Investigation of microstructure and corrosion behavior of AZ91/64SiO2-31CaO-5P2O5 composite wire fabricated by friction stir back extrusion

In this study, the AZ91-bioactive glass surface composite wires were created using a unique method called friction stir back extrusion (FSBE). The microstructure, mechanical properties, and corrosion resistance of FSBE-processed wires were studied. The results show that by applying the FSBE process, the amount of β-Mg17Al12 phase decreased compared to the as-cast AZ91 rod. Also, by increasing rotational speed during FSBE, the distribution of bioactive glass powder in the AZ91 matrix become more homogenous, and gradient AZ91 matrix composite is fabricated at a rotational speed of 1200 rev/min. By increasing temperature and plastic strain during FSBE at high rotational speed, the higher amount of discontinuous β-Mg17Al12 phase and α + β eutectic formed in the grain boundaries. By inserting bioactive glass powder using a hole drilling method and applying the FSBE process, a gradient AZ91-bioactive glass composite wire with ultimate tensile strength, yield strength, elongation, and corrosion resistance of 58, 64, 62, and 34 % higher than AZ91 as-cat rod can be achieved. Also, the corrosion resistance of gradient AZ91 matrix composite at simulated body fluid (SBF) increased 48 % compared to as-cast AZ91 base metal.