Influence of cryocooling on friction stir processing of Al-5083 alloy

This study is aimed at understanding external cryocooling effects during friction stir processing (FSP) on mechanical and microstructural characteristics of cast solution-treated Al 5083 alloy. An indigenous cooling setup is designed to effectively draw out heat from stir zone during FSP. Microstructural characterization techniques like optical microscopy, EBSD and TEM are employed to ascertain the cooling effect on microstructural evolution. FSP of Al 5083 has resulted in dense distribution of complex precipitates of Mn and Mg depleting the solutes from the matrix grains. Despite the enhancement in strength due to the refinement of grains, there is a huge loss of solid solution strengthening after the FSP. External cooling has major role in the evolution of homogenous fine matrix grains by arresting the grain growth after recrystallization. On the other side, there is no change on precipitate size and its morphology due to external cooling as they form at peak temperatures during FSP and their growth kinetic is fast enough due to availability of deformation energy and thermal energy during FSP. Superior combination of mechanical strength (YS/UTS = 149/316 MPa) and ductility (el.% = 38.4) is achieved for the samples processed with external cryocooling condition. Different strengthening mechanisms involved to the enhancement of yield strength have been analyzed and discussed.