7050高强铝合金淬火敏感性及组织特征(英文)

采用Jominy末端淬火实验研究淬火冷却速率对商用7050铝合金厚板淬火态合金电导率和组织的影响。实验测定距淬火端不同距离合金的淬火态电导率,并进行组织观察。结果表明:在淬火敏感区间范围内,合金的平均冷却速率随着淬火端距离的增加不断降低,而淬火态合金的电导率随着距离的增加不断上升。末端淬火实验棒组织观察显示,厚板表面已发生完全再结晶,1/4和1/2厚度处为部分再结晶组织,淬火诱导晶界析出相逐渐粗化并成链状分布,当距离大于38mm时,发现大量非均质形核淬火析出相,其形核核心主要为Al3Zr弥散相。     

淬火介质对7249铝合金力学性能及晶间腐蚀行为的影响

热轧态7249高强铝合金经固溶处理后分别进行室温空气、PAG淬火液及水淬火处理。通过拉伸实验、OM、SEM及动电位极化曲线等测试手段,研究了不同淬火介质对三级时效后合金力学性能及晶间腐蚀性能的影响。结果表明:随着淬火冷却速率的减小,实验合金基体析出相数量逐渐增多且长大粗化,导致合金时效后力学性能及导电率呈现先增大后下降的趋势,即经PAG淬火处理后,合金综合性能最优;同时合金的腐蚀电流密度和腐蚀速率变小,合金抗晶间腐蚀性能增强。     

高锌Al-Zn-Mg-Cu合金淬火敏感性研究

主要研究不同热处理状态下高锌Al-Zn-Mg-Cu合金的淬火敏感性。结果表明,末端淬火处理后的高锌Al-Zn-Mg-Cu合金棒状试样经人工时效和自然时效后,其120mm处的硬度保留值分别为91.26%和96.25%。人工时效后的试样随着离淬火端距离的增加,沉淀强化相的尺寸增大、密度减小,无沉淀析出带变宽,这些均降低其硬度。GP区为自然时效态合金的主要强化相,而自然时效1680h后试样的淬火端和淬火末端的GP区密度差比较小。因此,该状态的高锌Al-Zn-Mg-Cu合金的淬火敏感性较低。     

7050铝合金热轧板的淬火敏感性

用末端淬火、光学金相显微镜和透射电镜技术研究7050铝合金热轧板的淬火敏感性.结果表明:7050铝合金端淬火试样硬度下降10%的淬透深度约60mm.决定7050铝合金淬火敏感性的本质是析出的η平衡相的尺寸和体积分数,主要发生η相析出的淬火临界平均冷却速率约为40℃/s,此时η相的体积分数约为2.1%.淬火平均冷却速率低于40℃/s,η相析出和粗化一再结晶-Al3Zr非共格化交互影响.     

铸态Al-7Si-0．3Mg合金的连续冷却析出图

采用冷却速率为0．01～3K／s的差示扫描量热法（DSC）和冷却速率更高的淬火膨胀法研究铸态Al-7Si-0．3Mg合金淬火的析出行为。在合金冷却的过程中发生了两种析出反应,高温反应开始于淬火起始温度540℃,低温反应始于400℃左右。3K／s的淬火冷却速率已经显著抑制淬火过程中相的析出。合金T6态的硬度随着淬火速率的增快而增加,这是由合金过饱和固溶度增加而导致的。通过膨胀实验和硬度实验的结果可以估计临界冷却速率大约为60K／s。通过光学显微镜观察淬火态的铸态Al-7Si-0．3Mg合金的显微组织。结果表明：根据淬火冷却速率的不同合金的显微组织由铝一硅共晶组织、铝固溶体枝晶及枝晶间的析出相组成。     

基于末端淬火试验2124铝合金的淬透性

通过Jominy末端淬火实验研究2124铝合金的淬透性。利用温度数据采集、布氏硬度检测、差示量热法(DSC)和透射电子显微镜(TEM)等手段分析淬火冷却速率对时效后第二相析出行为的影响。结果表明:Jominy末端淬火2124铝合金室温水淬硬度下降小于10%的淬透深度大约为50 mm,该位置处合金在222.7～350.0℃温度区间的平均淬火冷却速率大于2.0℃/s;较低的淬火冷却速率致使过饱和的溶质原子和空位损失,导致时效析出相变驱动力不足,显著削弱了时效强化效果。     

淬火速率对含Sc(Zr)高强韧Al-Zn-Mg-Cu合金微观组织和力学性能的影响

通过末端淬火实验(JEQ)、X射线衍射仪(XRD)、扫描电镜(SEM)、透射电子显微镜(TEM)研究一种热挤压Al-Zn-Mg-Cu-Sc-Zr棒材的淬火敏感性。结果表明:随着距离淬火端越远,冷却速率从1800℃/min下降至111℃/min,合金硬度从150 HB下降至133 HB,抗拉强度从430 MPa下降至375 MPa。当冷却速率为131.2℃/min时,合金的硬度为135 HB,合金淬透深度约为93mm。随着冷却速率的降低,端淬时远离淬火端位置,平衡η相先后在晶界、晶内处析出、长大、粗化;时效后,析出的η′强化相的数量减小;时效后,合金内出现无沉淀析出带(PFZ),晶界的PFZ变宽,宽化至160 nm。     

铜元素含量对超高强铝合金力学性能淬火敏感性的影响

采用浸入式末端淬火的方法,结合硬度、电导率测试和相图、连续冷却转变曲线计算,通过电子背散射衍射分析、扫描电子显微镜和透射电子显微镜等微观组织表征方法,研究铜元素含量对超高强AlZn-Mg-Cu合金力学性能淬火敏感性的影响。结果表明：淬火速率从400℃/s降低至70℃/s时,铜含量几乎不影响合金的淬火敏感性;淬火速率从70℃/s降低至4℃/s时,随着铜含量增加,析出驱动力增大,淬火析出相的种类和数量增多、尺寸增大,消耗的相对溶质原子数量增多,合金的淬火敏感性也随之提高;根据晶界及晶内淬火析出相的面积分数差异,发现晶内淬火析出相的数量差异是造成不同合金淬火敏感性差异的主要因素。     

7055铝合金厚板的淬透性

通过末端淬火的方法研究7055铝合金厚板的淬透性,采用透射电子显微镜对微观组织进行分析。结果表明:该合金板材的淬透深度可达45 mm,使其淬透的冷却速率需大于230℃/min;随着冷却速率的减小,淬火过程析出平衡相的数量和尺寸增加,时效后析出的η′沉淀强化相的数量减少,晶界无沉淀析出带宽度增加;在所研究的冷却速率范围内,时效后铝合金板材的硬度、晶界无沉淀析出带宽度与冷却速率的对数均呈线性关系。     

淬火介质及工艺对Al-Zn-Mg-Cu合金腐蚀性能的影响

采用晶间腐蚀、剥落腐蚀、扫描电镜、透射电镜等方法,研究了不同的淬火方式对Al-6.5Zn-2.65Mg-2.2Cu-0.3Sc-0.13Zr锻造态铝合金的腐蚀性能及显微组织的影响.结果表明,空气中自然冷却淬火严重降低了T6时效态合金的抗腐蚀性能.而采用室温水淬的T6时效态合金比室温油淬的时效态合金具有更好的抗剥落腐蚀性能.当预先采用80 ℃×30 s水淬或80 ℃×30 s油淬再室温水淬时,相应T6时效态合金的抗腐蚀性能得到明显改善.预先80 ℃淬火能提高时效态合金的抗剥落腐蚀性能的主要原因是晶界析出相的大小与分布发生了明显的改变.     

Effect of different quenching processes following solid-solution treatment on properties and precipitation behaviors of 7050 alloy

The effects of quenching in different ways following solid-solution treatment on properties and precipitation behaviors of 7050 alloy were investigated by transmission electron microscopy (TEM), scanning electron microscopy (SEM), selected area electron diffraction (SAED), hardness and electrical conductivity tests. Results show that after quenching in different ways, electrical conductivity of the alloy decreases rapidly in the first 48 h of natural aging. The electrical conductivity of 7050 alloy in natural aging state is determined by the size and density of GP zones, and the size of GP zones is the main factor. After natural aging for 70 d, the size of GP zones is 1.8–2.6 nm in matrix of the immersion quenched sample and it is 1.4–1.8 nm in matrix of both water mist and forced air quenched samples. After natural and artificial peak aging, the hardness of the water mist quenched sample is HV 193.6 and its electrical conductivity is 30.5% (IACS) which are both higher than those of the immersion quenched sample. Therefore, water mist quenching is an ideal quenching method for 7050 alloy sheets after solid-solution treatment.     

淬火水温对7050铝合金组织性能的影响

固溶处理是常见的提升7050铝合金综合性能的热处理手段,但由于7050合金存在一定的淬火敏感性,淬火水温是影响其性能的一个重要因素,不同的淬火水温会影响合金获得的固溶体饱和度和析出相尺寸,进而影响合金性能。研究了固溶处理时,冷却水温度对7050铝合金组织性能的影响。结果表明,随着淬火水温的升高,通过EBSD分析得出合金的大角度晶界比例逐渐提升,位错主要集中在大角度晶界和晶界密集的区域,合金中晶界处不断产生析出相并长大,合金硬度呈现先增加后降低的趋势,耐腐蚀性能随着淬火水温的升高持续变差。50 ℃水温淬火时合金具有良好的综合性能,显微硬度为1707.16 MPa,腐蚀电位为?0.927 V。     

Phase equilibria in Ti3Al-Nb alloys at 1000 °C

Titanium aluminides are considered to be the future high-temperature structural materials for turbine applications. Major focus is on α₂Ti₃Al based and γTiAl based alloys. Niobium additions to Ti₃Al alloys is found to improve the room-temperature ductility. Thus phase equilibria in Ti-Al-Nb system is of practical significance with regard to their processing and high-temperature phase stability characteristics. In the present research, four alloys with compositions Ti-22Al-12Nb, Ti-21A1-16Nb, Ti-20Al-20Nb, and Ti-25Al-25Nb (all in atom percent) were equilibrated at 1000 °C for 225 hours and then quenched in water. The quenched alloys were characterized for phase relations by optical microscopy, X-ray diffraction (XRD), and electron probe microanalysis (EPMA). Based on the phase analysis, the ternary isotherm of the Ti-Al-Nb system at 1000 °C was constructed on the Ti₃Al-rich side. The orthorhombic Ti₂AlNb phase was observed in the sample with Ti-25Al-25Nb composition signifying the presence of this phase at 1000 °C.     

Hot-cracking in Aluminium Alloys 7050 and 7010—a Comparative Study

Abstract

Using a recently developed hot cracking test, the cracking susceptibilities of the high-strength aluminium alloys 7010 and 7050 were investigated. The solidification conditions in the test are similar to those encountered in the ingot shell zone during semi-continuous direct chill casting. The influence of grain structure on cracking susceptibility was investigated. Al-Ti and Al-Ti-B grain refining master alloys were added to the melt at various levels in order to obtain grain structures ranging from columnar-dendritic to equiaxed-cellular. Without grain- refiner additions, columnar structures formed which had high cracking susceptibilities; 7010 being marginally less susceptible than 7050. With high grain-refiner additions, equiaxed-cellular grains formed in both alloys, again leading to high cracking susceptibility. Equiaxed-dendritic grains formed at moderate addition levels of grain refiner and were found to be more resistant to hot cracking than either of the other morphologies.     

Optimization of conductivity and strength in Cu-Ni-Si alloys by suppressing discontinuous precipitation

Cu-Ni-Si alloys with and without Ti were solution treated at 980 °C for 1 h and cooled by air cooling and water quenching, after which the specimens were aged at 500 °C. The two alloys showed different aging characteristics with different cooling rates during the aging process. The conductivity of all alloys increased during aging; for alloys that were water quenched, hardness increased at the early stage of aging and then drastically decreased. The air-cooled Cu-Ni-Si alloy without Ti also experienced an increase in hardness, which then decreased during aging, but the air-cooled Cu-Ni-Si alloy with Ti did not show a drastic decrease in hardness during prolonged aging. A combination of yield strength and conductivity of 820 MPa and 42% IACS, respectively, was achieved in the air-cooled Cu-Ni-Si-Ti alloy after solution treatment.     

Influence of Fluidized Bed Quenching on the Mechanical Properties and Quality Index of T6 Tempered B319.2-Type Aluminum Alloys

The current study aimed to investigate the effect of fluidized sand bed (FB) quenching on the mechanical performance of B319.2 aluminum cast alloys. Traditional water and conventional hot air (CF) quenching media were used to establish a relevant comparison with FB quenching. Quality charts were generated using two models of quality indices to support the selection of material conditions on the basis of the proposed quality indices. The use of an FB for the direct quenching-aging treatment of B319.2 casting alloys yields greater UTS and YS values compared to conventional furnace quenched alloys. The strength values of T6 tempered B319 alloys are greater when quenched in water compared with those quenched in an FB or CF. For the same aging conditions (170°C/4h), the fluidized bed quenched-aged 319 alloys show nearly the same or better strength values than those quenched in water and then aged in a CF or an FB. Based on the quality charts developed for alloys subjected to different quenching media, higher quality index values are obtained by conventional furnace quenched-aged T6-tempered B319 alloys. The modification factor has the most significant effect on the quality results of the alloys investigated, for all heat treatment cycles, as compared to other metallurgical parameters. The results of alloys subjected to multi-temperature aging cycles reveal that the optimum strength properties of B319.2 alloys, however, is obtained by applying multi-temperature aging cycles such as, for example, 240 °C/2 h followed by 170 °C/8 h, rather than T6 aging treatments. The regression models indicate that the mean quality values of B319 alloys are highly quench sensitive due to the formation of a larger percent of clusters in Al-Si-Cu-Mg alloys. These clusters act as heterogeneous nucleation sites for precipitation and enhance the aging process.     

Preliminary Examination of the Quenching of Titanium Alloys

From the limited experimental data in the literature, preliminary values were derived for the thermal diffusivity of titanium alloys and for the quenching severity of various mediums used in heat treating them. The thermal diffusivity, under quenching conditions, was found to be approximately 0.006 sq in. per sec. The quenching severity H for brine is approximately 8, for water 4, for oil 0.9, for air 0.08, and for argon 0.02 in.^?1 The quenching severity of the Jominy-Boegehold end quench water jet against titanium alloys appeared effectively infinite. Using these results, graphs were prepared showing ideal round sizes and Jominy positions having cooled conditions equivalent to those at the center and surface of titanium alloy rounds, plates, and sheets quenched in various media.     

温度及加载速率对U-5.7%Nb合金变形行为的影响

研究了淬火和时效2种状态的U-5.7%Nb合金,从室温(20℃)~800℃温度范围的准静态拉伸性能,及合金的变形和断裂行为。结果表明,不论淬火或时效状态的U-5.7%Nb合金,当温度高于200℃后,合金在室温下表现出的二次屈服现象将完全消失,并在400℃温度附近发生脆化,在700℃温度附近表现出明显的超塑性,其中淬火态合金性能的变化尤为明显。并对准静态拉伸、Hopkinson拉伸及爆炸膨胀环3种加载速率下,时效态U-5.7%Nb合金的组织结构进行了对比分析。结果表明,以不同应变速率断裂的时效态U-5.7%Nb合金,断口中心部位的韧窝比边缘部位相对明显,Hopkinson拉伸断口的晶粒大于准静态拉伸断口的晶粒,爆炸速率断裂的合金断口有剪切断裂、边缘开裂及局部夹杂脱落的现象。