Formation of thermo-mechanically affected zone in friction stir welding

Abstract

The thermo-mechanically affected zone (TMAZ) is an exclusive zone formed in friction welded joints as a transition zone between the stir zone (SZ) and the heat affected zone (HAZ). This zone is crucial from the mechanical and microstructural aspects. In this work, the formation of TMAZ and its morphology in different friction stir welded and processed materials are investigated. The base materials taken to consideration are copper, aluminum and magnesium alloys. The results show that, the formation of this zone is severely depended on the base material type. In the AZ91 magnesium alloy due to presence of hard intermetallic precipitations (β phase) around the grain boundaries, the TMAZ emerges as an evident zone with deformed grains in a special direction. In the 5083 aluminum alloy, TMAZ in not as clear as what emerged in AZ91 magnesium alloy but, can be find a bit hardly with some misaligned microstructural texture. On the other hand, in the pure copper, due to not presence of any hard phase/precipitates or specific dominant alloying element, the TMAZ does not form. Actually in this type of materials, the deformed grains supposedly located in TMAZ are recrystallized and found a microstructure similar to SZ or base material.