It is very popular to improve mechanical properties of Al-Mg-Si alloys by adding other element. For example, it is well known that addition of transition metals is useful because the refinement of grain size can be achieved, and with the addition of Cu to Al-Mg-Si alloy can increase the strength and hardness of the materials. Also, there are a few reports about the addition of Ag, which is particularly good for elongation. However, even now it has not been clarified yet why Cu and Ag are useful in improving alloys elongation. In this work, we have investigated the tensile behavior of excess Si-type Al-Mg-Si alloys, which contain Cu. The tensile test and hardness measurement were carried out. Scanning electron microscope (SEM) was used to investigate the fracture surfaces and individual crystallographic orientation. After small additional deformation, the crack was observed by the interface between higher Schmid Factor (S.F.) and lower S.F. grains. It was thought that this crack influenced fracture from fracture surface.