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The fracture behaviour of two AA6016 aluminium alloys with different
magnesium content was studied after uniaxial tensile tests. SEM fractographs of
both materials suggest two types of failure mechanisms. The first is characterized
by a sequence of events, i.e. void initiation, growth and coalescence on
constituent particles, whereas the second one can be identified as ductile
intergranular failure. The second type of failure is observed more often in the
aluminium alloy with higher magnesium content. In both aluminium alloys,
secondary cracks were found close to the fracture surface on the cross-section
plane of the tensile sample. Orientation contrast microscopy images show that the
secondary cracks were formed either by an intergranular failure mechanism or by
local plastic instabilities such as shear bands which subsequently progress into
cracks. The higher magnesium content gives higher strength but reduces the
ductility by weakening the grain boundaries.