HAADF-STEM and APT characterization on solute clustering and precipitation of Al-Cu-Mg based composites produced by additive manufacturing

High-performance precipitation hardening Al-Cu-Mg based alloys have been widely used in aerospace and automotive industries, especially at elevated temperatures (i.e. up to 250 °C). During the heat treatments, cluster clustering and precipitation very often occurs to provide strengthening effects for the high-performance Al alloys. Tailoring the solute clustering and precipitation is of great necessity to improve the performance of the Al alloys. However, the precipitates are not stable, in particular at elevated temperatures. Their strengthening effect becomes less or lost. Improving their thermal stability is therefore of great necessity. Alloying is one of the most important methodologies to improve their thermal stability. Indeed, Al-Cu-Mg-Ag alloy system, as an important Al alloy system, has been used to develop high strength Al alloys currently with plate-like Ω (AlCuMgAg) precipitate on the {111} planes and θ (Al ₂Cu) precipitate on the {001} planes. The high strength and thermal stability of these Al-Cu-Mg-Ag alloys has been attributed to the presence of the Ω precipitate and its propensity for interfacial segregation. Despite of its high strength of Al-Cu-Mg-Ag alloy system, it should be noted that Al-Cu-Mg-Ag alloy system has a significant hot tearing tendency and a serious segregation issue due to their large solidification range. An effective grain refinement can be used to solve the hot tearing and segregation issues. Although the addition of 0.1 wt.% TiB ₂ (as grain refiner) into Al-Cu-Mg-Ag based alloys (regarded as Al-Cu-Mg-Ag based composites) can refine grain size down to 200 µm, it is still not enough to reduce or avoid the hot tearing and segregation issues.