Preparation Of Closed-cell Magnesium Foams And Its Compressive Properties Research

Metal foam is a kind of composite material consisted of metallic matrix and gas bubbles. As a novel structural and functional composite material, metal foam can be applied to aerospace, transportation, automotive, construction machinery, metallurgical chemical, electronic communication and other fields. Magnesium and magnesium alloy foam has gradually caused the attention of researchers, because of the lower densities (1.74g/cm3) and high specific strength of its magnesium matrix.The basic preparation process of closed-cell magnesium foam was explored, and the effects of ignition-proof, thickening-agent, blowing agent and heat preservation to pore structure of magnesium foams were studied. And then a set of optimized parameters to fabricate uniform magnesium foam in our experiment condition was obtained:adding0.5wt.%Y and5wt.%Ca into the magnesium melt at750℃to ignition-proof:then adding3wt.%SiC particles of180mesh as thickening agent, stirring with900r/min to disperse SiC particles;and then2wt.%CaCO3was added into the melt at635-640℃, stirring for about20s with1000r/min to disperse CaCO3particles; take the magnesium into holding furnace quickly, and heat preservation at800℃for1-3min; At last, cool the magnesium foams in the air.To eliminate the defeat of creak, unusually large hole and non-bubble area in the magnesium foams, solution-sol method was used to coat SiO2passive layer on the surface of CaCO3particles. Thermal stability, composition and microstructure of the SiO2passive layer were studied by TGA-SDTA, XRD and SEM. And contrasting foaming experiments revealed that the dispersibility and wettability of coated CaCO3particles were improved, and its foaming speed was more placid. Moreover, ignition-proofed by.5wt.%Y and5wt.%Ca alloying, different cell size and homogeneous magnesium foams were prepared by adding various mesh of coated CaCO3without protective gas.The compressive tests results show that the stress-strain curve of magnesium foams contain three stages:elastic deformation, plateau region and condensation stage. And because the magnesium foams have uniform pore structure and small cell size, their compressive yield strength and specific strength are higher than aluminum foams with the same relative density. However, the magnesium foams are more brittle than aluminum foams, and the magnesium matrix should be strengthen and toughen.