Microstructure evolution and microhardness of friction stir welded cast aluminum bronze

Abstract

Microstructural characteristics and mechanical properties of a friction stir welded cast aluminum bronze (Cu–9Al–1Fe), produced by a sand casting method, have been investigated at tool rotation of 850–1500rpm and traverse speed of 50–100mm/min. Refinement of the primary coarse cast microstructure in the base metal was seen after friction stir welding. Microstructure of the stir zone was characterized in four distinct areas of non-isometric fine grains while a significant grain growth was noticed in some of the areas. Conditions of grain growth are defined with high heat input intensity and low heat transfer capability. The grain size was observed to decrease after FSW, resulting in a greater microhardness across the welded region from about 100 HV in the base metal to about 150 HV at the center of the stir zone. The increased hardness in the stir zone may have stemmed from the locally refined grain size according to Hall–Petch relation.