The microstructure, mechanical properties and tensile deformation mechanism of rolled AlN/AZ91 composite sheets

Abstract

Due to the low ductility and poor formability, few studies were reported about the rolling behavior of magnesium matrix composites. In this study, in-situ AlN/AZ91 composite sheets were rolled at 400 °C with the total thickness reduction of 80 %. Compared with other rolled magnesium matrix composites, rolled AlN/AZ91 composite sheets in this study showed the good surface quality and better strength-ductility combination, which is expected to extend its application in industry. Although fully recrystallized α-Mg grains exhibited a basal rolling texture, there was no significant difference in mechanical properties along the rolling direction and transverse direction due to the weakening effect of AlN ceramic particles on the basal texture. During rolling, the high density of dislocations were formed around AlN ceramic particles owing to the residual plastic strain between AlN ceramic particles and AZ91 matrix, which promoted the continuous precipitation of γ-Mg17Al12 phase, so densely distributed nano-precipitates were obtained in the interior of the grains. TEM analysis reveals in-situ AlN ceramic particles not acted as the cracking source during rolling, which had a strong interfacial bonding with magnesium matrix, contributing to the good rolling capacity. Strengthening mechanism analysis suggests the high strength increment was mainly attributed to the dislocation strengthening and precipitation strengthening. For tensile axis along rolling direction and transverse direction, the dominated deformation mechanism at room temperature was pyramidal plane slip, leading to a relative high ductility.