Fabrication of new gradient AZ91-bioactive glass composite using friction stir back extrusion

This study investigated the microstructure, mechanical characteristics, and in vitro corrosion behavior of gradient AZ91-bioactive glass composite wire fabricated by friction stir back extrusion. The results showed that by decreasing the extrusion speed from 40 to 20 mm/min, the distribution factor of bioactive glass increased from 0.31 & PLUSMN; 0.04-0.45 & PLUSMN; 0.07, and more homogenous grain size was formed at the surface and center zone of the composite wire. Under the influence of heat and plastic deformation during friction stir back extrusion, despite the formation of the & beta;-phase in separate islands, the & alpha; + & beta; eutectic phase was also formed in the com-posite wire. In composite wire processed with a rotational speed of 800 rpm and extrusion speed of 20 mm/min, a gradient distribution of bioactive glass was formed in the cross section of the wire. Compared to an as-cast AZ91 alloy, friction stir back extrusion conducted at a rotational speed of 800 rpm and an extrusion speed of 20 mm/min resulted in a 44% increase in corrosion resistance in simulated body fluid (SBF).