Mechanical Properties and In Vitro Corrosion of Biodegradable Open-Cell Zn Alloy Foams

In this study, three open-cell Zn (Al-Mg) alloy foams with two different pore sizes were prepared by an infiltration process that employs CaCl2 granules as space holders. The porosity of the three Zn alloy foams prepared by this method was in the range of 65-70%. The macrostructure and microstructure of the three foams were characterized systematically. Zn-5Al alloy foams showed a two-phase structure, mainly including the alpha-Al phase and eta-Zn phase. The Zn-1.5Mg alloy foam consists of the eta-Zn, Mg2Zn11 phase and MgZn2 phase. The Zn-3Al-1Mg alloy foam contains the eta-Zn phase, alpha-Al phase, Mg2Zn11 phase and Mg2Al3 phase. The compressive properties of three kinds of foams were conducted to investigate the stress-strain behaviours. The compressive strength of the as-cast alloy foam with a large pore size reached 16-20 MPa, which was higher than that of the as-cast alloy foam with a small pore size (11-14 MPa). After homogenization, the peak stress of the three alloy foams with large pore sizes increased to 18-27 MPa, especially for the Zn-1.5Mg alloy and Zn-3Al-1Mg alloy foams. The corrosion resistance and corrosion mechanism of the three Zn alloy foams were studied by immersion corrosion experiments in simulated body fluid. The corrosion rates of the three Zn alloy foams with small pore sizes at the initial stage of corrosion were higher than those of foams with large pore sizes. The maximum initial corrosion rate was 11.720 mm/year for the Zn-3Al-1Mg alloy foam with a small pore size, followed by 5.983 mm/year for the Zn-1.5Mg alloy foam. The lowest corrosion rate was 0.811 mm/year for the Zn-5Al alloy foam with a large pore size. The corrosion rate decreased with immersion time and remained stable. In addition, the galvanic corrosion effect was observed in the three alloy foams by corrosion morphology analysis. The alpha-Al phase and Mg2Zn11 phase were corroded prior to the eta-Zn phase.