Study of the damage of AA 8006 twin-roll cast thin sheets during forming of heat exchanger fins

A study of typical cracks which occur during forming operations of heat exchanger fins from strip-cast Al-Fe-Mn-Si (AA 8006) alloy sheets is presented. A number of failed heat exchanger lamellae, 0.10 to 0.25 mm thick, were examined by light and electron microscopy. Formability of the material correlates rather well with the grain structure and the distribution of second phase particles in the matrix. Sheets having good formability usually contain coarser intermetallic particles when compared with sheets torn during deep drawing operations. It was found that failure was due to surface grain size inhomogeneity in many cases, therefore a uniform grain structure is also favorable for improved formability.