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Solidification of metal foams

enlarged view

Area expansion and temperature as a function of time for foaming of AlSi6Cu4 alloy. The temperature defines three stages of foaming – heating, holding and cooling. The holding time is 100 s followed by natural cooling.

While SE1 is mainly caused by the production of hydrogen from blowing agent, SE2 is a result of precipitation of dissolved hydrogen from the metallic melt during solidification. Cooling rate has significance influence on SE1: increases with decreasing cooling rate. The kinetic interplay of shrinkage of the gas present inside the foam, the out-diffusion of hydrogen to the surrounding space and the production of hydrogen from the blowing agent is the reason of SE. When SE has high value, it induces defects in the foam structure which is caused by SE-induced ruptures during solidification.