A pathway towards strengthening and ductilization of additive-manufactured AlSi10Mg through friction stir processing: Microstructural evolution and tensile behavior

A systematic investigation was undertaken to elucidate the strengthening and ductilization mechanisms in laser powder bed fusion (LPBF) AlSi10Mg post-treated by low-to-high rotational speed friction stir processing (FSP). FSP led to a significant enhancement in tensile fracture strain, rising from 0.04 to 0.21, attributed to the elimination of LPBF porosities, microstructural inhomogeneity, and fragmentation of the Si network. However, under identical conditions, it resulted in a decrease in yield strength from 337 MPa to 206 MPa. Continuous and geometrically dynamic recrystallization during FSP governed the grain structure formation. The average grain size was almost constant (between 2.1 and 2.6 μm) owing to the Zener pinning effect of the Si particles. A model proposed to predict the yield strength indicated that the load bearing of the Si particles was the dominant strengthening mechanism. In addition, another model for examining the ductilization mechanism indicated that the initiation and propagation of voids and cracks are delayed to higher strain values at higher rotational speeds. The origins of the strengthening and ductilization mechanisms are discussed in detail.