电解铝阳极导杆铝-钢相位摩擦焊工艺及力学性能

传统的电解铝预焙槽阳极导杆采用爆炸焊块作为过渡实现铝导杆与阳极钢爪的连接.针对130 mm×130mm×2 420 mm方铝导杆和端面165 mm×210 mm的铸钢爪,采用相位摩擦焊技术进行焊接,替代原用爆炸块复合焊接的方式,实现自动化生产并达到节能降耗的目的.通过不同工艺参数的试验研究如:摩擦时间、转速、先顶后刹时间、顶锻压力的改变,通过接头力学拉伸试验、冲击试验、显微组织分析得到了最优工艺参数.结果表明,最优工艺方法下可得到致密的焊缝组织以及动态再结晶完善的热影响区组织,接头表现出最优的综合力学性能,满足工业生产要求.     

铝/钢异种金属旋转摩擦焊接研究现状

根据铝/钢异种金属焊接冶金特点及旋转摩擦焊接工艺特点，分析认为旋转摩擦焊最适合铝/钢异种金属轴对称件焊接的工艺。分别介绍了连续驱动摩擦焊和惯性摩擦焊接工艺对铝/钢异种金属焊接接头的组织和性能的影响。总结了铝/钢异种金属摩擦焊接技术研发中亟待解决的主要科学问题，铝/钢旋转摩擦焊过程中摩擦界面及其附近剧烈的塑性流变对IMCs生成的影响规律和机制需要进一步的研究；需要开发相应的工艺措施促进铝/钢接头界面上形成以Fe-Al IMCs为标志的冶金结合，并使IMCs层厚度均匀化。最终指明，研究揭示铝/钢摩擦界面IMCs生成机理、相的组成、形态、分布等冶金行为，对铝/钢旋转摩擦焊接头的组织性能调控具有重要意义，也是铝/钢异种金属焊接结构性能保证的理论基础。     

铝钢复合箱形搅拌摩擦焊焊接结构柱的研究

基于第三届全国大学生焊接创新大赛固定题目焊接结构设计要求,设计一个铝钢复合材料的抗压箱形柱结构,经过有关软件对设计结构进行模拟计算和焊接工艺方法分析,确定了采用搅拌摩擦焊的技术方案。在对实验室近40年的老旧台钻床改造手动搅拌摩擦焊机的基础上进行铝钢丁字接头的搅拌摩擦焊试验。通过实际对铝钢复合结构承受压力测试以及铝钢搅拌摩擦焊焊接接头的界面抗剪强度测试表明,该焊接技术方案满足焊接创新大赛比赛要求,取得很好的比赛成绩。     

LOW TEMPERATURE FRICTION WELDING OF ALUMINUM TO COPPER

经过分析铝-铜摩擦焊接头脆断特点及其原因,在试验的基础上,提出了铝-铜低温摩擦焊工艺。通过降低转速及适当提高摩擦压力,使接头的摩擦加热焊接表面的温度低于铝-铜系统平衡图的共晶点548℃,并保证铝、铜焊接表面金属充分的塑性变形。采用低温摩擦焊消除了铝-铜接头的脆断,提高了接头的强度、塑性、韧性和锻压性能。接头的热稳定性、老化及实际运行试验表明,其质量完全满足技术条件的要求。     

铝—铜低温摩擦焊

经过分析铝-铜摩擦焊接头脆断特点及其原因,在试验的基础上,提出了铝-铜低温摩擦焊工艺。通过降低转速及适当提高摩擦压力,使接头的摩擦加热焊接表面的温度低于铝-铜系统平衡图的共晶点548℃,并保证铝、铜焊接表面金属充分的塑性变形。采用低温摩擦焊消除了铝-铜接头的脆断,提高了接头的强度、塑性、韧性和锻压性能。接头的热稳定性、老化及实际运行试验表明,其质量完全满足技术条件的要求。     

铝/钢异质金属搅拌摩擦焊研究进展

由于铝、钢的热物理性能差异较大,且铁在铝中的固溶度极低,铝/钢异质金属焊接已成为该领域研究的难点与热点。搅拌摩擦焊具有热输入低、热循环时间短等优点,能够有效控制铝/钢接头中金属间化合物的生长,从而获得高质量的焊接接头。文中综述了铝/钢异质金属搅拌摩擦焊国内外研究现状,涉及搅拌头材料选择与结构设计。此外,分析了对接、搭接与点焊三种形式接头的组织与性能,并探讨了铝/钢搅拌摩擦焊技术的未来研究方向。     

防锈铝搅拌摩擦焊接

通过大量试验研究了防锈铝LF21搅拌摩擦焊接技术,深入分析了防锈铝搅拌摩擦焊接头的金相组织和力学性能,并探讨了焊接参数对组织性能的影响.对于3mm厚的防锈铝板,优化的搅拌头材料为ICr18Ni9Ti,形状为圆锥带凹面形,轴肩尺寸为φ12mm,焊针跟部直径为4mm,焊针端部直径为2.8mm,焊针高度为2.7mm.优化的焊接工艺参数范围为旋转速度950-1 500 r/min,焊接速度37.5～60mm/min.研究的成果可应用于有色金属材料搅拌摩擦焊接参数的优化,推动中国搅拌摩擦焊接技术在铝焊接中的应用.     

大截面钢/铝异种金属摩擦焊接工艺研究

采用连续驱动摩擦焊技术对大截面铸态纯铝与Q235钢异种金属进行了焊接工艺试验,通过扫描电镜(SEM)分析接头和断口形貌,测试接头力学性能及其电阻率,得到了纯铝与Q235钢焊接接头的力学性能与焊接参数的关系。结果表明,大截面铸态纯铝与Q235钢间具有良好的摩擦焊接性,焊接界面宏观断口呈均匀银灰色,焊接情况良好,具有100%焊合的特征;采用优化焊接工艺参数施焊的焊接接头力学性能可以达到或超过铝侧基材;接头电阻率介于两侧母材电阻率之间。     

铝/钢异质金属旋转摩擦焊研究进展

铝/钢旋转摩擦焊具有焊接质量好、焊接效率高的突出优势,特别适合轴类、管类结构的焊接制造。但是,由于旋转摩擦焊独特的旋转运动形式导致接头中微观组织与接头性能沿径向分布的不均匀性,成为制约其在关键领域应用的瓶颈之一。文中综述了铝/钢异质金属旋转摩擦焊国内外研究现状,主要分析了旋转摩擦焊工艺、微观组织与力学性能等,并探讨了铝/钢旋转摩擦焊技术未来研究的方向。     

阻碍钢的搅拌摩擦焊研究进展的关键问题

搅拌摩擦焊(FSW)是一种固相焊接技术,在焊接铝、镁及其合金等低熔点金属上发展已相当成熟。焊接异种金属也获得了缺陷少的接头。钢在工业上的应用比其他金属更广泛,因此目前搅拌摩擦焊的研究主要集中在钢板的焊接。本文主要讨论了制约搅拌摩擦焊焊接钢板的3个关键问题,即搅拌头的结构设计、开发价格低廉且有良好高温耐磨性的搅拌头材料及昂贵的搅拌摩擦焊设备。     

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.     

THERMODYNAMICS STUDY ON THE DECOMPOSITION OF CHROMITE WITH KOH

Institute of Process Engineering, Chinese Academy of Sciences, China, has proposed a method for oxidative leaching of chromite with potassium hydroxide. Understanding the mechanism of chromite decomposition, especially in the potassium hydroxide fusion, is important for the optimization of the operating parameters of the oxidative leaching process. A traditional thermodynamic method is proposed and the thermal decomposition and the reaction decomposition during the oxidative leaching of chromite with KOH and oxygen is discussed, which suggests that chromite is mainly destroyed by reactions with KOH and oxygen. Meanwhile, equilibrium of the main reactions of the above process was calculated at different temperatures and oxygen partial pressures. The stable zones of productions, namely, K2CrO4 and Fe2O3, increase with the decrease of temperature, which indicates that higher temperature is not beneficial to thermodynamic reactions. In addition, a comparison of the general alkali methods is carried out, and it is concluded that the KOH leaching process is thermodynamically superior to the conventional chromate production process.