Enhancing the mechanical and tribological properties of Mg2Si-rich aluminum alloys by multi-pass friction stir processing

Particle strengthening of in-situ Al-Mg2Si composites hinges on effective geometrical parameters (size, distribution, morphology, and volume fraction) of the inherent primary Mg2Si particles. The use of solid-state friction stir processing (FSP) in a multi-pass mode is recognized as a secondary processing route capable of achieving desirable geometrical parameters of Mg2Si particles in Al-Mg2Si composites as compared to other routes. This paper thus studies the microstructure, mechanical properties, and tribological behavior of the multi-pass FSPed in-situ Al-25Mg2Si composite with a threaded triangular pin tool. The FSP was conducted at constant tool rotational and traverse speeds of 1000 rpm and 80 mm/min for 1–6 passes. The results showed a decline in the average Mg2Si size (115–3.25 μm), porosity content (5.8–0.14%), and primary Mg2Si particle-depleted region as the FSP passes are increased (0–6). Improved geometrical parameters of the primary Mg2Si particles enhance microhardness (178–272 HV), tensile strength (102–233 MPa) and wear resistance of the Al-25%Mg2Si composite via particle dispersion and dislocation strengthening effects, grain refinement, and microstructural densification. Multi-pass FSP can be adopted as a better substitute to element addition, casting modification, heat treatment and electromagnetic stirring in effectively controlling the geometrical parameters of the primary Mg2Si in in-situ Al-Mg2Si composites for improved mechanical and tribological properties. © 2020 Elsevier B.V.