Development of novel high temperature aluminum alloys

Abstract

High temperature aluminum alloys can possess a desirable combination of specific strength, corrosion resistance, electrical and thermal conductivity, and creep resistance at temperatures in excess of 300 °C. However, the selection of commercial high temperature aluminum alloys is quite limited due to material cost and/or challenges in solidification processing of the highest performance alloys. In the present work, the high temperature aluminum alloy 8009 (Al-4.4Fe-0.6V-1.8Si, at.%) was modified to create alloys containing face-centered cubic Al (FCC-Al) and the α-phase intermetallic, and remove the deleterious h-phase intermetallic. The crystal structures of the competing h and α-phase intermetallics in 8009 and related alloys were characterized using powder diffraction. The differences in atomic structure of the two phases were used to predict alloy modifications that promote the α-phase and mitigate h-phase formation. Atomistic and thermodynamic modeling were used to determine novel FCC-Al + α-phase alloy compositions. Various compositions of Al-(Co-Fe-Mn-Cr-V-Mo)-Si FCC-Al + α-phase alloys were experimentally investigated to verify the modeling results. The alloy Al-4.4Fe-0.2V-0.4Mo-2.3Si (at.%) was identified as a promising dispersoid-strengthened FCC-Al + α-phase alloy and the Al-Fe-Mn-Cr-Si alloy system was chosen as a model system for studying the FCC-Al + α-phase eutectic solidification behavior and assessing its mechanical properties. The solidification behavior of Al-Fe-Mn-Cr-Si alloys was investigated using chill casting and autogenous welding. Microstructure-processing maps were generated from these experiments. Mechanical properties were assessed using microhardness, compression, and in situ tensile testing. Al-Fe-Mn-Cr-Si FCC-Al + α-phase eutectic alloys were found to have mechanical properties that meet or exceed those of most existing, conventionally-processed high temperature Al alloys at temperatures up to 370 °C. Additionally, these alloys can be processed under conditions similar to conventional processing routes like strip casting and die casting, as well as additive manufacturing. Because of their enhanced microstructural stability relative to most commercial high-temperature Al alloys, FCC-Al + α-phase eutectic alloys are a promising new class of aluminum alloys.