固液混合铸造Al-40Si合金的显微组织和力学性能

采用固液混合铸造的Al-40Si合金组织细小，合金力学性能明显优于传统铸造和半固态加工合金，并且解决了传统铸造Al-40Si合金铸件难以热加工的问题。在本工艺条件下，当添加平均粒度为120μm的粉末且粉末添加量与合金熔体质量比为1时，Al-40Si合金中的初晶硅平均粒度可控制在30μm以下；材料的室温力学性能为：σb=119.6MPa，σ0．2=105MPa，δ=1．43％。     

结晶过程中合金粉末的加入对Al-Cu合金凝固组织的影响

在固液混合铸造工艺中,将Al-20Cu合金粉末分别加入到Al-20Cu和Al-40Cu合金熔体中制备了合金坯料。采用JSM-6700F扫描电子显微镜对合金坯料的显微组织进行观测。研究结果表明:Al-20Cu粉末加入对粉末周围的Al-20Cu合金基体初生相、共晶组织和二次析出相有明显的细化作用,越靠近未熔粉末,基体中的初生相越细小,共晶组织的片间距越小。固液混合铸造Al-40Cu合金坯料中未熔Al-20Cu合金粉末与基体界面结合良好,表明固液混合铸造工艺中加入的金属粉末的成分范围可以进行扩展。     

Al-8.7Fe-1.6V-1.3Si耐热铝合金的固液混合铸造

研究了耐热铝合金Al-8.7Fe-1.6V-1.3Si（8009）的固液混合铸造。结果表明：采用固液混合铸造工艺制备的耐热铝合金显微组织明显细化，室温和高温力学性能明显优于铸造和搅拌铸造耐热铝合金。固液混合铸造坯具有良好的挤压性能，挤压坯具有优异的室温和高温耐磨性能。在本工艺条件下，当粉末添加质量和合金熔体质量比为1时，耐热铝合金中的Al13Fe4析出相粒径可控制在30μm以下，材料的室温力学性能为：σb＝210MPa，σ0．2＝190MPa，δ＝4％；在473K时为：σb＝150MPa，σ0．2＝130MPa，δ＝5％；在573K时为：σb＝110MPa，σ0．2＝90MPa，δ＝6％。     

固液混合铸造技术

固液混合铸造是在过热的合金熔体中加入大量的同种成分或润湿性好的异种合金粉末,在保护气氛中强烈搅拌至半固态然后压铸成形或进行其他热加工的一种新型的材料制备技术.本文结合作者在固液混合铸造Al-Mn、Al-Cr合金等方面的研究工作,综合介绍了固液混合铸造技术的研究状况.当前研究表明:固液混合铸造技术能有效细化合金晶粒,提高材料的力学性能,有一定的研究和应用价值.     

固液混合铸造高铬铸铁的热变形性能研究

采用一种新的材料制备技术-固液混合铸造工艺制备了高铬铸铁合金坯料,对合金进行了高温热压试验,并对热压过程和合金组织进行了观察和分析。研究结果表明,固液混合铸造的高铬铸铁合金相对于普通铸造合金的热变形性能得到明显提高,累计墩粗变形比可达到34%以上,固液混合铸造工艺对高铬铸铁合金组织的改善是提高材料热变形性能的主要原因。     

固液混合铸造制备高合金锭坯的工艺研究

采用固液混合铸造制备了Al-10Mn和Al-10Cr合金坯料,研究了制备工艺及其对材料组织及性能的影响.采用先加入一定的粉末,搅拌后再分多次加入剩余粉末的加粉方式.当合金熔体的过热度为10～40℃、搅拌器转速为500r/min,压铸模温度为500～600℃时,能够获得组织均匀、细小的固液混合铸造合金.随着加粉量的增加和粉末粒度的减小,铸造坯料的力学性能也随之升高,这两种新合金可以应用于耐磨、耐蚀材料.     

Cr15高铬铸铁固液混合铸造铸件组织的研究

利用固液混合铸造制备了Cr15高铬铸铁,并利用光镜和扫描电镜对合金的微观组织进行了研究。结果表明,与普通铸造相比,固液混合铸造制备的Cr15高铬铸铁共晶碳化物被细化、球化,奥氏体为细小的等轴晶,共晶团尺寸显著减小,粒度为20￣50μm。     

固液混合铸造ZA60合金微观组织的研究

采用固液混合铸造技术制备了ZA60舍金，并与传统金属型铸造、半固态铸造对比，研究ZA60合金的组织变化规律及粉末加入量对固液混合铸造工艺ZA60合金组织的影响。结果表明，在合金熔体过热度为40℃，加入粉末粒度为200～400目时，加入40％的粉末量对ZA60合金有明显的组织细化作用；相对于金属型铸造和半固态铸造，固液混合铸造ZA60合金组织明显细化、球化，且组织比较均匀。固液混合铸造时组织改变的原因主要与搅拌作用和加入合金粉末时的激冷作用、形核作用有关；固液混合铸造时试样中β相和η相数量较少，主要与冷却速度相对较快有关。     

铝质轻合金固液混合铸造的研究

固液混合铸造是一种新型的材料制备技术.结合固液混合铸造Al-Mn、Al-Cr、Al-Cu等合金的具体研究工作,综合介绍了固液混合铸造技术的研究状况.当前研究表明,固液混合铸造技术能有效细化合金晶粒,提高材料的力学性能,且工艺简单、生产成本低廉、能成形复杂形状件和大件,具有一定的研究和应用价值.     

不同Mn含量的Al-Mn合金的研究

采用固液混合铸造研究了Al-10Mn、Al-15Mn和Al-20Mn合金的显微组织和力学性能.研究表明:固液混合铸造能有效地细化Al-Mn合金组织,其初生相尺寸可控制在10 μm以内,且形貌以球形或等轴状为主;合金的抗拉强度大大提高,由传统铸造的40～60 MPa提高到110～160 MPa,伸长率由零提高到1%左右;传统铸造和固液混合铸造的Al-Mn高合金的组织随着Mn含量的增加而更加粗大,抗拉强度则下降,硬度有所提高.采用固液混合铸造这一新型的材料制备技术,可以扩展Al-Mn等高合金材料的研究和应用的成分范围.     

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.     

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.     

STUDY ON PROPERTIES OF PULSE ELECTRODEPOSITED RE-Ni-W-P-SiC COMPOSITE COATINGS

The effects of pulse frequency f and duty cycle r on the deposition rate, composition, morphology, and hardness of pulse electrodeposited RE （rare earth）-Ni-W-P-SiC composite coatings have been studied. The results indicate that pulse current can improve the deposition rate of RE-Ni-W-P-SiC composite coatings; W, P, and SiC contents in the coating decrease with the increase of pulse frequency and reach the lowest value at f = 33Hz, whereas the RE content in the composite coatings increases with the increase of pulse frequency. SiC content decreases with the increase of duty cycle, W content reaches the lowest value, and P content reaches the highest value at r = 0.4; pulse current and RE can lead to smaller size of the crystalline grains; however, the effects of different pulse frequency and duty cycle on the morphologies of RE-Ni-W-P-SiC composite coatings are not obvious. The hardness of RE-Ni-W-P-SiC composite coatings is the highest when the duty cycle is at 0.6 and 0.8 and pulse frequency is at 50Hz. At the same pulse frequency, the hardness of RE-Ni-W-P-SiC composite coatings at r= 0.8 is higher than that at r= 0.6.     

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.     

RELATIONSHIP BETWEEN J-INTEGRAL AND FRACTURE SURFACE AVERAGE PROFILE

To investigate the causes that led to the formation of cracks in materials, a novel method that only considered the fracture surfaces for determining the fracture toughness parameters of J-integral for plain strain was proposed The principle of the fracture-surface topography analysis （FRASTA） was used. In FRASTA, the fracture surfaces were scanned by laser microscope and the elevation data was recorded for analysis. The relationship between J-integral and fracture surface average profile for plain strain was deduced. It was also verified that the J-integral determined by the novel method and by the compliance method matches each other well.