Mechanical properties, corrosion behavior and biocompatibility of orthopedic pure titanium-magnesium alloy screw prepared by friction welding

The dissimilar joining of biodegradable magnesium alloy to pure commercial titanium by rotational friction welding with rotational speeds of 1100, 1200 and 1300 r/min for the production of bio-screw was investigated. The metallographic analysis revealed that a good joining was obtained at the Ti/Mg alloy joint. On the magnesium alloy side, various regions such as the weld center zone (WCZ), dynamic recrystallization zone (DRX), thermo-mechanically affected zone (TMAZ) and partially deformed zone (PDZ) were observed. The highest tensile and shear strengths were 173 and 103.2 MPa, respectively at a rotational speed of 1300 r/min. The Ti/Mg alloy dissimilar friction welded joint failed at the vicinity of the intermetallic zone containing Ti3A1 phase. The hardness values from the base metal magnesium alloy to the joining point increased mainly due to grain refinement (8.57 tm in diameter) and the presence of titanium particles, while the hardness values were constant on the titanium side. It was also found that the corrosion rate of the Ti/Mg alloy joint was higher compared with that of the Ti and Mg alloy from the immersion studies. Additionally, the sample with a rotational speed of 1300 r/min showed better biocompatibility and a cell viability of 98.12% due to better corrosion resistance.