Microstructure evolution, mechanical properties and corrosion resistance of biological particles reinforced AZ31 magnesium matrix composites fabricated by high rotating speed friction stir processing

Abstract

Friction stir processing (FSP) with high rotating speed were successfully employed to fabricate a novel AZ31 magnesium matrix composites (MMCs) reinforced by biological particles of nano-hydroxyapatite (nHA) and nano-magnesium oxide (nMgO). The influences of tool rotating speed on the microstructure evolution, mechanical properties and corrosion resistance of MMCs were investigated. In results, high rotating speed not only significantly refined the grains of the stirred zone (SZ) in MMCs due to sufficient dynamic recrystallization (DRX), but also reduced the size of β-Al12Mg17 precipitates and caused them homogeneously distributed. With the increase of rotating speed, the bio-reinforced particles exhibited a larger range with uniform distribution in SZ of MMCs, and the microhardness, tensile strength and corrosion resistance of MMCs were also improved. At high rotating speed of 6000 rpm, MMCs had a maximum tensile strength of 235.5 MPa with cleavage fracture of ductile-brittle mixed mode. Meanwhile, the self-corrosion potential of MMCs (−1.408 V) was 10.4% higher than the matrix (−1.571 V), while the self-corrosion current density (9.328 × 10−5 A/cm2) was 96.4% much lower than the matrix (2.607 × 10−3 A/cm2), indicating that the corrosion resistance of MMCs was significantly enhanced than matrix. And the corrosion morphologies of MMCs presented mud cracking due to relatively uniform corrosion.