Influences of Fe and Si on notch toughness and tear resistance of Al-Mg-Mn alloy plates and welds

Abstract

Experiments were conducted to study effects of Fe and Si on notch toughness and tear resistance of Al-Mg-Mn alloy plates and welds. Notch toughness was evaluated by a ratio of notch-tensile strength to tensile strength (notch-tensile ratio), that of notch-tensile strength to yield strength (notch-yield ratio) and Charpy impact values and tear resistance by crack initiation and propagation energies in the Navy tear tests.The notch-tensile ratio, the yield ratio and the Charpy impact value of annealed plates and welds as well as crack initiation and propagation energies in the Navy tear test were reduced with increasing amounts of Fe and Si. Fe, Si and Fe + Si, if these contents were equal, had the similar influence on the notch toughness and the tear resistance. However, in a strict sense, the effect of Si was most notable.As the amounts of Fe and Si increased, the dimple pattern associated with ductile fracture gave way to the quasi-cleavage pattern associated with a relatively brittle fracture and the intergranular or interdendritic rupture was also noted. Fine lamellar cracks were observed in second phases containing Fe and Si. From these observations, it was considered that the crack initiation and propagation in the Al-Mg-Mn alloy plates and welds were closely related to the distribution of the second phases.