Microstructure and Impression Creep Behavior of Al Based Surface Composite Produced by Friction Stir Processing

Abstract

Al Fe surface composites were prepared through friction stir processing route by using commercial pure aluminium sheet and iron powder. Friction stir processing was done with a tool made up of high speed steel having a 3 mm pin at the tip. Microstructural features of the friction stir nuggets were characterized by using X-ray diffractometry, scanning electron microscopy, energy dispersive spectroscopy and transmission electron microscopy. Creep behaviour of the friction stir zone was studied using impression creep techniques. Impression creep experiments were done on substrate aluminium and friction stir region. The results show that the surface of Al substrate is converted into a composite, consisting of Al, Fe powders and iron aluminides. The aluminium grain size is drastically reduced, with a large fraction of crystallites having size in the range of 70 nm. Fe particle size was reduced drastically resulting in interparticle spacing in the range of 500 nm. Dislocation density was drastically increased. Impression creep experiments indicated that friction stirred region shows marginally lower activation energy compared to the base metal. This is attributed to the metastability in the structure in the form of extremely fine grain size and high dislocation density. Because of the combined effect, creep in stir zone takes place with a smaller activation energy compared to creep in base aluminium. 2016, The Indian Institute of Metals - IIM.