Microstructure evolution of Mg-9Gd-2Er-0.4Zr alloy during solid solution treatment

Microstructure evolution of the cast Mg-9Gd-2Er-0.4Zr alloy during solid solution treatment at temperature of 460-520 ℃ for 3-12 h was investigated by using optical microscope（OM）,scanning electron microscope（SEM） and transmission electron microscope（TEM）.The results indicated that the grain size and the shape of second phase were obviously changed with time and/or temperature going on.At 460 ℃ for 3 h,the morphology of the Mg5（GdEr） phase was changed into fragmentized island morphology and the volume faction of the phase decreased.After solution solid treatment at 460 ℃ for 6 h,the Mg5（GdEr） phase was already completely dissolved,but some cuboid-shaped RE-rich phase precipitated.As the temperature increased,the morphology of the Mg5（GdEr） phase was transformed into the same morphology as that at 460 ℃ for 6 h.It was suggested that the microstructure evolution of the alloy during the solid solution treatment was concluded as follows：Mg5（GdEr） eutectic phase→Gd/Er atom diffusing into matrix→spheroidic Mg5（GdEr） phase→cuboid-shaped RE-rich phase→grain boundary immigration.

Effect of two-step solid solution on microstructure andδphase precipitation of Inconel 718 alloy

Inconel 718 is the most popular nickel-based superalloy and is extensively used in aerospace,automotive,and energy indus-tries owing to its extraordinary thermomechanical properties.The effects of different two-step solid solution treatments on microstructure andδphase precipitation of Inconel 718 alloy were studied,and the transformation mechanism fromγ″metastable phase toδphase was clarified.The precipitates were statistically analyzed by X-ray diffractometry.The results show that theδphase content firstly increased,and then decreased with the temperature of the second-step solid solution.The changes in microstructure andδphase were studied by scanning electron microscopy and transmission electron microscopy.An intragranularδphase formed in Inconel 718 alloy at the second-[100]_(δ)[011]γ step solid solution temperature of 925℃,and its orientation relationship withγmatrix was determined as//and(010)_(δ)//(111)γ.Furthermore,the Vickers hardness of different heat treatment samples was measured,and the sample treated by second-step solid solution at 1010℃ reached the maximum hardness of HV 446.84.

Effects of on-line solution and off-line heat treatment on microstructure and hardness of die-cast AZ91D alloy

The effects of on-line solution, off-line solution and aging heat treatment on the microstructure and hardness of the die-cast AZ91D alloys were investigated. Brinell hardness of die-cast AZ91D alloy increases through on-line solution and off-line aging treatment but decreases after off-line solution treatment. By X-ray diffractometry, optical microscopy, differential thermal analysis, scanning electron microscopy and X-ray energy dispersive spectroscopy, it is found that the microstructures of the die-cast AZ91D magnesium alloy before and after on-line solution and off-line aging are similar, consisting of α-Mg and β-Al12Mg17. The precipitation of Al element is prevented by on-line solution so that the effect of solid solution strengthening is enhanced. The β-Al12Mg17 phases precipitate from supersaturated Mg solid solution after off-line aging treatment, and lead to microstructure refinement of AZ91D alloy, so the effect of precipitation hardening is enhanced. The β-Al12Mg17 phases dissolve in the substructure after off-line solution treatment, which leads to that the grain boundary strengthening phase is reduced significantly and the hardness of die cast AZ91D is reduced.

Characterization of a Mg_(95.5)Zn_(1.5)Y_(3)alloy both containing W phase and LPSO phase with or without heat treatment

The influence of solid solution treatment on the microstructure and corrosion resistance of as-cast Mg_(95.5)Zn_(1.5)Y_(3) alloy is characterized.The microstructure of the as-cast Mg_(95.5)Zn_(1.5)Y_(3) alloy mainly consisted ofα-Mg,W(Mg_(3)Zn_(3)Y_(2))phase,and the long period stacking ordered(LPSO)(Mg_(12)ZnY)phase.After solid solution treatment,most of the W phase disappears gradually with increasing solution treatment time,with only a small amount of W phase distributed as particle.The LPSO phase slightly dissolved into substrate,and its morphology transitions from blocky shape to rod shape.Solid solution treatment of Mg_(95.5)Zn_(1.5)Y_(3) exhibits excellent corrosion resistance,because the Y and Zn atoms became enriched in the matrix and the changed morphologies of the LPSO and W phases were modified through heat treatment.The alloy created with solid solution treatment at 520 ℃ for 10 hours exhibits corrosion potential of−1.419 V,suggesting a significant improvement in corrosion performance.

Deformation-Induced Large Ductility of Super Saturated Solid Solution Fe-Cu Alloy

The mechanical properties of super saturated solid solution Fe60Cu40 alloy has been investigated using compression test. The results show that the grain precipitation and phase transformation occurs during compressive deformation resulting in large work-hardening ability, high strength and large ductility. Our results demonstrate that this novel architecture offers a design pathway towards a new generation of strong materials with large ductility.

Incoloy 028挤压管析出相分析及解决途径

Incoloy 028合金在热加工过程中质量控制难度较高,特别是大尺寸棒坯的中心部位,易产生析出相,会影响后续加工的成品管质量。本文以φ320mm棒坯经挤压、冷轧生产工艺为例,采用SEM、EDS、XRD等方法分析了028合金中的析出相微观形貌和结构。试验结果表明:原材料的质量会影响成品管的质量,固溶处理可以消除028合金挤压管中的析出相,对挤压荒管进行固溶处理是十分必要的。800℃至850℃下进行热处理,028合金析出相为Cr_(23)C_6和σ相;850℃至1050℃下进行热处理,028合金析出相为σ相;1100℃进行热处理可以消除析出相。

N08028合金油井管的固溶及冷作硬化工艺研究

分析了N08028合金油井管管坯原始组织形貌、热挤压及后续固溶处理对组织形貌的影响,同时研究了N08028合金的冷作硬化工艺。试验结果表明:管坯的原始析出相在热挤压过程中可以溶解,热挤压会产生新的析出相,需通过固溶处理消除;固溶处理后的N08028合金油井管需通过冷作硬化使其力学性能达到标准要求。在冷作硬化过程中N08028合金油井管的屈服强度及抗拉强度与断面收缩率基本呈线性关系,并建立了应力-应变方程。

Microstructure of Al-Si-Mg alloy with Zr/Hf additions during solidification and solution treatment

In this study,the morphology,composition and evolution of intermetallics in Al-7Si-0.3Mg,Al-7Si-0.3Mg-0.47Hf,Al-7Si-0.3Mg-0.16 Zr and Al-7Si-0.3Mg-0.14Zr-0.44Hf alloys were characterized by optical microscope(OM),scanning electron microscope(SEM)with energy-dispersive spectrometer(EDS) and transmission electron microscope(TEM).The AlSiZr,AlSiHf and AlSiZrHf phases are formed with additions of Zr and/or Hf in base alloy during solidification,especially the AlZrHf primary particles.The three-dimensional morphology of the AlZrHf particle evolves from 10-polyhedron-like to compressed cube-like during solidification.The new AlZrHf phase experiences partial dissolution after solution treatment,while the others remain in the initial morphology.High Si contents lead to form thermally stable Zr/Hfrich precipitates in Zr/Hf-containing alloys during solution treatment,especially the nanobelt-like Si2Zr,Si2Hf and Si2(Zr,Hf) precipitates.Particular orientation relationships and the growth mechanism are identified.The finding of the work broadens the elevated temperature application of Al-Si-Mg in modern automotive aluminum engine.

Evolution in microstructure and mechanical properties during back-annealing of AlMnFeSi alloy

An Al-Mn-Fe-Si model alloy was subjected to two homogenization treatments, to achieve materials with different levels of Mn in solid solution and dispersoid densities, followed by cold rolling and back-annealing. Characterization of homogenization and deformation structures with respect to the effect of different microchemistries and strains on the structures was performed. Time-temperature-transformation （TTT） diagram with respect to precipitation and recrystallisation as a basis for analysis of the degree of concurrent precipitation was established. The TTT-diagram shows a strong effect of Mn concentration in solid solution and dispersoid density on the softening behavior. Recrystallization which finishes without the effect of concurrent precipitation results in an even, fine and equiaxed grain structure. Precipitation prior to or during recrystallization （concurrent） does retard the softening kinetics and leads to a coarse grain structure. However, the effect also depends on the duration of recrystallization and amount of precipitation. Recrystallization proceeding over a long time combined with a large amount of concurrent precipitation has a strong effect, otherwise the effect will be limited. Pre-existing fine and dense dispersoids （mean size 0.1 μm） before back-annealing do also lead to a coarse grain structure after recrystallization no matter whether additional concurrent precipitation occurs.

固溶处理对铸造Al-Si合金相选择再结晶的影响

相选择再结晶在Al-Si合金中基于应变分配原理实现对软相进行再结晶、硬相进行回复从而球化硅相和细化铝相。相选择再结晶处理后合金呈现出高的加工硬化率和伸长率。固溶处理是实现铝合金强韧化的重要环节,与相选择再结晶互相影响。一方面,初始组织对相选择再结晶的应变分配有一定影响;另一方面铝合金固溶过程会影响析出强化作用。因此,本文探究铸造Al-7Si-0.65Mg合金固溶过程中共晶硅相的形貌对相选择再结晶的影响,结合时效析出实现合金的强韧化。结果表明,0.5 h短时间固溶处理可以保持相选择再结晶合金中清晰且不分散的共晶硅颗粒骨架状结构,同时增加基体中Si和Mg含量促进强化相Mg2Si析出,使合金屈服强度达到300 MPa,断后伸长率为9.5%,显著优于传统T6态。

固溶处理时间对Al-10SiM合金摩擦学性能的影响

生物柴油应用引起发动机润滑环境的恶化,加速了活塞常用材料Al-10Si合金的腐蚀磨损,使其发生早期失效。因而,设计、铸造了一种Al10Si0.25Cu5Mg0.25Sn0.15Sc0.15Ti新型Al-Si系合金(简称Al-10SiM合金),随后在510℃下对其分别进行8、12、16和20 h的固溶处理,以研究不同时间的固溶处理对Al-10SiM合金物相结构、显微组织、维氏硬度和在模拟生物柴油发动机活塞运行工况下摩擦学性能的影响。结果表明:随固溶处理时间从8 h增至20 h,Al-10SiM合金中的Mg2 Si相消失,Al 3 Sc与Mg2 Sn相形成后又消失,析出相尺寸先减小后长大,析出相分布弥散、均匀性先变好后变差;维氏硬度在16 h时达到最高值162.6 HV,在20 h时又降至130.8 HV。在法向载荷为10和15 N下,当固溶处理时间为8~16 h时,Al-10SiM合金的摩擦系数和磨损率降低,固溶处理时间为20 h时又上升,在固溶处理时间为16 h时获得最佳的减摩抗磨性能,且它们在摩擦中均发生了不同程度的粘着磨损、磨粒磨损和疲劳磨损。

粉末冶金法制备Cu-Ni-Si合金的组织和性能

以单质Cu粉、Ni粉和Si粉为原料,通过热压烧结方法制备Cu含量为94(质量分数,%),Ni、Si质量比为4∶1的Cu-Ni-Si合金。经过900℃固溶处理2 h和450℃时效处理4 h后,采用金相显微镜、扫描电镜、能谱分析和X射线衍射仪对合金的显微组织和相组成进行了分析。结果表明:合金中只有δ-Ni2Si相形成,且δ-Ni2Si相的组织形貌及分布状态对合金的力学性能和导电率起着决定性的作用;经过时效处理后,析出的δ-Ni2Si相使合金的导电率和维氏硬度都明显提高。

不同固溶处理对Cu-Cr系合金组织和性能的影响

热处理工艺调控是提升Cu-Cr系合金性能的有效方法。Cu-Cr系合金的固溶工艺大多选择温度较低的Cu-Cr两相区进行,导致Cr相固溶程度不完全,抑制后续析出强化效果。本研究提出采用高温单相区固溶工艺改善析出强化效果,主要研究不同固溶工艺(Cu-Cr两相区(950℃,4 h)和Cu单相区(1050℃,6h))对Cu-Cr系合金组织和性能的影响。采用电子探针(EPMA)对两种固溶工艺后的元素分布进行表征,并对峰值时效态合金的微观结构采用XRD和TEM进行表征分析。结果表明:与两相区固溶相比,单相区固溶后铸态Cr相充分固溶,时效过程中更多纳米Cr相弥散析出;合金力学性能相比两相区固溶后峰值时效态有较大提升,其中屈服强度提升29.3%,抗拉强度提升25.6%,而导电率并未明显下降。强度理论计算结果表明,析出强化所贡献的屈服强度增量为323.4 MPa,贡献56.9%,析出强化是本研究中最主要的强化机制。

固溶处理对2205双相不锈钢点蚀性能的影响

采用金相显微镜、电子能谱分析仪、透射电子显微镜、FeCl3溶液浸泡法和循环极化曲线法研究了固溶处理对2205双相不锈钢组织和点腐蚀性能的影响。结果表明,经1050℃×2h水冷固溶处理后,实验钢中α和γ两相体积含量约各占一半,组织均匀且细化,在6%FeCl3溶液中的临界点蚀温度为45℃,在3.5%NaCl溶液中的点蚀电位Eb和保护电位Ep均为1028mV,表现出良好的耐点蚀性能。经950℃固溶处理后组织中析出σ相,σ相导致其抗点蚀性能下降。

稀土微合金化及其对钒铌沉淀相析出规律的影响

稀土在钢中有一定的固溶量 ,可达 10 -5～ 10 -4 数量级 ,起微合金化作用 。

Sb变质对Mg-6A1-1Zn-0.7Si镁合金热处理组织和力学性能的影响

通过金相、扫描电镜(SEM)、X射线衍射分析(XRD)和差热分析(DSC)等手段,研究Sb变质对Mg-6Al-1Zn-0.7Si镁合金热处理组织和力学性能的影响,尤其是对合金固溶处理组织的影响。结果表明:固溶处理可以变质Mg-6Al-1Zn-0.7Si镁合金铸态组织中的汉字状Mg2Si相,使Mg2Si相从汉字状变为短杆状和条块状,并且添加0.4%Sb到实验合金中可使固溶处理变质汉字状Mg2Si相的效果提高。也正是由于固溶处理可以使实验合金组织中的汉字状Mg2Si相变质,使得Mg-6A1-1Zn-0.7Si合金时效处理后获得了较铸态更高的的抗拉性能和抗蠕变性能,并且添加0.4%Sb可以进一步增强热处理对性能的改善作用。

热处理对AZ91D镁合金组织及力学性能的影响

结合Mg-Al二元相图,研究不同时间固溶处理对AZ91D镁合金力学性能的影响,以及固溶时效处理后镁合金组织、性能的变化.结果表明,随着固溶处理时间的延长,AZ91D镁合金中的β相逐渐分解并溶入α相中,固溶处理5 h后,β相完全分解;继续延长固溶处理时间,AZ91D镁合金中的合金元素在扩散机制的作用下趋向均匀.研究还发现,AZ91D镁合金经415℃×10 h和415℃×24 h固溶处理后力学性能最优,且经时效处理后这2组工艺仍具有最优的力学性能.

固溶时效Mg-4Y-3Nd合金析出相与基体的微观结构

用XRD衍射和透射高分辨HTEM方法分析Mg-4Y-3Nd合金在固溶处理525℃×8 h、时效温度250℃、时效时间16 h状态下的显微组织、析出相的点阵结构和基体点阵常数变化。结果表明:经过固溶时效的Mg-4Y-3Nd合金的显微组织由α-Mg固溶体、析出相Mg24Y5、Mg41Nd5和Mg14Nd2Y组成。析出相在晶内和晶界同时析出,晶内析出相形状为块状或短杆状,呈弥散分布,晶界上析出相呈三角形为链状分布,时效析出相Mg14Nd2Y与基体为半共格界面位相关系。随着析出相的生成,基体的点阵常数变大,同一晶面的衍射角(2θ)减小,晶面间距增大。

部分固溶处理对AZ91D镁合金微观组织及力学性能的影响

对AZ91D镁合金进行部分固溶处理,研究其热处理后的组织和性能.结果表明:温度较低时,合金的性能随时间变化不明显.升高温度,硬度随时间延长逐渐降低,而抗拉强度和延伸率逐渐增加.当保温时间一定时,硬度随温度的升高逐渐降低,抗拉强度和延伸率则逐渐增加.部分固溶处理后,晶界处硬脆相β-Mg17Al12部分溶入基体,同时由原来的网状分布变成岛状分布.硬脆相的减少,使得合金的硬度有所下降,但高于完全固溶处理后的硬度,而硬脆相形态的改变,又提高了材料的抗拉强度和延伸率.升高温度或延长保温时间,合金的脆性断裂倾向减小,拉伸断口呈现出较多的韧窝,对大幅度提高合金的力学性能极为有利.

热处理过程中Mg-8Gd-3Y-1Nd-0.5Zr合金的组织演变及性能

采用透射电镜、扫描电镜、能谱分析、X射线衍射及力学性能等测试手段,研究热处理工艺对水冷铸造的Mg-8Gd-3Y-1Nd-0.5Zr(质量分数)合金显微组织、力学性能和耐腐蚀性能的影响。合金铸态显微组织由α-Mg、Mg(Gd,Y)相、富Zr小颗粒相和β-Mg_(24)Y_5网状共晶组成。在520℃固溶24 h后,合金中共晶相固溶进基体,固溶演变过程为α-Mg+β-Mg_(24)Y_5相+Mg(Gd,Y)→过饱和α-Mg固溶体+Mg(Gd,Y)相。225℃时效,合金的析出序列为Mg(S.S.S.S)→β″(DO19)→β′(CBCO)→β_1(FCC)→β(FCC),时效24 h达到峰时效态,合金的室温抗拉强度达到231MPa,伸长率为3.4%。时效处理能提高合金耐腐蚀性能,225℃时效72 h时合金析出稳定β(FCC)相,平均析氢速率最小,为0.22 mL/(cm^2·h),合金的耐腐蚀性能最强。