Abstract
High purity Al-Mg-Si base alloys often exhibit low tensile ductility and typical grain boundary fracture occurs when aged to maximum strength levels. The influence of cold work and aging on the ductility and the fracture behaviour of high purity Al-Mg-Si base alloys has been investigated to prevent the grain boundary fracture and to improve the low ductility of the alloys. Marked improvement in the ductility of coarse grained alloys can be attained by proper cold work and aging, and the fracture mode changes from brittle grain boundary fracture to ductile transgrannular fracture. These phenomena are observed only in the coarse grained alloys and not in the fine grained alloy containing Cr. Preaging treatment after quenching is undesirable because of a decrease of the ductility. Marked improvement in the ductility is attributed to the absence of PFZ along grain boundaries, the suppression of coarse grain boundary precipitates and the precipitation of coarse intermediate precipitates in the matrix.
