of the original manuscript:Vaidya, W.V.; Horstmann, M.; Ventzke, V.; Petrovski, B.; Kocak, M.; Kocik, R.; Tempus, G.:
AbstractDissimilar welds of aluminium alloy AA6056 and titanium alloy Ti6Al4V were produced by a novel technique. AA6056 sheet was machined at one end to a U-slot shape, enabling the intake of the Ti6Al4V sheet. The Al-alloy U-slot was then butt welded by split laser beam without using a filling wire, thus making a weld by melting only the Al-alloy.Thereby the intermetallic brittle phase TiAl 3 formed at the weld interface and affected mechanical properties. As a continuation of the previous work, the joint design was modified by chamfering Ti6Al4V to reduce the formation of interfacial TiAl 3 . It is shown in this work how this seemingly insignificant joint modification has refined microstructure and increased hardness and strength. The most impressive feature was the improved resistance to fatigue crack propagation whereby the fracture type in the fusion zone of AA6056 adjacent to the weld interface changed from partially intercrystalline to completely transcrystalline. Possible metallurgical processes leading to the property improvements are discussed.
Alternating nanometric layers of titanium and aluminium were used as filler material to promote joining between titanium aluminide samples. The improved diffusivity of these nanometric layers is thought to overcome the difficulties in solid-state joining of titanium aluminides without producing chemical discontinuities at the interface. In this study, a thin multilayer (alternating titanium and aluminium layers), 2 mm thick, was deposited by dc-magnetron sputtering onto the two surfaces to be joined. The effects of processing conditions and the thickness of nanometric layers on microstructure and chemical composition variation across the interface have been analyzed. Sound regions can be obtained at temperatures as low as 600 C but higher temperatures (800e1000 C) are needed to obtain completely sound joints. During processing, the asdeposited film evolves to a nanocrystalline TiAl layer which may explain why the bond region is slightly harder than the base material.
a b s t r a c tExperimental and numerical studies were conducted to characterize laser and resistance spot welds to gain an understanding of load carrying capacity, temperature distributions and residual stress states of different joint geometries used in the automotive industry. Different laser spot weld path geometries are compared with conventional resistance spot welds to find the residual stress distributions in each. It was found out that the weld region in laser spot welding is surrounded by a compressive region which has higher compressive stress values and larger size than that of resistance spot welds. Simulations showed good agreement with experimental temperature distributions, and were able to qualitatively predict the residual stress distributions in each of the weld geometries. The thermal history at known failure locations within the welds and the influence of the weld geometries on cooling rate are also discussed.
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