Foaming characteristics of Al–Si–Mg (LM25) alloy prepared by liquid metal processing

Abstract

LM25 (Al–Si–Mg) foams were made by melt processing route using Al foam scrap turnings as thickening agent in place of aluminium powder or Ca metal. The effects of foaming temperature and excess Mg content on melt expansion and cell structure were studied. The selection of foaming temperature significantly influenced foam decay. While severe collapse occurred at 670°C, foam decay is hardly observed at 640°C. Moreover, presence of excess Mg (3 wt-%) in this alloy enhanced collapse at 670°C, presumably due to its surface tension lowering effect. Despite foam collapse, a well defined and uniform cell size could be obtained at 670°C as compared to the foams obtained at 640°C. Uniaxial compression tests showed serrated plateau stress–strain behaviour with extensive localised but non-catastrophic damage leading to progressive breaking away of foam pieces. Overall, these experiments showed the potential to manufacture good quality LM25 foam using inexpensive Al foam turnings.