Microstructure Evolution and High-Temperature Compressibility of Modified Two-Step Strain-Induced Melt Activation-Processed Al-Mg-Si Aluminum Alloy

Chia-Wei Lin, Fei-Yi Hung, Truan-Sheng Lui, Li-Hui Chen
2016 Metals  
A two-step strain-induced melt activation (TS-SIMA) process that omits the cold working step of the traditional strain-induced melt activation (SIMA) process is proposed for 6066 Al-Mg-Si alloy to obtain fine, globular, and uniform grains with a short-duration salt bath. The results show that increasing the salt bath temperature and duration leads to a high liquid phase fraction and a high degree of spheroidization. However, an excessive salt bath temperature leads to rapid grain growth and
more » ... rain growth and generates melting voids. The initial degree of dynamic recrystallization, which depends on the extrusion ratio, affects the globular grain size. With an increasing extrusion ratio, the dynamic recrystallization becomes more severe and the dynamic recrystallized grain size becomes smaller. It results in the globular grains becomes smaller. The major growth mechanism of globular grains is Ostwald ripening. Furthermore, high-temperature compressibility can be improved by the TS-SIMA process. After a 4 min salt bath at 620˝C, the high-temperature compression ratio become higher than that of a fully annealed alloy. The results show that the proposed TS-SIMA process has great potential. two steps after casting. The two major differences between the traditional SIMA process and the proposed two-step SIMA (TS-SIMA) process are: (1) the proposed TS-SIMA process uses severe hot extrusion instead of cold work to introduce a large amount of strain energy; (2) the proposed SIMA process uses a salt bath instead of an air furnace to improve heating uniformity and reduce heating time. The procedure of the modified TS-SIMA process is shown in Figure 1b. Metals 2016, 6, 113 2 of 13 is done via three steps to obtain globular grains. This study proposes an improved SIMA process that has two steps after casting. The two major differences between the traditional SIMA process and the proposed two-step SIMA (TS-SIMA) process are: (1) the proposed TS-SIMA process uses severe hot extrusion instead of cold work to introduce a large amount of strain energy; (2) the proposed SIMA process uses a salt bath instead of an air furnace to improve heating uniformity and reduce heating time. The procedure of the modified TS-SIMA process is shown in Figure 1b . Figure 1. Procedures of (a) traditional three-step strain-induced melt activation (SIMA) process and (b) modified two-step SIMA process. RT: room temperature.
doi:10.3390/met6050113 fatcat:mdes73tkbvefbme5hcqkxl4g4q