研究論文
リン酸塩を含む溶剤による過共晶 Al-Si 合金の初晶 Si 微細化に関する研究
1972 年 44 巻 3 号 p. 157-165
詳細
1972 年 44 巻 3 号 p. 157-165
Coarse primary silicon in the cast structure has a bad effect on the mechanical properties such as tensile strength, elongation, impact resistance, etc. of hypereutectic aluminum-silicon alloys. There are many reports concerning the refining method of primary silicon in hypereutectic aluminum-silicon alloy. The flux for refinement of primary silicon developed by the authors, recently, consists of sodium hexametaphosphate (NaPO3)6 and aluminum oxide (Al2O3). Al-20%Si alloy bath melted with 99.99% aluminum and 99.98% silicon was covered with the flux at 800°C and kept for 10 to 15 minutes in this state, after which it was cast into iron or shell mold at 750°C.
The refinement of primary silicon by the flux treatment was investigated by measuring silicon grain size all over the specimen cast into an iron mold taking longitudinal and cross sections. On the other hand, the specimens cast into a shell mold were used for the test of tensile strength, elongation and hardness of Al-20%Si alloy refined with the flux.
The results obtained are as follows :
1) The refinement of primary silicon with the flux which consisted of sodium hexametaphosphate and aluminum oxide at the ratio of 8 to 1, was remarkable with the refined primary silicon size about 20 microns. A uniform structure was observed throught the specimen because of decreasing mass effect by the flux treatment.
2) The alloys treated with the flux have high values of tensile strength and elongation, but low values of hardness.
3) When metallic sodium effective for refining eutectic structure was added to the flux, it was found that the flux must be treated just after the addition of metallic sodium so as to prevent the coarsening of primary silicon by sodium.
4) Hygroscopic property of the fused flux is equivalent to about one hundredth to one three hundredth of the mixture of sodium hexametaphosphate and aluminum oxide.
5) The flux is advantageous, because only a small amount, that is 1 to 2% of the molten alloy spread over the surface of the molten bath, is sufficient to refine alloys.
