7xxx alloy fine grained sheets produced by a warm rolling method were investigated on their microstructures and bulk properties comparing with cold rolled sheets of AA7475 alloy. The warm rolled sheets deformed at 350 deg C kept the fine structure less than 3 mum after solution heat treatment. This structure was recognized by EBSP measurement as a subgrain structure with a high proportion of low angle boundary less than 15 deg while the cold rolled sheets had a high proportion of high angle boundary over 15 deg. It was also noted that the texture of the warm rolled sheets consisted mainly of the beta-fiber after solution heat treatment. A cross rolling method was applied for reducing anisotropy on polarized optical micrograph and led to successful results. In addition, it was found that the (011) component was formed strongly by the cross rolling. The (011) component was kept after solution heat treatment in the warm cross rolled sheets, but the cold cross rolled sheets formed a recrystallization texture without any strong components. The strength of the warm rolled sheets aged at 120 deg C increased about 10 percent comparing with that of the cold rolled sheets. The most important result in this study was that the property of resistance to SCC of the warm rolled sheets improved considerably. The reason of the above result was probably due to intermittent precipitation at grain boundaries on the warm rolled sheets in T6 condition.
展开▼
