High-temperature deformation resistance and forming behavior of two-step SIMA-processed 6066 alloy

Abstract

The aims of this study were to investigate the effects of a modified two-step strain-induced melt activation (SIMA) process on the high temperature formability of 6066 Al alloy, and to understand the compressive and tensile properties of the alloy such processed. For these purposes, the forming test which compressed a cylindrical rod into a screw nut was conducted at 550°C, while the compressive and tensile tests were conducted at 550°C and the vicinity. The high-temperature tensile data show that phases on globule boundaries can cause the SIMA-processed alloy to break by integranular fracture, and thus the tensile ductility cannot compete with the alloy in hot-extruded condition to have dynamic recrystallization during tensile deformation. The high-temperature compression test shows that the flow resistance can be decreased by the SIMA process to the level lower than that of the fully annealed alloy. In terms of compressive microstructure, the SIMA-processed alloy is composed of three zones: (1) large deformation zone with flattened structure in specimen center, (2) free deformation zone with globular grain structure near the top and bottom edges, and (3) a transition zone between the above two zones. Finally, the forming test shows that SIMA process can decrease flow resistance by about 25–30%. When a SIMA-processed alloy has sufficient liquid fraction and appropriate globule size, its ability of metal flowing can be significantly increased to have superior high-temperature formability.