Abstract
A modified strain-induced melting activation (SIMA) process is shown to improve high-temperature formability. The microstructural characteristics of the spheroidized grains of SIMA-processed alloys affect high-temperature formability. The effects of hot extrusion parameters and chemical composition on the evolution of spheroidized grains were investigated using several 6xxx series aluminum alloys subjected to a modified SIMA process. The results show that 6066 aluminum alloy is the most suitable alloy for the SIMA process, as it contains sufficient Mg, Si, Cu, and Mn. Adequate amounts of Mg, Si, and Cu lead to a high liquid fraction, and a sufficient addition of Mn inhibits grain growth. Proper hot extrusion parameters are essential, because initial fine and uniform recrystallized grains lead to fine and uniform globules. The phases at the global grain boundaries of 6066 aluminum alloy are eutectic phases of Al and Si, Al and Mg2Si, and Al and Al2Cu, as analyzed using transmission electron microscopy.
Highlights
The semi-solid metal forming process is a hybrid net-shape process that combines the advantages of forging and casting [1,2]
The two major differences between the traditional strain-induced melting activation (SIMA). Process and this modified SIMA process are: (1) this modified SIMA process uses severe hot extrusion instead of cold work to introduce a large amount of strain energy; and (2) this modified SIMA process uses a salt bath instead of an air furnace to improve heating uniformity and reduce heating time
Dynamic recrystallization occurred in both aluminum alloys in the hot grain growth dynamic recrystallization, since increases thedue temperature of recrystallization extrusion step, after but the grain sizes of the two alloys areitnot identical to Mn retarding grain growth after dynamic recrystallization, since it increases the temperature of recrystallization [10,13,14]
Summary
The semi-solid metal forming process is a hybrid net-shape process that combines the advantages of forging and casting [1,2]. The steps of common and traditional SIMA process are: (1) casting, which produces a dendritic structure; (2) hot work, which disintegrates the initial structure; (3) cold work, which introduces strain energy into the alloy; and (4) heat treatment, which makes the material recrystallize and partially melt at the temperature of solid–liquid coexistence. It is a three-step process because three steps of casting materials are required in order to obtain globular grains. Several extruded 6xxx aluminum alloys were used to investigate the effects of components and hot extrusion parameters on spheroidized grains in the modified SIMA process. Mechanism of elemental diffusion are analyzed using transmission electron microscopy (TEM)
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