Deformation behavior near the grain boundary in the Al-Mg-Si alloy added copper

It is well known that an Al-Mg-Si alloy causes the intergranular fracture when this alloy is aged up to a peak-aging condition. We are studying about this behavior using a scanning tunneling microscope (STM) on the surface of deformed and fractured specimens, and found out a lot of results as follows. 1. There are many surface reliefs near grain boundaries. Its morphology is similar to the grain boundary sliding at a high temperature deformation. 2. An intergranular fracture is remarkable when there is many surface relieves near grain boundaries. 3. Three types of surface relief exist as follows: (1) Displacement to horizontal direction for a grain boundary (Type-H) (2) Displacement to vertical direction for a grain boundary (Type-V) (3) The mixture of both the Type-H and Type-V 4. A grain boundary that has maximum Schmidt factor deforms preferentially. 5. Fracture morphology is an intergranular ductile fracture. It is also known that the ductility is improved when copper is added to an Al-Mg-Si alloy We will report the result of STM study about deformation behavior near the grain boundary in an Al-1.0mass%Mg2Si alloy added 0.34% of copper in this work.