T ype 5052 aluminium alloy was joined to type 304 austenitic stainless steel via a continuous drive friction welding process. T he joint strength increased, and then decreased after reaching a maximum value, with increasing friction time. Joint strength depended on the size and shape of the tensile testpiece. Friction weldability could be estimated by electrical resistmetry. T he process of friction welding between the aluminium alloy and the stainless steel is proposed to evolve as follows: welding progresses f rom the outer to the inner region; an unbonded region is retained at the centre of the weld interface with shorter friction time; longer friction time causes the formation of an intermetallic reaction layer at the weld interface; and the reaction layer grows as the f riction time increases. W hen the thickness of the reaction layer increased above a critical value, the joint was brittle and fractured at the weld interface. T he joint was sound when there was no unbonded region and a thin reaction layer formed along the entire weld interface.MST /4250

No abstract

Friction welding was carried out between TiNi alloy and austenitic stainless steel with and without a Ni interlayer. When TiNi alloy was welded to stainless steel without the Ni interlayer, a large amount of brittle Fe 2 Ti intermetallic compound was formed at the weld interface. The formation of this brittle compound led to degradation of the joint strength. The Ni interlayer changed the microstructures at the weld interface and improved the joint strength. A fracture occurred at the interface between Ni and TiNi. The interface between Ni and TiNi was free from Fe 2 Ti and consisted of mainly TiNi 3 and TiNi. After TiNi 3 was formed as the reaction layer, a eutectic reaction occurred between the TiNi 3 and TiNi base alloy. A reaction layer with a eutectic structure tends to form at the periphery, where the temperature would be higher than that of the central region.

A type 1050 commercial aluminium was bonded to a type 304 austenitic stainless steel using a continuous drive friction welding process. The bonding interface conditions were evaluated by means of mechanical tests, to measure tensile and bending properties, and ultrasound microscopic observation. The tensile strength of the joints increased as the frictional time increased. High strength joints could be obtained at africtional time greater than 0·2 s. However, ultrasound microscopy clearly showed that bonding progress occurred from the peripheral region towards the centre of the faying surface and, furthermore, that the frictional time of 0·2 s was not sufficient for complete bonding and much more frictional time was necessary. It is thus difficult to exactly evaluate the joint strength of a soft-hard metal combination by tensile and bending tests alone. Therefore, ultrasound microscopic observation together with mechanical testing is recommended as a convenient method to evaluate such a joint.MST/3565

The microstructures of commercial purity aluminium near the friction weld interface were observed by transmission electron microscopy. Large plastic deformation of aluminium occurred near the weld interface and the microstructure of the aluminium was oriented from the centre to the periphery of the weld nugget. The aluminium grains were re® ned, and there were many recrystallised grains which were almost dislocation free. The re® ned grains, which were of size ~1 m m, formed very near the weld interface. The grain boundary was estimated to be a large angle tilt boundary. The re® ned grains were mainly formed by dynamic recrystallisation during the upset stage of the welding cycle. A large amount of shear strain and heat were introduced during the friction stage, and dynamic recrystallisation started during the upset stage. Grain growth occurred during air cooling after the upset stage. The grain size was larger in the central region than in the periphery owing to the variation in temperature. The Vickers microhardness of aluminium near the weld interface increased owing to the microstructural re® nement.MST/4831