Minor Sc Addition Research Articles

Effect of minor Sc additions on structure, age hardening and tensile properties of aluminium alloy AA8090 plate

The grain structure, age hardening response, precipitate structure and tensile properties of AA8090 alloy plate without and with minor additions of Sc were investigated. Primary aluminide particles were present in all alloys. Sc additions ⩾0.43% resulted in refinement of the as-cast grain structure. Further investigations on 0.11% and 0.22% Sc containing alloys showed that the subgrain size was finer while the number density of nano-scale Al 3(Sc,Zr)/Al 3Li composite precipitates and the artificially aged hardness were higher for the Sc containing alloys. There was a marginal increase in the yield strength with a concomitant reduction in ductility with increasing Sc content in the alloys.

７０９０系アルミニウム合金急冷凝固材の組織と機械的性質に及ぼすＳｃとＺｒ添加の影響

Effect of minor addition of Sc + Zr has been studied on the structures and mechanical properties of rapidly solidified Al-9%Zn-2.5%Mg-1%Cu based alloys containing transition metals (Co, Fe, Fe+Ni, Mn). The amount of Sc and Zr addition was 0.2 mass% each. Rapid solidification was performed by gas atomizing and splat quenching onto a water cooled Cu single roll. Consolidation of the flakes was done by cold pressing, vacuum degassing and hot extrusion. Uniform distribution of Al 3 (Sc, Zr) particles was observed by TEM in the as-extruded P/M materials with Sc + Zr addition. Hardness became higher for the as-extruded P/M materials with Sc + Zr addition than those without addition even after annealing at higher temperatures. Uniform distribution of Al 3 (Sc, Zr) and η' particles were observed in the T6 treated P/M materials. The size of η' particle is smaller than Al 3 (Sc, Zr) particle. The T6 treated P/M materials with Sc + Zr addition showed higher hardness than the as extruded materials. However, T6 treated alloys with Sc + Zr addition did not always show higher tensile strength and fatigue strength than those without addition.

Characteristics of diffusion in Al-Mg alloys with ultrafine grain sizes

Equal-channel angular pressing (ECAP) was used to refine the grain sizes of pure Al and an Al–3 wt% Mg alloy containing minor additions of either Sc or Zr. Following ECAP, the grain sizes were in the ultrafine submicrometre range. Diffusion couples were prepared from the fine-grained material produced by ECAP and from the coarse-grained material without ECAP and these couples were used to measure the interdiffusion coefficients for Mg in an Al lattice. The results show the interdiffusion coefficient is larger in the fine-grained material and the experimental data from this couple agree with predictions from molecular dynamic simulations using the embedded-atom method. An activation energy of about 87 kJ mol-1 is estimated for grain-boundary diffusion of Mg in Al where this value is consistent with the expectations from measurements of the activation energy for lattice diffusion of Mg in Al. There is no evidence for enhanced diffusion in the boundaries produced by ECAP due, it is suggested, to the rapid equilibration of these non-equilibrium boundaries at elevated temperatures.