FOLD FORMATION NEAR GRAIN-BOUNDARIES IN A N AGE-HARDENED ALUMINUM-ALLOY DEFORMED AT ROOM-TEMPERATURE

Localized deformation near grain boundaries in an Al-0.996 mass%Mg2Si- 0.395 mass%Si alloy was investigated by interference microscopy and sc anning tunneling microscopy. Both the displacement of scratch lines an d the steps at the grain boundaries were observed. The number of the g rain boundaries with displacement of scratch lines had a maximum at th e grain boundaries making angles of about 45 degrees to the tensile ax is. While a large numbers of the steps were observed at the grain boun daries making angles of near 90 degrees to the tensile axis. In both t ypes of grain boundaries, the direction of the maximum resolved shear stress (corresponding to F(max)) on a grain boundary plane is close to the moving direction of the grain boundary. When the step was formed simultaneously at two neighboring grain boundaries, fold was not obser ved. In such a case, the direction of F(max) on the grain boundary pla ne was slightly deviated from the moving direction. The values of F(ob s) (corresponding to the resolved shear stress on the grain boundary p lane in the moving direction) tended to increase with the amounts of s teps and displacements of scratch lines at the grain boundaries.