Microstructure and mechanical properties of an advanced Ag-microalloyed aluminum crossover alloy tailored for wire-arc directed energy deposition

Abstract

The implementation of wire-arc directed energy deposition requires the development of novel, process-adapted, high-performance aluminum alloys. Conventional high-strength alloys are, however, difficult to process as they are prone to hot-cracking. Crossover alloys based on Al-Mg-Zn combine good processability with good mechanical properties following artificial aging. Here, we present an effort to further improve the mechanical properties of Al-Mg-Zn crossover alloys using Ag microalloying. No cracks and few porosities were observed in the samples. The microstructure is dominated by fine and globular grains with a grain size ≈ 26.6 µm. The grain structure is essentially free of texture and contains fine microsegregation zones with ≈ 3–5 µm thickness of segregation seams. Upon heat treatment these microsegregation zones are dissolved and T-phase precipitates are formed as clarified by diffraction experiments. This precipitation reaction results in a microhardness of ≈ 155 HV0.1, a yield strength of 391.3 MPa and 418.6 MPa, an ultimate tensile strength of 452.7 MPa and 529.4 MPa and a fracture strain of 3.4% and 4.4% in transversal and in longitudinal directions, respectively. The gained results suggest that highly loaded structures can be manufactured by wire-arc directed energy deposition using the newly developed aluminum crossover alloy.