Microstructural and mechanical characteristics of AA1050/mischmetal oxide in-situ hybrid surface nanocomposite by multi-pass friction stir processing

Surface hybrid in-situ aluminum matrix nanocomposite (AMNC) was fabricated by multi-pass friction stir processing (FSP) and a tool traversing speed of 100 mm/min and rotating speed of 1600 rpm with an objective to enhance mechanical properties. Mischmetal oxide (MMO) powder with an initial size of 50 nm, at a concentration of 8.5 vol% was used as the reinforcing particles. EDS particle analyses revealed in-situ solid-state chemical reactions between the Al matrix and the MMO particles. The reaction products, MM3Al and MM3Al11, were distributed uniformly in the discontinuously dynamic recrystallized nano and UFG microstructure. Increasing pass number improved the particle distribution and decreased agglomerated particle size while promoting the in-situ solid-state reaction. The nanocomposite produced by 6 FSP passes enhanced yield stress, 180% (YS = 70 MPa) and strength, 120% (UTS = 132 MPa) while reduced the tensile ductility from 35% to 23%. Fractographic studies showed that dimple-shape ductile fracture mode changed to ductile-brittle mode.