Friction stir welding of a P/M Al-Al2O3 nanocomposite: Microstructure and mechanical properties

Solid-state joining of powder-metallurgy processed (P/M) Al-2 vol% Al2O3 (15 nm) nanocomposite by friction stir welding (FSW) was studied. The nanocomposite was prepared via high-energy mechanical milling followed by hot consolidation processes. The microstructure, mechanical properties and fracture behavior of the welds were evaluated and compared with FSWed wrought 1050 aluminum sheets (WAS). We have found that unlike WAS that can processed at various FSW conditions, the working window for the solid-state joining of P/M nanocomposite is narrow and only feasible at relatively high heating inputs. Microstructural studies showed the formation of melted zones with high hardness at the advancing side of P/M nanocomposite while dynamic recrystallization (DRX) caused grain refinement in WAS specimens with loss of hardness. Consequently, tensile testing revealed higher ultimate strength (UTS) of FSWed P/M nanocomposite (compared to base material) in contrast to WAS welds. Fractographic studies showed that the failure of FSWed P/M nanocomposite was initiated and propagated from the interface of melted zone and thermo-mechanical affected zone (TMAZ) in a catastrophic manner.