Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
7972377 | Materials Science and Engineering: A | 2018 | 28 Pages |
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 to develop three kinds of layered microstructured materials. A full thickness fine grained microstructure (FFG), a half thickness fine grained with remaining half in as-cast condition (HFG). The last variation was one third thickness modified into fine grain from both the surfaces and the middle section having as-cast microstructure (SFG). FSP was performed at a tool rotational speed of 720â¯rpm and at a transverse speed of 150â¯mm/min. The coarse α-Mg dendrites with large plate like interconnected β-Mg17Al12 interdendrites were the characteristics microstructure of as-cast AZ91 alloy. Fine grains and uniformly distributed precipitates were the characteristics of FSPed microstructure. High temperature tensile tests were carried out at 350â¯Â°C using three different initial strain rates i.e. 5â¯Ãâ¯10â3 sâ1, 1â¯Ãâ¯10â3 sâ1 and 5â¯Ãâ¯10â4 sâ1. The FFG material showed superplasticity at all strain rates and highest ductility of 680% was achieved at the strain rate of 5â¯Ãâ¯10â4 sâ1. The AC and HFG material displayed very low elongation while SFG material exhibited superplasticity of 388%. The superplastic behaviour in SFG was due to increase in the fraction of fine grained microstructure and modification of as-cast microstructure on both the surfaces. Microstructure and texture studies revealed that grain boundary sliding accommodated by grain boundary migration and grain rotation was responsible for superplasticity in FSPed region.
Related Topics
Physical Sciences and Engineering
Materials Science
Materials Science (General)
Authors
A. Raja, P. Biswas, V. Pancholi,