2219铝合金的淬火敏感性

通过分级淬火方法测定了2219铝合金的时间-温度-性能(TTP)曲线。结果表明:合金TTP曲线的鼻尖温度为440℃,淬火敏感温度区间为300~480℃;等温保温时,过饱和固溶体分解析出相粒子,在440℃附近,析出相(主要为θ平衡相)的析出速率达到最高;随着时间的延长,晶内θ平衡相数量增加、尺寸变大,经时效后晶内析出相θ'不均匀分布,导致强化效果显著降低,晶内出现无沉淀析出区;鼻尖温度的高相变驱动力和较快的扩散速率是θ相析出和长大的主要原因,建议在淬火敏感区间应加快淬火冷却速率避免平衡相的析出,而高于淬火敏感区间温度时可适当降低冷却速率减小热应力的影响。     

2219铝合金的淬火敏感性北大核心CSCD

通过分级淬火方法测定了2219铝合金的时间-温度-性能（TTP）曲线。结果表明：合金TTP曲线的鼻尖温度为440℃,淬火敏感温度区间为300-480℃;等温保温时,过饱和固溶体分解析出相粒子,在440℃附近,析出相（主要为θ平衡相）的析出速率达到最高;随着时间的延长,晶内θ平衡相数量增加、尺寸变大,经时效后晶内析出相θ＇不均匀分布,导致强化效果显著降低,晶内出现无沉淀析出区;鼻尖温度的高相变驱动力和较快的扩散速率是θ相析出和长大的主要原因,建议在淬火敏感区间应加快淬火冷却速率避免平衡相的析出,而高于淬火敏感区间温度时可适当降低冷却速率减小热应力的影响。     

6061铝合金的淬火敏感性研究

采用中断淬火/时效处理获得时间-温度-性能(TTP)曲线,结合透射电镜(TEM)微观组织研究了6061铝合金的淬火敏感性。结果表明,6061铝合金TTP曲线的鼻尖温度约为340℃,中温区(230~445℃)淬火敏感性较高,而高、低温区淬火敏感性较低。合金在鼻尖温度保温过程中,粗大平衡相依附于富铁相(AlFeSi)粒子不均匀形核析出,减小了基体中溶质原子溶度,削弱了后续时效强化效果。适当提高淬火敏感区的冷却速率和降低高、低温区的冷却速率,这既可保证合金较佳的力学性能,又减小淬火应力。     

7050铝合金的TTP曲线

通过分级淬火方法获得7050铝合金的时间-温度-性能(TTP)曲线.结果表明:合金TTP曲线的鼻尖温度为330 ℃,淬火敏感温度区间为240～420 ℃;等温保温时,过饱和固溶体分解析出第二相粒子,在330 ℃附近,第二相(主要为η平衡相)的析出速率达到最高;随着时间的延长,晶内η相数量增加、尺寸变大,时效后粒子周围出现无沉淀析出区,导致强化效果显著降低;晶界处η相粒子粗化,由不连续分布形貌转变为连续分布形貌,无沉淀析出带宽化;鼻尖温度的高相变驱动力和较快的扩散速率是η相析出和长大的主要原因,建议在淬火敏感区间应加快淬火冷却速率避免平衡相的析出,而高于淬火敏感区间温度时可适当降低冷却速率减小热应力的影响.     

1933铝合金锻件的TTP曲线

利用分级淬火的方法测定了1933铝合金锻件硬度及电导率的时间—温度—性能(time-temperature-property,TTP)曲线。结果表明,TTP曲线呈"C"形,淬火敏感区间为265～355℃(200 s内硬度值下降10%),TTP曲线的"鼻尖"温度大约在310℃,在此温度下,硬度下降10%的临界时间为100 s。微观组织观察表明,在敏感区间内,平衡相η在晶界及Al3 Zr与基体的界面上优先形核析出,并快速长大,导致合金过饱和度的下降,降低了时效强化的效果。与目前公布的其他Al-Zn-Mg-Cu系合金的TTP曲线对比,1933铝合金的"鼻尖"温度低,临界时间长,淬火敏感区间窄,因此淬火敏感性较低。     

7050铝合金淬火敏感性研究和微观组织分析

通过分级淬火方法测定了7050铝合金的TTT曲线,采用TEM和JMA方程等分析手段研究了固溶、等温淬火和时效过程中微观组织的演变规律及其动力学特性.结果表明,合金TTT曲线的鼻尖温度在330℃附近,淬火敏感区间为300~380℃,高温区(400~450℃)淬火敏感性低于低温区(210~270℃);等温保温过程中过饱和固溶体主要析出以Al3Zr粒子为形核核心的片层状h平衡相及少量针状S相,随保温时间延长析出相体积分数快速增加,同时在晶界排列变得连续而粗化、无沉淀析出带(PFZ)宽化,在远离鼻尖的温度下保温合金析出速率减慢,在晶界排布连续化和粗化程度降低;JMA方程中反映析出相形态的常数n在0.50~0.65的范围内,析出相特征以片层状相为主、针状相为辅.     

6351铝合金的淬火敏感性

采用分级淬火的实验方法,结合合金时效态硬度和淬火态电导率的测试拟合得到6351合金的TTP和TTT曲线,并采用透射电镜对6351合金的淬火敏感性进行研究.结果表明,当6351合金在相同温度下等温时,随着保温时间延长,淬火态电导率呈上升趋势,时效态硬度呈下降趋势.透射电镜分析发现,在等温初期,过饱和固溶体分解形成针状的β”相;随着保温时间延长,逐渐形成棒状β'相和片状β相.TTT和TTP曲线的鼻温为360℃,淬火敏感温度区间为230～430℃.在鼻温附近等温相转变最快,低温区相转变次之,高温区最慢.淬火因子分析结果表明,要获得最佳的力学性能,淬火敏感温度区间的冷却速率需大于15℃/s.     

7055铝合金的TTP曲线及其应用

采用分级淬火的方法测定了7055铝合金的温度—时间—性能(TTP)曲线,并结合合金实际淬火冷却曲线通过淬火因子分析方法预测了合金的硬度。结果表明,合金TTP曲线的“鼻尖”温度大约为355℃,淬火敏感温度区间为210~420℃。淬火因子分析方法预测的合金硬度值和实测值吻合较好,淬火敏感温度区间的冷却速率对合金硬度有决定性影响。根据理论计算认为,要获得最大硬度,淬火敏感温度区间的平均冷却速率需大于500℃/s。     

淬火介质对7050铝合金末端淬特性的影响

采用室温水和浓度为20%的PAG水溶液(聚烷撑二醇聚合物)作为淬火介质进行Jominy末端淬火实验,用于评价7050铝合金淬透性;监测合金固溶和淬火过程中的升温速率和冷却速率,测定距淬火端不同距离的合金的淬火态电导率和时效态硬度,观察室温水淬火试样不同位置晶内淬火析出相.结果表明:采用室温水和20%PAG进行末端淬火时,合金的淬透深度分别约为65和40mm;采用PAG淬火可使合金温度快速通过淬火敏感区间,同时在淬火敏感区间外降低合金的冷却速率,使试样淬火端和中间部位合金的温度差减小.随着距淬火端距离的增加,淬火诱发析出的η平衡相的尺寸和体积分数增加,无析出区宽化.     

6082铝合金的淬火特性及微观组织研究

采用末端淬火和中断淬火方式,结合透射电镜(TEM),研究了6082铝合金的淬火特性及微观组织变化特征。结果表明：在末端淬火试验条件下,6082铝合金的淬透深度为15-20 mm;淬火敏感区间的平均冷却速率达20 ℃/s时,合金时效后形成细小弥散的β″相,无沉淀析出带(PFZ)窄小。在中断淬火的高温保温过程中,几乎没有β平衡相的析出,时效后获得了较高的硬度;在中温保温过程中,β平衡相因消耗周围的溶质原子而快速形成并长大,导致时效后合金性能大幅度下降;低温保温过程中,β平衡相形成缓慢,随时间增加,析出数量增多并长大,影响后续时效强化效果。合金在慢冷和保温过程中,析出的β平衡相大多是以富铁相颗粒作为不均匀形核的核心,这是造成合金淬火敏感性高的原因之一。     

Quenching sensitivity and heterogeneous precipitation behavior of AA7136 alloy

The quenching sensitivity of AA7136 alloy was investigated by time−temperature−property (TTP) diagrams, and the heterogeneous precipitation behavior during isothermal holding was investigated using scanning electron microscopy, scanning transmission electron microscopy and high resolution transmission electron microscopy. Based on 99.5% TTP diagram, the nose temperature is determined to be about 346 °C with the transformation time of about 0.245 s. The precipitation of η (MgZn₂), T (Al₂Zn₃Mg₃), S (Al₂CuMg) or Cu−Zn-rich Y phases can be found depending on isothermal holding temperature and time, and it is described in a time−temperature−precipitation diagram. The size and area fraction of isothermal holding induced phase particles increase, which results in the decrease of hardness of samples after aging. The quantitative contribution to loss of hardness by grain boundaries/subgrain boundaries and dispersoids in the matrix is discussed based on the amount of heterogeneous precipitation related to them.     

Hardening precipitation in a Mg–4Y–3RE alloy

Early stages of precipitation in a Mg–Y–Nd based alloy aged at 150 °C have been studied using TEM and small angle X-ray scattering (SAXS). The former brings information concerning nature, morphology and size of precipitates, and the latter adds qualitative and quantitative information concerning populations of precipitates in terms of size and volume fraction. Precipitation at 150 °C involves formation of DO₁₉ monoplanar precipitates, which further develop into the β″ and β′ phases having platelet and globular morphologies, respectively. TEM observations on samples aged at 150 °C reveal the formation mechanism of the bco-β′ structure by the ordering of monoplanar DO₁₉-β″ precipitates. Additional examinations at 250 °C revealed the DO₁₉-β″→bco-β′ transformation, as well as β₁ precipitates. Estimation of the volume fraction deduced from SAXS is discussed on the basis of the TEM results.     

Formation of the structure and properties of β-type titanium alloy upon thermomechanical treatment

The rapid quenching of β-type titanium alloy from 800°C and cold deformation by drawing (ε = 24%) leads to the formation of a cellular-banded structure with a cell size of 200 × 400 nm and high density of dislocations (~5 × 10¹⁴ m^–2). During subsequent aging at 450°C, the decomposition of the β-phase occurs with a heterogeneous precipitation (at dislocations) of plates of the α phase with a thickness of 10–30 nm and length of 50–100 nm. The small size and high density of α crystals (5 × 10²¹ m^–3) provide a substantial increase in the strength characteristics of the alloy.     

Effect of heat treatments on structural,microstructural and mechanical properties of Al 2017 alloy

The effect of ageing at 300°C before and after quenched at two temperatures of 180 and 280°C on the Al 2017 alloy was studied. The structural properties were investigated using X-ray diffraction; the microstructural evolution was investigated using scanning electron microscopy and microhardness measurement for the mechanical properties. After various states of ageing, the Al–Cu–Fe alloy shows significant changes in the microstructure and mechanical behavior. After ageing, the microstructure of the matrix consisted of a three solid solution of α-Al–Cu-Fe, β-AlFe and θ-A2Cu phases precipitations. After two-step heat treatment (quenching and ageing), the alloy reveals the formation of β and θ phases precipitates. After ageing at 300°C of original sample, the alloy reveals higher β precipitates, corresponding to the minimum value of microhardness, the volume fraction of this precipitates becomes higher. On the other hand, the TTT curves for the discontinuous and continuous precipitation reaction in this alloy have been suggested.     

Phase and structural transformations in the alloy on the basis of the orthorhombic titanium aluminide

Phase and structural transformations in the Ti-24.3 Al-24.8 Nb-1.0 Zr-1.4 V-0.6 Mo-0.3 Si (at %) alloy that take place during heating in the temperature range of 700–1050°C have been investigated. The temperature ranges of existence of the O + β, O + β + α₂, β + α₂, and β phase fields have been established. A scheme of the relationships between the volume fractions of the O, β, and α₂ phases depending on the temperature of heating of the alloy have been investigated. The formation of an ordered incommensurate ω (V _ω) phase has been revealed in the alloy during quenching from 900°C. The existence of a correlation between the hardness properties and changes in the phase composition and morphology of particles precipitating in the alloy has been shown.     

Influence of TiB2 nanoparticles on elevated-temperature properties of Al-Mn-Mg 3004 alloy

Two contents (1.5% and 3%) of TiB₂ nanoparticles were introduced in Al-Mn-Mg 3004 alloy to study their effects on the elevated-temperature properties. Results show that TiB₂ nanoparticles were mainly distributed at the interdendritic grain boundaries with a size range of 20–80 nm, which is confirmed by transmission electron microscopy (TEM) and X-ray diffraction (XRD). Therefore, the volume fraction of the dispersoid free zones is greatly reduced and the motion of grain boundaries and dislocations is inhibited more effectively at elevated temperature. After peak precipitation heat treatment, the yield strengths in the alloy with 3% TiB₂ addition at room temperature and 300 °C were increased by 20% and 13% respectively, while the minimum creep rate at 300 °C was reduced to only 1/5 of the base alloy free of TiB₂, exhibiting a considerable improvement of elevated-temperature properties in Al-Mn-Mg alloys.     

Computation of synthetic surface heat transfer coefficient of 7B50 ultra-high-strength aluminum alloy during spray quenching

According to inverse heat transfer theory, the evolutions of synthetic surface heat transfer coefficient (SSHTC) of the quenching surface of 7B50 alloy during water-spray quenching were simulated by the ProCAST software based on accurate cooling curves measured by the modified Jominy specimen and temperature-dependent thermo-physical properties of 7B50 alloy calculated using the JMatPro software. Results show that the average cooling rate at 6 mm from the quenching surface and 420–230 °C (quench sensitive temperature range) is 45.78 °C/s. The peak-value of the SSHTC is 69 kW/(m²·K) obtained at spray quenching for 0.4 s and the corresponding temperature of the quenching surface is 160 °C. In the initial stage of spray quenching, the phenomenon called “temperature plateau” appears on the cooling curve of the quenching surface. The temperature range of this plateau is 160–170 °C with the duration about 3 s. During the temperature plateau, heat transfer mechanism of the quenching surface transforms from nucleate boiling regime to single-phase convective regime.     

Effect of quenching temperature on structure and properties of titanium alloy: Structure and phase composition

X-ray diffraction analysis and transmission and scanning electron microscopy have been used to study regularities of the formation of structure and phase composition of a VT16 alloy during its quenching. The formation of an athermal ω phase in the VT16 alloy with the initial (α + β) structure during quenching of the alloy from 800°C was found to be possible. Quenching temperatures (T _q) at which various metastable phase compositions, such as the metastable β solid solution, β + α″ + ω, β + α″, and α″ martensite, are formed have been determined to be 750, 800, 750–850, and ≤850°C, respectively. Dependences of variations in the volume fractions of phases were plotted. It has been shown that, at quenching temperatures close to the β-transus, the active growth of β-phase grains takes place at the expense of a decrease in the α-phase volume fraction.     

Precipitation during homogenization cooling in AlMgSi alloys

Precipitation during the industrial cool down takes place predominantly above 300 °C in the EN AW-6082 and 6005 alloys. The phase precipitation throughout cooling is equilibrium β phase. A considerable capacity is retained after the cool down for further precipitation during a subsequent heating cycle. The β-Mg₂Si is once again the predominant phase that forms during a scan heating cycle employed in exactly the same manner with the industrial billet preheating operation. The precipitation in the 6060 alloy, on the other hand, occurs predominantly below 300 °C with additionally β′-Mg₂Si particles formed below 200 °C.