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Aluminium austenitic stainless steel joints find application in cryogenic engines, spacecrafts and automobiles. This dissimilar material combination is unweldable by conventional fusion welding due to a tendency for brittle intermetallic formation. Solid state welding processes such as friction welding are reported to be employed in such situations. This paper deals with continuous drive friction welding of AA6061 Al alloy to AISI 304 austenitic stainless steel. Direct welding of this combination resulted in brittle joints with 0u bend angle due to the formation of Fe 2 Al 5 . To alleviate this problem welding was carried out by incorporating Cu, Ni and Ag as diffusion barrier interlayers. The interlayer was incorporated by electroplating. Welds with Cu and Ni interlayer were also brittle due to the presence of CuAl 2 and NiAl 3 . Ag acted as an effective diffusion barrier for Fe avoiding the formation of Fe 2 Al 5 . Therefore welds with Ag interlayer were stronger and ductile and could be bent to an angle of 100u.

Various pyrazole‐based P,N (2a–c) and N,N (3a–b) ligands have been synthesized. Using representative ligands, NiII, CoII, CuII, and CuI complexes have been prepared and structurally characterized by crystallography. During complexation of CoII and CuII salts, the phosphane part of the P,N ligand oxidized to phosphane oxide. For N,N donor ligands, a dimeric chloro‐bridged NiII complex was obtained. NiII complex 4 is an active catalyst for ethylene oligomerization. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

The effect of electron beam welding parameters on fusion zone (FZ) microstructure and porosity in a Ti -6.8 Al -3.42 Mo -1.9 Zr -0.21 Si alloy (Russian designation VT 9) has been investigated. It has been observed that the FZ grain width increased continuously with increase in heat input when the base metal was in the ␤ heat-treated condition, while in the ␣ ϩ ␤ heat-treated base metal welds, the FZ grain width increased only after a threshold energy input. The difference is attributed to both the weld thermal cycle and the pinning effect of equiaxed primary alpha on grain growth in the heataffected zone (HAZ) of ␣ ϩ ␤ heat-treated base metal. Postweld heat treatment (PWHT) in the subtransus and supertransus regions did not alter the columnar grain morphology in the FZ, possibly due to the lack of enough driving force for the formation of new grains by the breaking up of the columnar grains and grain boundary movement for grain growth. As the PWHTs were conducted in a furnace, the role of thermal gradients can be ruled out. Intragranular microstructure in the aswelded condition consisted of hexagonal martensite. The scale of the martensite laths depended on welding speed. The highest porosity was observed at intermediate welding speeds. At low speeds, a majority of pores formed at the fusion boundary, while at high speeds, occurrence of porosity was maximum at the weld center. The trends on porosity can be explained on the basis of solubility of hydrogen in titanium as a function of temperature and the influence of weld thermal cycle on nucleation, growth, and escape of hydrogen gas bubbles. The porosity at slow welding speeds is low because sufficient time exists for the nucleation, growth, and escape of hydrogen gas bubbles, while insufficient time exists for the nucleation of gas bubbles at high welding speeds. The effect of pickling of joint surface, vacuum annealing of the base metal, and successive remelting of the weld metal has also been investigated.

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