Rapid densification of additive manufactured magnesium alloys via microwave sintering

Abstract

Binder jetting provides a highly versatile two-step technology for additive manufacturing of difficult-to-process materials, including magnesium (Mg) alloys. Sintering in conventional (CT) furnaces has been extensively performed as the post-printing process to densify 3D printed parts, and exploring alternative sintering approaches is considerably lacking. The current study aimed to present a detailed comparative analysis of the consolidation of as-printed parts in CT and microwave (MW) furnaces. Accordingly, binderless 3D printed parts made of Mg-5.06Zn-0.15Zr powder were subjected to CT and MW sintering for various isothermal holding times and their physical, mechanical, and chemical properties, as well as sintering kinetics models, were thoroughly evaluated and compared. It was revealed that MW results in a three-fold reduction in sintering time compared to CT sintering counterparts. Supported by the analysis of sintering mechanisms, the MW sintering process is not merely governed by the thermal effect in a similar way to CT sintering, but the non-thermal phenomenon originating from the conversion of electromagnetic energy contributes substantially to the densification of 3D printed Mg parts by triggering the viscous flow mechanism. Furthermore, results indicated that the Mg sample sintered in MW for 15 h has an interconnected porous structure with comparable density, pores features, elastic modulus, and compressive strength to those found in human cortical bone types. Overall, this work enlightens the great potential of MW sintering as an attractive alternative to reduce the energy consumption and shorten the lead time of the binder jetting technology.