STM observation of grain boundaries in Al-Mg₂Si base alloy deformed at room temperature

Surface topographies during tensile deformation at near grain boundaries were examined by Scanning Tunneling Microscopy (STM) in large- and small-grained Al-1.0mass%Mg₂Si-0.4 mass%Si alloy specimens having intergranular fracture. In both specimens, the steps at grain boundaries and the slidings of grain boundaries parallel to the specimen surface were observed. The height of the steps and the amount of slidings increased with the deformation. When either a step or a sliding occurred at a grain boundary, a fold was yielded at the triple point and had an individually different feature of surface topography. Frequency of fold formation with the amount of deformation in small-grained specimen was much lower than that of large-grained one. And the direction of the maximum resolved shear stress on a grain boundary plane is close to the moving direction of the grain boundary.