Enhancing high temperature strength of wire arc directed energy deposition Al-Cu heat-resistant aluminum alloy by precipitation of thermally stable phase

Al-Cu aluminum alloys are commonly used in high-temperature environments up to 200 degrees C due to their good heat resistance. In this study, we conducted a comprehensive investigation into the microstructure and mechanical properties of Al-Cu-Mn-Ni-Zr (205C) heat-resistant aluminum alloys fabricated using wire-arc directed energy deposition (WA-DED). The WA-DED 205C aluminum alloy exhibited a microstructure consisting of fine equiaxed grains in the interlayer zone and coarser equiaxed grains in the intralayer zone under both as-deposited (AD) and T6 heat-treated conditions. The average grain size showed a slight increase after heat treatment, measuring 20.5 mu m for AD samples and 23.4 mu m for T6 samples. Specifically, under the AD condition, continuous Al2Cu and Al7Cu4Ni second phases formed along the grain boundaries of the WA-DED 205C aluminum alloy, while a small number of 0' phases precipitated within the grains. After T6 heat treatment, most of the Al2Cu phases dissolved into the Al matrix, but the Al7Cu4Ni phases remained stable at the grain boundaries. This stabilization was beneficial in impeding migration and sliding of grain boundaries under high-temperature conditions. Furthermore, a significant number of fine 0' phases, 0' phases, Al3Zr phases, and Al20Cu2Mn3 phases precipitated within the grain, effectively hindering dislocation motion. The presence of the Al3Zr phase also prevented the coarsening of the 0' phase at high temperatures. At 300 degrees C, the WA-DED 205C aluminum alloys exhibited impressive mechanical properties. The ultimate tensile strength (UTS), yield strength (YS), and elongation (El) values for both the horizontal and vertical samples reached 199 MPa, 195 MPa, 7.8 % and 202 MPa, 198 MPa, 9.1 %, respectively. These results demonstrate that the high-temperature strength of WA-DED 205C aluminum alloys surpasses that of other Al-Cu heat-resistant aluminum alloys.