Precipitation during recrystallization of Al-Mn alloys

• Published in: Journal of Japan Institute of Light Metals Vol. 21; no. 7; pp. 444 - 455
• Main Authors: NAGAHAMA, Katsusuke, TAKAHASHI, Masahiro, MIKI, Isao
• Format: Journal Article
• Language: Japanese; English
• Published: The Japan Institute of Light Metals 1971
• ISSN: 0451-5994; 1880-8018
• DOI: 10.2464/jilm.21.444

This study was undertaken to investigate the precipitation phenomena during recrystallization of supersaturated and deformed Al-Mn alloys. Specimens used were Al-1.34wt%Mn and Al-1.29wt%Mn-0.05wt%Si alloys. They were cold-rolled after solution treatment at 640°C, and were heated at several temperatures of 300600°C. Experiments were carried out by measurements of hardness and electrical resistivity and electron microscopy. The results obtained were summarized as follows: (1) Precipitation of manganese was accelerated by cold working. This effect was particularly marked when the specimen was anncaled at temperatures not higher than 400°C. (2) At lower temperatures(≤400°C), precipitation process reached near the equilibrium state before the end of recrystallization process. Therefore, the nucleation and growth occurred in dislocations or dislocation cell structures (subboundaries). Therefore, the acceleration of precipitation would be due to the easier nucleation in these lattice defects and easier growth by pipe diffusion. (3) At higher temperatures (≥450°C), precipitation occurred after the end of recrystallization.In this case, the nucleation took place also in the lattice defects, but the growth occurred in the recrystallized matrix. Therefore, the acceleration of nucleation was only due to the easier nucleation. (4) The addition of 0.05wt%Si accelerated the precipitation process of deformed Al-Mn alloys and made precipitates finely distributed. This acceleration was supposed to be related with the retardation of recrystallization due to the finely distributed precipitates. (5) Almost all the precipitates were identified as Al6Mn in the both alloys. However, Al6Mn precipitates were in globular form at lower temperatures and rectangular thin plates at higher temperatures.It was the first identification ever experienced in the world that the rectangular thin plates of Al6Mn precipitates were observed in the from of rectangular thin plates. (6) The crystallographic relation between the rectangular plates and aluminum matrix was found to be Al// Al6Mn and {111}Al//{110} Al6Mn and their habit planes were supposed to be{111}Al. The rectangular plates seemed to be coherent with aluminum matrix at the earlier stage of precipitation.