枝晶α在Al-Si铸造合金中的作用

简要介绍了铸造Al-Si合金中枝晶α数量与合金力学性能之间的关系，以及增加枝晶α数量和改善其组织形态的途径，认为增加枝晶α数量为进一步提高合金的力学性能提供了可能。     

高性能低成本铸造近共晶Al-Si-Mg合金

考察了Sr、Sr B对近共晶Al-11.6%Si-0.4%Mg合金组织与力学性能的影响,并测定了T6状态下枝晶α相的显微硬度.Sr变质处理可增加组织中枝晶α相的数量,初晶α相呈细长的高度分枝的柱状枝晶,可显著改善合金的力学性能,特别是塑韧性.T6状态下,枝晶α相的显微硬度先随Sr量的增加而增加,在0.025%Sr处达到峰值,随后下降.在Sr变质的合金中加入B,细长的柱状枝晶转变成等轴枝晶;随着合金中B量增多,枝晶团尺寸显著减小,T6状态下枝晶α相的显微硬度增加.对于近共晶Al-Si-Mg合金,Sr变质 B细化联合熔体处理是非常必要的,可同时显著提高合金的抗拉强度和伸长率.     

Sr对近共晶Al-Si合金中α枝晶生长行为的影响

针对Al-11.6%Si和Al-11.6%Si-0.4%Mg两种近共晶成分铸造合金。考察了Sr的加入对组织中α枝晶形态的影响，测量了完全变质合金中α枝晶相数量及α枝晶的特征参数；一次分枝间距和二次枝臂间距。结果表明，Sr的加入促进了α枝晶柱状化生长并导致α枝晶相数量大幅度提高；在完全变质合金中，随着合金中Sr量增加。一次分枝间距和二次枝臂间距都降低。Sr对α枝晶起一定的细化作用。Sr加入到Al-Si合金中引起合金液的性质发季了显著变化。Sr的存在降低了α枝晶固液界面能。导致枝晶尖端的生长过冷度降低。抑制液相中等轴晶的形核，因此Sr的加入促进了柱状枝晶的形成。固液界面能的降低也使得柱状枝晶的二次枝臂间距和一次分枝间距随着Sr量增多而降低。     

变质和热处理对A354缸盖组织和性能的影响

对不同锶含量的A354合金缸盖热处理冷却曲线、硬度、力学性能及组织检测。结果表明,锶变质增大了合金熔体过冷度,促进了共晶硅片状向蠕虫状转变,并有利于铝枝晶的细化;固溶促进共晶硅片状向粒状转变。A354铸造合金缸盖变质最佳锶量为0.14%~0.18%,锶含量过高铝合金力学性能降低。     

Ba变质对亚共晶Al—Si合金初生α固溶性的细化作用

用含钡中间合金处理亚共晶Ａｌ－Ｓｉ合金，重点研究了Ｂａ元素细化α固溶体的效果和机理。研究表明：当合金中残留含Ｂａ量为０．０５％－０．０８％时，无论是硅晶体还是α固溶体均获得了最佳的变质和细化效果，力学性能也出现了峰值效应。扫描电镜和电子探针结果表明：Ｂａ元素主要吸附在α固溶体的枝晶间和枝晶前沿，因阻碍α固溶体的过快生长和促进枝晶分枝，熔断等耐起到了细化作用。     

锶变质近共晶Al-Si合金力学性能与枝晶α-Al特征参数的相关性

测量了用不同Sr加入量变质的近共晶Al Si合金中枝晶α Al的一次分枝间距和二次枝晶臂间距 ,考察了枝晶α Al特征参数的变化对合金力学性能的影响。研究结果表明 :Sr的加入可以细化枝晶 ,表现为一次分枝间距和二次枝晶臂间距随合金中Sr含量的增加而减小 ;枝晶细化可以提高合金的力学性能 ,合金的铸态力学性能与枝晶α Al的特征参数是高度线性相关的     

高锌Al-Zn-Cu合金中Zn的存在形式及其对力学性能的影响

采用熔铸法制备了Zn含量分别为12wt%、14wt%、16wt%和18wt%的4种高锌Al-Zn-Cu合金,并对合金的显微组织、相组成和力学性能进行了详细分析,重点探讨了合金中Zn的存在形式及其对力学性能的影响。结果表明,4种不同锌含量的合金均由花瓣状的α-Al枝晶和晶界相Al2Cu组成,尽管Zn含量的增加导致晶界Al2Cu相的数量增加以及α-Al枝晶的细化,但Zn主要以固溶形式存在于固溶体相α-Al中。Zn含量的增加显著提高Al-Zn-Cu合金的强度而明显降低塑性的主要原因可归于Zn对α-Al固溶体的固溶强化效应。Al-Zn-Cu合金的断裂由韧窝状断裂向解理断裂转变。     

Ba 变质对亚共晶 Al-Si 合金初生α固溶体的细化作用

用含钡中间合金处理亚共晶Ａｌ－Ｓｉ合金,重点研究Ｂａ元素细化α固溶体的效果和机理。研究表明：当合金中残留含Ｂａ量为０．０５％～０．０８％时,无论是硅晶体还是α固溶体均获得了最佳的变质和细化效果,力学性能也出现了峰值效应。扫描电镜和电子探针结果表明：Ｂａ元素主要吸附在α固溶体的枝晶间和枝晶前沿,因阻碍α固溶体的过快生长和促进枝晶分枝、熔断等而起到了细化作用。     

钠,锶变质铝硅合金机理的研究

通过对工业用铝硅类合金中硅相在变质前后形态的金相和扫描电镜观察,结合近年来国内学者的有关研究结果,对钠和锶的变质行为进行了分析,认力共晶硅的变质主要是由于孪晶分枝生长和共晶α相封锁硅枝晶的侧面生长所致。     

A356铝合金中裂纹的萌生及其扩展

研究了A356铝合金在冲击载荷作用下的裂纹萌生及其扩展过程。结果表明：α-Al枝晶二次枝晶臂间板片状共晶体是材料中最薄弱的区域。该区域中尺寸最大的Si颗粒首先发生断裂形成裂纹源，而枝晶与枝晶间体积较大的块状共晶体强度相对较高，裂纹源不会首先在该区域;正确性同裂纹优先在板片状共晶体中传播，而块状共晶体对裂纹的传播有一定阻碍作用，要提高合金的力学性能就必须设法减少或消除薄弱的板片状共晶体的相对数量。建立了A356合金在啊大；和作用理生、长大及传播的模型，用这个模型解释了提高冷却速度以获得细晶粒的方法并不一定能提高合金的抗拉强度；相反，使用高效的晶粒细化剂能够减少或消除板片状共晶体，从而可能会提高合金的性能。     

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 80?滋m, 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.