Influence of tool rotational speed on microstructural characteristics of dissimilar Mg alloys during friction stir welding

Dissimilar friction stir welding of the AZ80A Mg alloy as the advancing side and the AZ91C Mg alloy as the retreating side was carried out at a constant feed rate of 75 mm/min using a taper cylindrical pin profiled tool at different tool rotational speeds. Defect free welds were produced in the 700-900 rpm rotational speed range. During friction stir welding, extrusion of metal took place in the advancing side and this extruded material was dynamically recrystallized and redeposited on the retreating side. This experimental investigation revealed that friction stir welding leads to the formation of comparatively finer sized grains on the retreating side of the thermo-mechanically affected zone compared to grains in the thermo-mechanically affected zone on the advancing side. Moreover, the heat affected zone of AZ80A possessed fine sized grains compared to the heat affected zone of AZ91C. Additionally, increasing tool rotational speed influenced the tensile strength of the fabricated joints.