附近的相变速率最快,随着保温时间的延长,粗大β相数量和尺寸增加.为了在较好的时效强化效果和较小的残余应力之间求得平衡,6063挤压型材在线淬火时,在淬火敏感区间的冷却速度最好略大于15℃/s,高于410℃和低于280℃时可适当降低冷却速率.     

7075-H18铝合金板材的淬火敏感性与等温转变行为EI北大核心CSCD

以2 mm厚的7075-H18高强度铝合金板材为研究对象,采用微观组织分析、显微硬度测试、动力学建模与计算相结合的方法,对板材的淬火敏感性、等温相变行为及转变动力学进行系统研究,构建"时间-温度-性能"关系图。结果表明:7075-H18板材具有较高的淬火敏感性。"时间-温度-性能"关系图的鼻尖温度约为350℃,孕育期仅为0.23 s,淬火敏感温度区间为271~404℃,转变量为0.5%的曲线对应的临界线性冷却速率为969.7℃/s,超过了冷模淬火所能达到的冷却速率。板材在等温淬火过程中主要形成粗大的η平衡相,等温时间越长,晶内与晶界的η相尺寸越大,晶界η相越趋于连续分布,且无沉淀析出带变宽。基于实验数据构建的等温转变动力学模型,对7075-H18板材的等温相变过程进行准确预测,板材在350℃等温过程中沉淀相的析出速率最大,等温相变类型为"形核-长大"型相变,相变过程为层片状沉淀相的长大、增厚及互相吞并。理论计算结果与透射电子显微镜下观测到的η相特征以及"时间-温度-性能"关系图相一致。     

均匀化退火后冷却条件对Al-Cu合金组织性能影响

为优化铝合金均匀化退火后的冷却工艺参数,采用动态电阻法、扫描电镜、透射电镜观察、能谱分析和硬度测试等方法,研究了均匀化处理后的冷却条件对Al-4%Cu合金组织性能的影响.获得的电阻率-温度曲线与材料的脱溶行为有良好的相关性.随着均匀化处理后冷却速率的降低,实验合金在冷却过程中会依次析出平衡相θ、亚稳相θ'和θ″.绘制了实验合金的CCT图,确定的脱溶敏感温度区间为500~300℃.选用合适的冷却工艺可以改善合金的组织性能,冷却时间超过1 000 min,合金有较低的硬度和电阻率.当实验合金均匀化后冷却至室温的时间处于19.4~184.1 min时会析出θ″相,导致硬度和电阻率上升,不利于后续的塑性加工,应该尽量避免.     

Zn/Mg比及时效温度对Al-Zn-Mg-Cu系合金析出行为的影响

采用热力学模拟软件中的铝合金模块研究了Al-Zn-Mg-Cu系合金中不同Zn/Mg比及时效温度对析出相GP区及η'相的析出规律的影响。结果表明,GP区含量随Zn/Mg比的增加而降低,低温时效能够促进GP区的形成;而η'相含量随Zn/Mg比的增加略微降低,时效温度对η'相含量影响不大;与120℃相比,合金在160℃时效时η'相含量达到6.5%的时间缩短16 h;在相同温度下时效时,随Zn/Mg比的增加,η'相含量达到6.5%的时间先缓慢增加,当Zn/Mg比大于2.91时则快速增加。合金的淬火敏感性随Zn/Mg比的增加有所降低;随Zn/Mg比从2.46提高到3.20,GP区和η'相的鼻尖温度分别从150℃和330℃降低到140℃和320℃;临界冷却速率随Zn/Mg比的增加而逐渐降低。     

淬火速率对7055铝合金组织和力学性能的影响

通过常温力学性能测试和透射电镜(TEM)研究了淬火速率对7055铝合金组织和力学性能的影响.结果表明,一定时效条件下,合金的力学性能随淬火速率降低而下降.组织观察发现,淬火速率小时,合金在冷却过程中于A l3Zr粒子和晶界非均匀形核析出粗大η平衡相,降低固溶体过饱和程度,削弱时效强化效果.时效时这些粗大η平衡相继续长大并在周围形成无沉淀析出带.晶界无沉淀析出带宽度随淬火速率降低而增大.对合金力学性能下降的原因进行了分析和探讨.     

Mg-10Gd-3Y-0.5Zr合金热压缩动态析出规律

本文定量地研究了Mg-10Gd-3Y-0.5Zr(GW103K)合金在350℃~450℃及10~(-4)s~(-1)~10~(-1)s~(-1)热压缩条件下的动态析出规律。结果表明:固溶处理后的合金在450℃下压缩时,晶内和晶界均无析出相产生,在350℃~400℃热压缩时,有大量不规则颗粒状的析出相产生;析出相主要是β相,平均成分为Mg5.5(Gd_(0.73)Y_(0.27)),大部分分布于再结晶小晶粒的晶界处;析出相的尺寸随温度升高和应变速率的降低而增大,400℃、10~(-4)s~(-1)变形条件下的析出相尺寸能达到1μm以上,而350℃、10~(-4)s~(-1)变形条件下的析出相尺寸在100nm左右;析出相的体积分数随应变量呈非线性增加。不同的变形条件下,析出相体积分数增长趋势不同。350℃下的析出相体积分数在应变量为1.10时达到了3.5%。热压缩过程中,动态析出阻碍位错运动,抑制再结晶晶粒长大,对细化再结晶晶粒起到重要作用。     

Mg-9Al-3Si-0.375Sr-0.78Y合金的热变形行为及本构模型

利用Gleeble-3500热模拟试验机对Mg-9Al-3Si-0.375Sr-0.78Y合金试样进行等温恒应变速率压缩实验,研究其在温度250~400℃、应变速率0.001~10s~(-1)条件下的热变形行为。结果表明:在热变形过程中,峰值应力随着应变速率的降低和温度的升高而减小,且峰值应力对应变速率的敏感性随着变形温度的下降而增强。建立了考虑应变的热变形Arrhenius本构模型,模型精度良好,在300,350℃及0.001~10s~(-1)范围内,模型的平均绝对误差分别为1.57%和1.76%;合金的平均变形激活能为183.58k J/mol,平均应变速率敏感指数为0.1616。热变形过程中,α-Mg相呈现明显的动态再结晶特征,β-Mg₁₇Al₁₂相尺寸减小且分布均匀,初生Mg_2Si相较小。在低温(250~300℃)变形时,动态再结晶仅发生在晶界处。在高温(350~400℃)变形时,初生α-Mg晶粒发生了明显的动态再结晶。随着温度的增加和应变速率的降低,再结晶程度提高,再结晶晶粒逐渐长大。     

6013-T4铝合金不同温度下的动态流变应力及组织演变

采用分离式霍普金森(SHPB)压杆装置进行6013-T4铝合金动态压缩试验,获得温度为25℃、100℃、200℃、300℃、400℃,应变速率为1 000s~(-1)、2 000s~(-1)、3 000s~(-1)、4 000s~(-1)、5 000s~(-1)条件下材料的真应力-真应变曲线,并通过透射电子显微镜(TEM)观测了6013-T4铝合金在不同变形条件下的组织演变。结果表明:6013铝合金有明显的温度敏感性,但是对应变速率的敏感性较弱。应变速率和温度对6013铝合金微观组织的影响显著,位错密度随应变速率的升高而增大,随温度的升高而减小。基于实验数据,求得了6013铝合金Johnson-Cook模型的本构参数并建立其本构模型。与实验结果进行对比,结果表明,所建立的本构模型能够很好地预测6013铝合金的流变应力。     

Study on quenching sensitivity of an Al–Zn–Mg–Cu alloy containing trace amounts of Sc and Zr

The quenching sensitivity of an Al–Zn–Mg–Cu alloy containing trace amounts of Sc and Zr is studied by interrupted quenching experiments. Electrical conductivity of the quenched samples and the hardness of the samples subjected to one-stage and two-stage aging, are measured to construct the time–temperature–transformation (TTT) curves and the time–temperature–property (TTP) curves. It is revealed that the quenching sensitivity of the alloy is mainly influenced by the precipitation of coarse η phases during slow quenching, which preferentially nucleate and grow at grain boundaries and at the Al₃(Sc, Zr) dispersoids that are incoherent with the matrix. The quenching sensitivity increases with the size and quantity of the coarse η phases. The nose temperature is 290 °C for both TTT and TTP curves, where the phase transformation rate is the fastest and the quenching sensitivity is the highest. Compared to one-stage aged samples, two-stage aged samples exhibit lower quench sensitivity due to the reduced transformation rate from η′ phases to η phases after slow quenching. The quenching sensitive temperatures range from 206 to 358 °C for the one-stage aged samples and from 213 to 352 °C for the two-stage aged samples. Moreover, based on the simulated TTT and continuous cooling transformation curves, an optimized quenching process is proposed in the present work.

     

5083铝合金的热变形组织演变及晶粒度模型

通过等温压缩实验、光学显微镜与透射电镜研究了变形温度300~450℃、应变速率0.01~1s-1、真应变0.36~1.2范围内变形条件对5083铝合金热变形组织演变的影响。结果表明:升高热变形温度或降低应变速率均可促进5083铝合金的动态再结晶发生,使变形后5083铝合金位错密度降低,再结晶晶粒尺寸增大;随着应变量的增加,变形后合金的位错密度降低,动态再结晶程度增大。根据唯象理论的指数模型,利用线性回归方法建立了5083铝合金动态再结晶晶粒度模型,模型计算值与实测值吻合良好,平均相对误差仅为4.6%。     

一种新型Al-Zn-Mg-Cu-Zr合金的变形行为研究

通过动态镦粗压缩实验的方法研究了一种新型Al-Zn-Mg-Cu-Zr合金的变形行为。结果表明:Al-Zn-Mg-Cu-Zr合金在350℃以下变形时,由于变形温度较低,在变形过程中发生动态析出行为,合金晶内析出细小沉淀相,对合金的进一步变形不利;当变形温度高于400℃时,合金没有出现动态析出行为;当变形温度继续升高到450℃时,合金出现了动态再结晶和晶粒长大现象。所以,该Al-Zn-Mg-Cu-Zr合金的最佳变形温度为400～420℃,极限变形量为60%。     

The effect of cooling rate on the quench sensitivity of 2618 Al/Al2O3 MMC

Metal matrix composites (MMCs) are materials consisting of metal alloys reinforced with fibers, whiskers, particulates, and wires. Due to their superior mechanical properties, such as low coefficients of thermal expansion and high specific stiffness, they are attractive for many structural and non-structural applications. The most notable production applications are found in the aerospace, automobile, and sports equipment industries. Despite the great potentials possessed by MMCs, there are some concerns regarding the effect of the reinforcements, which are mostly ceramics, on the properties of the matrix alloys. One such property is the quench sensitivity of the matrix material. Heat treatable aluminum alloys are quench sensitive (i. e. their properties and precipitation behavior change with cooling rate or quenchant). The rate of cooling or the type of quenchant used during the fabrication process or the subsequent solution heat treatment affects the mechanical properties of these materials. Therefore, any modification that can alter the quench sensitivity significantly could have important consequences on the heat treatment of the alloys. Thus, the quench parameters may have to be more tightly controlled than for the unreinforced alloy in order to maintain consistent as-quenched properties. In the present study, the quench sensitivity of 2618 Al alloy and its composite containing 10 vol. % Al₂O₃ particles was investigated using hardness measurements and differential scanning calorimetry (DSC). Although 2618 Al is quench sensitive, its quench sensitivity was significantly increased by the addition of Al₂O₃ particles. Also, cooling rate affected the precipitation kinetics and the volume fraction of the precipitate phases formed in both materials.     

Superplasticity in a 7055 aluminum alloy subjected to intense plastic deformation

Abstract

Superplasticity in a 7055 aluminum alloy subjected to intense plastic straining through equal channel angular extrusion (ECAE) was studied in tension over a range of strain rates from 1.4 × 10^-5 to 5.6 × 10^-2 s^-1 in the temperature interval 300 - 450 °C. The alloy had a grain size of ~ 1 μm. A maximum elongation to failure of ~750% occurred at a temperature of 425 °C and an initial strain rate of 5.6 × 10^-4 s^-1, with a strain rate sensitivity coefficient m of about 0.46. The highest m value was ~0.5 at a strain rate of 1.4 × 10^-3 s^-1 and T≥ 425 °C. Moderate superplastic properties with a total elongation of about 435% and m of ~0.4 were recorded in the temperature interval 350 - 400 °C; no cavitation was found. It was shown that the main feature of superplastic behaviour of the ECAE processed 7055 aluminum alloy is a low yield stress and strong strain hardening during the initial stages of superplastic deformation. Comparing the present results with the superplastic behaviour of the 7055 Al subjected to thermomechanical processing (TMP), the highest tensile elongation in the ECAE processed material occurred at lower temperatures because ECAE produces a finer grained structure.