Fabrication of flame-retardant magnesium alloy hollow sphere with specific gravity less than one through atmospheric foaming

Metallic hollow sphere is a kind of lightweight metal foams. Most metallic hollow spheres have been made of iron. The authors have succeeded to fabricate Mg-Al-Zn alloy hollow spheres through inert gas foaming in the previous study. In the present study, magnesium alloy hollow spheres are fabricated through atmospheric foaming. The starting material was AZX912 flame-retardant magnesium alloy plates. AZX912 alloy precursors were produced through accumulative diffusion-bonding process. Magnesium hydride powder with the total amount of 1.0 mass% was used as a foaming agent. Foaming tests were carried out in atmosphere using a high-frequency induction heating system. The foaming process was in-situ observed by the digital video camera. The AZX912 alloy precursor expanded with increasing the heating time. As a result, AZX912 alloy hollow sphere with the porosity of 50% was obtained successfully. The hollow sphere easily floated on the surface of water because of the specific gravity of 0.91 and the closed-cell structure.