Development of open-porosity magnesium foam produced by investment casting

Abstract

High-porosity, open-cell AZ91 magnesium alloy foams of two pore sizes were fabricated by means of investment casting technology, using PUR foam patterns. Foam casting variables such as pressure, mould temperature and metal pouring temperature were thoroughly investigated to define the most optimal casting conditions. The mechanical properties of the fabricated foams were measured in compression tests. A potential application for the foams considered is temporary bioresorbable bone implants, therefore the mechanical properties of the foams were compared with those of cancellous bone tissue. Foams with smaller pore size and lower porosity (20 PPI and 80%–87%) exhibited mechanical properties in the lower regions of the cancellous bone property range (Young's modulus 36.5–77.5 MPa), while foams with higher pore size and porosity (10 PPI and ∼90%) were found to have insufficient compression strength (Young's modulus 11.65–23.8), but thickening their walls and lowering their porosity below 90% yielded foams with Young's modulus between 36.5 and 77.5 MPa. Foam fractures were also investigated to determine their collapse mechanism. A series of corrosion tests in stimulated body fluid was carried out to determine their applicability as a biomaterial. The Plasma Electrolytic Oxidation (PEO) process was used in a feasibility study to examine the microstructure and chemical composition of foams with protective coating.