The Effect of Friction Stir Processing on Microstructure and Tensile Behavior of Thixomolded AZ91 Magnesium Alloy
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Friction Stir Processing (FSP) to partial sheet thickness can be utilized to engineer unique microstructures in metallic alloys. These composite microstructures consist of three distinct layers associated with stirred, transition and core microstructural regions. The stirred region is of particular interest where severe plastic deformation imparted by the rotating and translating FSP tool under frictional heat leads to grain refinement down to ∼ 1 μm grain size. In this work, partial depth penetration into thixomolded AZ91 Mg plate from the top and bottom surfaces by friction stir processing is explored. Furthermore, low temperature aging treatments are applied to the processed material. The present results with AZ91 Mg show that FSP processed material exhibits higher strength (> 300 MPa), and improvement in ductility (> 7% tensile elongation). It is found that in addition to Hall-Petch strengthening produced by ∼ 1 μm grain size in the stirred region, the enhanced strength levels and ductility are strongly influenced by dispersoids of the intermetallic precipitates found in this alloy.
author list (cited authors)
Mansoor, B., Decker, R. F., Kulkarni, S., LeBeau, S. E., & Khraisheh, M. K.