2022 年 63 巻 3 号 p. 286-293
This study aimed to understand the microstructural changes with reversion treatment in a 6061 aluminum alloy, such as dissolution of clusters formed during low temperature pre-aging. The specimens subjected to a solution treatment for 1.8 ks at 803 K and then pre-aged at 283 K for 604.8 ks were reheated under various temperature and time conditions. When reheated at 423 K, the hardness of the alloy specimen after reheating increased compared with that immediately after low temperature pre-aging. It was suggested that while the cluster dissolution hardly occurred during the reheating at 423 K, the formation of a strengthening phase from the supersaturated solid solution and transformation of some of the Mg–Si clusters formed during the low temperature pre-aging into the strengthening phase have occurred. In the case of reheating for 1 and 10 s at 523 K, which is commonly used as the reversion treatment temperature, the hardness of the final-aged specimen increased to the same level as that without low temperature pre-aging, indicating that the negative effect of two-step aging was mitigated. The mitigation of the negative effect was considered to be owing to microstructural changes, such as cluster dissolution, transformation of the Si-rich clusters, and precipitation of the strengthening phase during reheating at 523 K. Reheating above 573 K reduced the amount of age-hardening in the final-aging owing to the precipitation during the reheating. From these results, it is suggested that the adequate amount of solute atoms concentration in the matrix corresponding to that after a solution treatment could not be realized by the conventional reversion treatment.
