Size Dependent Melt And Relocation Behavior Of Aluminum Alloys In Surrogate Fire Environments

Aluminum alloys used abundantly in industries, such as aerospace, melt at temperatures (500—700°C depending on alloy) well below typical fire temperatures. Relocation of the melted aluminum is partly inhibited by aluminum oxide formation, which melts at much higher temperatures (about 2051°C) than aluminum itself. To model the effect of this self-healing oxide layer on the motion of melting aluminum requires further data on the behavior of melting aluminum. We present experiments which capture full-field position and temperature, while minimizing surface contact, using synchronous digital image correlation (DIC) and infrared (IR) thermometry on melting aluminum cantilever bars. Three bar sizes are studied to vary the relative importance of the oxide skin. Experiments show that each bar size has qualitatively different melting behavior, quantitatively different rate of collapse, and a “thermal slowdown” after passing 610°C regardless of size. All bars collapse significantly above the liquidus temperature, with large bars collapsing at higher temperatures than small bars. We describe a melt layer model, with different tiers of complexity where each tier explains more phenomenology. We show this model can explain observed phenomena, and provide mathematical theory amenable to other sizes, geometries, and loading.