Effect of layered microstructure on the superplasticity of friction stir processed AZ91 magnesium alloy

摘要: Abstract Multipass friction stir processing (FSP) was performed in as-cast AZ91 Mg alloy (AC) to generate layered microstructure through the thickness and study its effect on superplasticity. The FSP tools with different tool pin length were used develop three kinds of microstructured materials. A full fine grained (FFG), a half remaining condition (HFG). last variation one third modified into grain from both surfaces middle section having (SFG). at rotational speed 720 rpm transverse 150 mm/min. coarse α-Mg dendrites large plate like interconnected β-Mg17Al12 interdendrites characteristics alloy. Fine grains uniformly distributed precipitates FSPed microstructure. High temperature tensile tests carried out 350 °C using initial strain rates i.e. 5 × 10−3 s−1, 1 × 10−3 s−1 5 × 10−4 s−1. FFG material showed superplasticity all highest ductility 680% achieved rate AC HFG displayed very low elongation while SFG exhibited 388%. superplastic behaviour due increase fraction modification surfaces. Microstructure texture studies revealed that boundary sliding accommodated by migration rotation responsible for region.