(Session 7B)Microstructures and mechanical properties of friction stir welded joints of Zr-Ti alloy

摘要

Zr-Ti alloy joints were successfully produced by methods of friction stir welding. Unlike the (a+p) dual-phase microstructure in base metal, there existed only β phases in the portion of heat affected zone, the whole of thermo-mechanical affected zone and nugget zone of the as-welded joint due to higher welding heat and faster cooling rate. Accordingly, the hardness in these regions exhibited integral decrement and uniform distribution feature. The thermal simulation further proved that the hardness variation was mainly determined by the phase composition. A satisfactory ultimate tensile strength and elongation equal to the base metal were obtained for the as-welded joint. The tensile fracture occurred at the heat affecting zone near to the retreating side of the joint. The fracture surface of the joint exhibited mixing feature with quasi-cleavage facets and small dimples.