An investigation on the cause for the formation of blisters in the extruded aluminum channels for ladder application

A systematic study on determining the cause for the formation of blisters in the extruded alumi-num channels has been presented in this article. An extrusion of aluminum billets for making C-profile channels for ladder applications was carried out. It was found that the as-cast billets upon extrusion resulted in the formation of blisters on the inner surface of the channels. Blisters were found at the beginning and end of the extruded part. Initially, microstructure studies of the blister reveal the presence of a high amount of carbonaceous material, which is attributed to the lubricant used during the process. The confirmation test of repeating extrusion without lubrication revealed that blisters were forming even in absence of lubrication. Therefore a detailed study was carried out to understand the influence of extrusion process parameters like billet temperature, lubrication, and edge preparation. Amongst these, the effect of physical modification of the billet by cutting edges of the as-cast billets followed by extrusion yielded promising results. The effect of edge preparation has been explained based on the modeling and simulation of the casting process followed in the current work. The effect of casting leading to the formation of blisters has been elucidated.