时效路径对Al-0.7Mg-0.5Si-0.2Cu-0.5Zn合金沉淀析出行为的影响

利用DSC、TEM、拉伸实验以及硬度测试等方法系统研究了时效路径对高Mg/Si比Al-Mg-Si-Cu-Zn合金沉淀析出行为的影响。结果表明,固溶淬火态和预时效态合金在非等温时效过程中β″相的析出激活能分别为80.1和64.5 kJ/mol;在等温时效过程中表现出不同的时效硬化和组织演化行为,其中固溶淬火态合金时效硬化速率较快,但最终2种路径处理的合金峰值硬度和强度基本相同;但经预时效处理的合金,峰时效态延伸率和应变硬化速率以及过时效阶段硬度降低速率均较高。与此同时,预时效态合金还可析出大量复合溶质原子团簇,虽然在高温等温时效时会进一步长大,但使得欠时效、峰时效和过时效态合金的沉淀相尺寸呈多尺度特征,而固溶淬火后直接等温时效的不同状态合金却无此特征。时效路径并未改变合金沉淀析出序列,但对沉淀相形核、长大速率影响显著,据此提出了时效路径对沉淀相形核和长大过程影响的模型示意图。     

6016铝合金汽车板材预时效处理工艺研究

研究了预时效处理工艺对汽车用6016铝合金板烘烤硬化性能的影响,试验结果表明,经过预时效处理可明显改善人工时效过程中合金软化现象。160℃、7 min预时效处理后板材硬度值高于T4态且呈现增长趋势,有效的抵消了自然时效过程中的合金软化现象。DSC结果表明,预时效处理可加快Mg2Si相析出速度,提高人工时效效果。拉伸结果表明,预时效后烤漆试样屈服强度达到321 MPa,相比自然时效烤漆试样硬度提高了60 MPa,降低自然时效对板材烤漆硬化性能的影响。对6016铝板材采用固溶处理+预时效+烤漆硬化工艺流程,有利于获得良好的板材冲压成形性能以及烘烤硬化处理效果。     

半固态挤压铸造A356合金在热处理过程中的组织和性能演化（英文）

半固态挤压铸造的A356合金首先在540℃下进行固溶处理,随着固溶温度升高,Mg和Si原子逐渐溶解于基体中,并产生了固溶强化作用。抗拉强度、延伸率和硬度在固溶6 h达到峰值,之后合金力学性能随固溶时间延长而下降。在固溶处理之后合金在180℃下进行了不同时间的时效处理。随着时效时间延长,Mg2Si相逐渐在基体中析出,析出相显著球化细化,尺寸约为2μm。经过对合金组织和力学性能的分析,半固态挤压铸造A356合金的最佳热处理制度为:540℃固溶6h,180℃时效4h。经过固溶和时效处理后的合金抗拉强度达到336 MPa,延伸率达到6.9%,硬度达到1240 MPa,相较于热处理前的性能提升了106.7%。     

自然时效及预时效6000系合金人工时效析出行为

通过硬度、差示扫描量热法(DSC)及透射电镜分析,研究了自然时效及预时效的几种6000系合金人工时效析出行为.结果表明:在170℃人工时效初期,T4态(固溶淬火后室温放置两周)合金中GP区的溶解过程推迟了β"相的析出,所形成的析出物主要是β"核心,导致时效硬化性下降;而T4P态(固溶淬火后立即170℃人工时效不同时间,然后室温放置两周)合金在这一阶段β"核心连续长大成为β"相,其显微组织以β"析出物为主,导致时效硬化性增强.增加预时效时间,人工时效硬化效果更好.对Si过剩合金,增大Mg/Si质量比,有利于β"核心的析出,提高人工时效硬化性.     

Mg含量对不同热处理的6000系合金成形性及烤漆硬化性的影响

通过硬度、力学性能及成形性试验,研究了Mg含量对不同热处理的6000系铝合金成形性及烤漆硬化性能的影响.结果表明:T4态合金无论是否模拟酸碱洗加热,进行170℃人工时效后,其时效初期的硬度均呈下降趋势,而元素Mg含量的变化影响不大.固溶淬火态和T4P(5min)态合金在模拟烤漆过程中均未出现软化现象.合金的热处理方式对烤漆硬化性的提高比元素Mg的作用更有效.Mg元素的作用主要改变合金的固溶淬火、T4和T4P态的硬度.随Mg含量增加,固溶淬火态硬度单调升高,而T4和T4P态硬度在Mg含量达到1.7%时降低.Mg对T4和T4P(5min)态合金的力学性能和成形性的影响规律是:增加Mg含量,有利于提高合金的强度,但不利于合金的冲压成形.     

半固态挤压铸造A356合金在热处理过程中的组织和性能演化

半固态挤压铸造的A356合金首先在540℃下进行固溶处理,随着固溶温度升高,Mg和Si原子逐渐溶解于基体中,并产生了固溶强化作用。抗拉强度、延伸率和硬度在固溶6 h达到峰值,之后合金力学性能随固溶时间延长而下降。在固溶处理之后合金在180℃下进行了不同时间的时效处理。随着时效时间延长,Mg₂Si相逐渐在基体中析出,析出相显著球化细化,尺寸约为2μm。经过对合金组织和力学性能的分析,半固态挤压铸造A356合金的最佳热处理制度为:540℃固溶6h,180℃时效4h。经过固溶和时效处理后的合金抗拉强度达到336 MPa,延伸率达到6.9%,硬度达到1240 MPa,相较于热处理前的性能提升了106.7%。     

铸造Al8Si0.4Mg合金时效行为研究

利用硬度测定、差热扫描量热分析 (DSC)、电子探针微区成分分析和透射电子显微分析 (TEM)技术研究了铸造Al8Si0 .4Mg合金的铸态时效及固溶淬火时效 (T6)行为。硬度测定结果表明 :Al8Si0 .4Mg合金具有明显的铸态时效硬化效果 ,其铸态时效峰值硬度仅比T6状态硬度值低 6HV。冷却速度对合金时效没有明显的影响。DSC和TEM分析结果表明 :两种时效状态下合金的时效硬化均是过渡相 β″和 β′相析出对基体的强化。对合金在两种时效状态下析出相的分布及硬度均匀化系数进行了分析讨论     

固溶处理对挤压铸造Al17.5Si4Cu0.5Mg0.1Mn合金显微组织及硬度的影响

研究了固溶处理温度和固溶处理时间对挤压铸造Al17.5Si4Cu0.5Mg0.1Mn合金显微组织及硬度的影响。结果表明:固溶处理后合金的显微组织得到明显改善,硬度大幅度提高。随着固溶温度的增加,共晶Si相逐渐粒化,合金的布氏硬度值逐渐增加,当固溶温度为525℃时,共晶Si相形貌相对圆整,合金具有最大布氏硬度值;随着固溶时间的延长,合金显微组织中的共晶Si相发生熔断、粒化、粗化现象,合金的布氏硬度呈现先上升后下降的趋势,当固溶时间为6 h时,合金的布氏硬度达到最大值HB 124。试验得到的挤压铸造Al17.5Si4Cu0.5Mg0.1Mn合金的最佳固溶处理工艺为525℃,保温时间为6 h。     

热处理对Mg-5Sn-1Si合金组织及硬度的影响北大核心CSCD

采用Ar气保护制备了Mg-5Sn-1Si(质量分数,%)合金,并研究了合金的铸态组织和在480℃固溶处理及180℃和280℃不同时效热处理对合金组织中析出相演变的影响及组织与硬度的关系。结果表明,合金铸态组织由α-Mg、共晶Mg2Si、共晶Mg2Sn三相组成;经480℃固溶处理后Mg2Sn相完全固溶,粗大的Mg2Si相得到少量球化;时效处理过程中Mg2Si相得到球化。在180℃时效时,Mg2Sn无沉淀析出,硬度较低,时效保温24 h仅为24.1 HV。在280℃时效时,细小的Mg2Sn相弥散析出并使合金的硬度明显升高,时效保温18 h达到峰值硬度47.6 HV,并随时间的延长出现过时效现象。280℃时效初期,组织中形成较宽的无析出带(PFZ),随着时效时间的延长无析出带PFZ消失。     

固溶-时效对6082合金挤压棒材组织性能的影响

采用力学性能、硬度、电导率测试和电子显微分析技术,研究了固溶-时效处理对6082铝合金挤压棒材组织与性能的影响.结果表明,6082挤压态合金组织除固溶体基体外,还包括微米级的含Cr和Mn的短棒状相、亚微米级的Mg2Si平衡相和α-(AlMnFeSi)夹杂相;固溶过程中亚微米级的Mg2Si平衡相溶解,微米级的含Cr和Mn的短棒状相和α-(AlMnFeSi)夹杂相仍然保留下来,时效过程中过饱和固溶体分解析出主要强化相β"相.合金棒材适宜的固溶一时效制度为545℃×50 min固溶水淬,170℃×8 h时效,在此条件下,合金棒材的抗拉强度、屈服强度和伸长率分别为367 MPa、341 MPa和14.1%.     

RHEOLOGY FEATURE OF SIMPLE METAL MELT

The rheology feature of Sb, Bi melt and alloys was studied using coaxial cylinder high-temperature viscometer. The results showed that the curve of torsion-rotational speed for Sb melt presents a linear relation in all measured temperature ranges, whereas for the Bi melt, the curve presents obvious non-Newtonian feature within the low temperature range and at relative high shear stress. The rheology feature of Sb80Bi20 and Sb20Bi80 alloy melts was well correlated with that of Sb and Bi, respectively. It is considered that the rheology behavior of Sb melt plays a crucial role in Sb80Bi20 alloy and that of Bi melt plays a crucial role in Sb20Bi80 alloy.     

Microstructures and Mechanical Properties of a Newly Developed Austenitic Heat Resistant Steel

The effect of heat treatment on the microstructures and mechanical properties of a newly developed austenitic heat resistant steel(named as T8 alloy) for ultra-supercritical applications have been studied. Results show that the main phases in the alloy after solution treatment are γ and primary MX. Subsequent aging treatment causes the precipitation of M_(23)C_6 carbides along the grain boundaries and a small number of nanoscale MX inside the grains. In addition, with increasing the aging temperature and time, the morphology of M_(23)C_6 carbides changes from semi-continuous chain to continuous network.Compared with a commercial HR3C alloy, T8 alloy has comparable tensile strength, but higher stress rupture strength. The dominant cracking mechanism of the alloy during tensile test at room temperature is transgranular, while at high temperature, intergranular cracking becomes the main cracking mode, which may be caused by the precipitation of continuous M_(23)C_6 carbides along the grain boundaries. Typical intergranular cracking is the dominant cracking mode of the alloy at all stress rupture tests.     

The 15th Global Foundry Sourcing Conference 2014held in Qingdao China

Organized by Suppliers China Co., Ltd and co-organized by the National Technical Committee 54 on Foundry of Standardization Administration of China, the 15th Global Foundry Sourcing Conference 2014 （hereinafter referred to as FSC 2014） was successfully held on Sep. 23rd in Grand Regency Hotel, Qingdao. More than 500 delegates from home and abroad attended this conference, including over 130 purchasers from 20 countries and 380 domestic and foreign suppliers.     

Secondary Recrystallization Behaviors of Grain-Oriented 6.5 wt% Silicon Steel Sheets Produced by Rolling and Nitriding Processes

By rolling and nitriding processes, 0.23- to 0.3-mm-thick grain-oriented 6.5 wt% silicon steel sheets were produced. The core losses of grain-oriented 6.5 wt% silicon steel at frequencies ranging from 400 Hz to 20 k Hz were lower than that of the grain-oriented 3 wt% silicon steel with the same thickness by 16.6–35.8%. The secondary recrystallization behavior was investigated by scanning electron microscopy, energy-dispersive spectroscopy, and electron backscattered diffraction. The results show that the secondary recrystallization in high-silicon steel sheets develops more completely as the nitrogen content increases after nitriding, secondary recrystallized grain sizes become larger, and the sharpness of Goss texture increases. Because more {110}116 grains in the subsurface and the central layer of the sheets have a lot of 20°–45° high-energy boundaries in addition to Goss grains, {110}116 can be the main component through selective growth during secondary recrystallization when the inhibitor quantity is not enough and inhibitor intensity is weaker. The increases in nitrogen content can increase the inhibitor intensity and hinder abnormal growth of a mount of {110}116 grains and therefore enhance the sharpness of Goss texture.     

LASER CLADDED TiCN COATINGS ON THE SURFACE OF TITANIUM

Laser cladded coatings of TiCN were produced on the surface of titanium. To obtain the optimal techniques, several conditions were tested by varying the laser scanning rate. The choice of shielding gas was also studied. The cladded coatings were then evaluated from the surface mechanics point of view based on their microhardness. The microstructure of some interesting samples was investigated by optical micrographs (OM). The results showed that under the condition of fixed pulse frequency and pulse width, the laser scanning rate and the shielding gas are the main factors influencing the components of coatings. TiCN coatings were decompounded and oxidized during the cladding process in the condition of no shielding gas of N2. X-ray diffraction results indicated that the composite coatings composed of TiCN, TiC, Ti2N, and TiO2 were produced using appropriate techniques. The results indicated that the best condition in terms of the surface microhardness is obtained when the scanning rate is 1.5mm / s, the pulse frequency is 15Hz, the pulse width is 3.0ms, and N2 is chosen as the shielding gas. The microhardness of the composite coatings is about 1331kg · mm - 2, which is about 4 times that of the substrate. The optical micrographs indicated that the cladding zone is made up of TiCN, TiO2, and some interdendritic Ti, but the diffusion zone mainly consists of the dendrites phase, and the cladded depth is about 80m, which is more than 2 times that of the laser nitrided sample. There were no microcracks or air bubbles in the cladded sample, which was cladded using the above optimal techniques.     

Microstructure and Mechanical Properties of X80 Pipeline Steel Joints by Friction Stir Welding Under Various Cooling Conditions

X80 pipeline steel plates were friction stir welded(FSW) under air, water, liquid CO_2 + water, and liquid CO_2 cooling conditions, producing defect-free welds. The microstructural evolution and mechanical properties of these FSW joints were studied. Coarse granular bainite was observed in the nugget zone(NZ) under air cooling, and lath bainite and lath martensite increased signifi cantly as the cooling medium temperature reduced. In particular, under the liquid CO_2 cooling condition, a dual phase structure of lath martensite and fi ne ferrite appeared in the NZ. Compared to the case under air cooling, a strong shear texture was identifi ed in the NZs under other rapid cooling conditions, because the partial deformation at elevated temperature was retained through higher cooling rates. Under liquid CO_2 cooling, the highest transverse tensile strength and elongation of the joint reached 92% and 82% of those of the basal metal(BM), respectively, due to the weak tempering softening. A maximum impact energy of up to 93% of that of the BM was obtained in the NZ under liquid CO_2 cooling, which was attributed to the operation of the dual phase of lath martensite and fi ne ferrite.     

INDUSTRY NEWS

China Securities News reported on March 21, 2014： Guangdong Hongtu Wuhan Die Casting Co., Ltd. （Wuhan Hongtu）, a wholly owned subsidiary of Guangdong Hongtu Technology （Holdings） Co., Ltd., held a groundbreaking ceremony recently. With the registered capital of 50 million Yuan, Wuhan Hongtu has a total land area of 100,000 square meters and a plant construction area of 72,000 square meters. It is expected to have a production capacity of about 30,000 tonnes of aluminum castings annually after it is put into production.     

Microstructure,Mechanical Properties and Corrosion Behavior of Extruded Mg–Zn–Ag Alloys with Single-Phase Structure

Mg–Zn–Ag alloys have been extensively studied in recent years for potential biodegradable implants due to their unique mechanical properties,biodegradability and biocompatibility.In the present study,Mg–3Zn-x Ag(wt%,x=0.2,0.5 and0.8)alloys with single-phase crystal structure were prepared by backward extrusion at 340°C.The addition of Ag element into Mg–3Zn slightly influences the ultimate tensile strength and microstructure,but the elongation firstly increases from12%to 19.8%and then decreases from 19.8%to 9.9%with the increment of Ag concentration.The tensile yield strength,ultimate tensile strength and elongation of Mg–3Zn–0.2Ag alloy reach up to 142,234 MPa and 19.8%,respectively,which are the best mechanical performance of Mg–Zn–Ag alloys in the present work.The extruded Mg–3Zn–0.2Ag alloy also possesses the best corrosion behavior with the corresponding corrosion rate of 3.2 mm/year in immersion test,which could be explained by the single-phase and uniformly distributed grain structure,and the fewer twinning.     

GROWTH MORPHOLOGIES OF A BINARY ALLOY WITH LOW ANISOTROPY IN DIRECTIONAL SOLIDIFICATION

Two new classes of growth morphologies, called doublons and seaweed, were simulated using a phase-field method. The evolution of doublon and seaweed morphologies was obtained in directional solidification. The influence of orientation and velocity on the growth morphology was investigated. It was indicated that doublons preferred growing with its crystallographic axis aligned with the heat flow direction. Seaweed, on the other hand, could be obtained by tilting the crystalline axis to 45°. Stable doublons could only exist in a range of velocity regime. Beyond this regime the patterns formed would be unstable. The simulation results agreed with the reported experimental results qualitatively.