Mechanical properties and biodegradability of Mg-Zn-Ca alloys: homogenization heat treatment and hot rolling

In this study, Mg was alloyed with Zn and Ca to produce six different Mg-Zn-Ca alloys (designated as ZX alloys) by the gravity die casting method. Zn contents of the alloys were 1 wt., 3 wt., and 5 wt.% and Ca contents of the alloys were 0.2 wt. and 1.8 wt.%. Homogenization heat treatment was applied to all cast alloys. After that, a part of each homogenization heat-treated alloys was hot-rolled. Microstructure, mechanical properties, electrochemical and immersion corrosion behaviors at simulated physiological conditions of the heat-treated and hot-rolled alloys were compared. Increasing the amount of alloying elements (Zn and Ca) in Mg reduces grain size and improves the hardness. It was seen that the microstructure consisted of α-Mg as a matrix phase and intermetallic phases: Mg₂Ca phase for the alloy having Zn/Ca = 0.37 (ZX12) and Ca₂Mg₆Zn₃ phase for the other alloys. When the mechanical properties and corrosion rates of homogenized and hot-rolled alloys were compared, it was seen that hot-rolled ZX10-h (Mg-0.94Zn-0.16Ca) alloy can be considered as a fracture bone fixation plate material with its acceptable properties: 121 ± 2.1 MPa yield strength, 226 ± 3.7 MPa tensile strength, % 4.1 ± 0.2 elongation, and 0.062 mm/year immersion corrosion rate.