Abstract
The effects of types of molds and sorts of additional elements on the cast structure and hardness of hyper-eutectic Al-Mn alloys were studied. The additional elements used were such considered to refine the primary crystals of the alloys, i.e., each 0.5-1% addition of Fe, Nb, W, Zr, V, Cu, Mg, Si, Ca, etc. The change of hardness by heat-treatment of these alloys was also examined.
The results obtained were as follows.
(1) It was found that the microstructures of Al-4% Mn Alloys were different from each other in sand mold castings, metallic mold castings, and die castings. It was observed that primary crystals were larger and angular in sand mold castings, but were finer in metallic mold castings. In die castings, especially, fine network microstructure, which would be regarded as supersaturated α solid solution, was observed.
(2) Remarkable variation was not observed on hardness of sand mold castings according to the sorts of additional elements. There was observed a difference of hardness between sand mold and metallic mold castings.
(3) Slight age-hardening was recognized on die castings having network microstructures when annealed at 360-500°C.
