Development of tough and heat-resistant nanocrystalline aluminum alloy

Through the development of rapid solidification by atomization, new alloy designs, and new powder hardening techniques, Sumitomo Electric has developed a hyperfine-structured aluminum alloy called NANO ALUMI which features both heat resistance and a high degree of toughness. Its toughness is maintained by keeping the crystallization ratio of the volume of intermetallic compounds (IMCs) to 30% or less, and achieved extreme toughness by using very fine aluminum crystal grains of 1 μm or smaller. To achieve an IMC volume ratio of 30% or less, the volume of added alloy elements must be kept to 5 atom% or less, which in turn poses difficulties in the formation of the microstructure. It is already known, however, that Zr can be used to induce preferential nucleation in aluminum crystals through the formation of Al3Zr in the molten alloy. By using this technique during rapid solidification, we have demonstrated that extremely fine crystal grains can be formed even when using small amounts of added elements at the relatively slow cooling speeds used in industrial processes. In addition, by using high-frequency induction to heat aluminum alloy powder with a hyperfine structure formed in the above procedure, thus quickly hardening the powder through rapid heating, we were able to harden the alloy while retaining the microstructure. The high heat resistance of this alloy stems from that of the IMCs included in the alloy.