Non-equilibrium Al Alloy Fabrication And Powder Densification

In the investigation, non-equilibrium Al-based materials were prepared using rapid solidification techniques, including melt spinning and close-coupled inert gas atomization. Glass forming ability (GFA) of Al₈2Ni₁0Y₈ and Al-Ni-Ce-Fe-Cu system alloys were analyzed though melt spinning experiments. The effect of alloy elements on GFA was discussed. An assumption of the peculiar marginal GFA of Al-based alloys from the perspective of topological structure of atoms was presented. Based on the assumption, it was suggested that micro-alloying with small-sized atoms into the Al alloys might improve their GFA. Al₈2Ni₁0Y₈, Al₈6Ni₉Ce₂Fe₁Cu₂,Al₈7Ni₈.5Ce₃Fe₁Cu₀.5 powder were prepared by gas atomization and their microstructure, phase assembly, thermal stability and microhardness were tested. The cooling rates of the as-atomized Al₈2Ni₁0Y₈ powder and the melt spun Al₈2Ni₁0Y₈ ribbons were evaluated. The critical cooling rate for Al₈2Ni₁0Y₈ alloys to form amorphous structure was eatimated to be 4.591×10⁵ ℃/s based on the "quenchened-in nuclei" theory. Crystalline phases in Al-based amorphous alloys were systematically summarized and possible phase assembly in Al₈2Ni₁0Y₈ alloy was analyzed. The as-atomized Al₈2Ni₁0Y₈ powder was consolidated at five temperatures under ultra-high pressure. The microstructural evolution of bulk materials was examined and contribution to the densification from amorphous and crystalline phases was analyzed. There existed two competitive processes toward the densification behavior of as-atomized powder, namely viscous flow and crystallization of amorphous phases. Semi-quantitative analysis was made on these two processes and the contribution from the viscous flow to the densification process was more significant. The effect of heat treatment on the microstructure, phase assembly and mechanical of bulk Al₈2Ni₁0Y₈ alloys were also analyzed.