Elucidation of the factors controlling interface decohesion and particle fracture in a friction stir alloyed Al‒Fe alloy system

Abstract

In the present study, an Al‒Fe alloy was fabricated by the solid-state friction stir alloying (FSA) technique. The FSA was carried out at a constant linear speed and variable tool rotational speed ranging from 600 to 1200 RPM. The ultimate tensile strength (UTS) and total elongation (TE) of the alloy fabricated at lower tool rotational speeds (600 and 900 RPM) are ∼ 300 MPa and ∼ 10%, respectively. Whereas the UTS and TE of the alloy fabricated at higher tool rotational speeds (1200 and 1500 RPM) are ∼ 110 MPa and ∼ 20%, respectively. The transition in the fracture behavior of the alloy from brittle to ductile was observed at a tool rotational speed of 900 RPM. The brittle fracture of alloys fabricated at low tool rotational speeds is primarily associated with Al/Fe interface decohesion and coarse Fe particle fracture. Whereas the void growth and coalescence are responsible for ductile fracture in alloys fabricated at higher tool rotational speeds. The transition of the dominant strengthening mechanism from dislocation and precipitation strengthening in alloys fabricated at lower tool rotational speeds to Hall‒Petch strengthening in alloys fabricated at high rotational speeds is the primary reason for the drastic change in the fracture behavior of these alloys. The coarse undissolved Fe particles and finely dispersed Al13Fe4 contributed significantly to kinematic and isotropic work hardening, which resulted in an extremely high work hardening rate in the alloys fabricated at lower tool rotational speeds.