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-25Mg(2)Si 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 mu m), 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.