Precipitation in a 2xxx series Al-Cu-Mg-Zr alloy fabricated by laser powder bed fusion

Abstract

The processing of conventional alloys by laser-based additive manufacturing can be challenging, particularly for alloys prone to hot cracking. However, additive manufacturing offers the possibility to produce novel alloys with improved properties, which cannot be achieved by other processing methods.Although several studies have demonstrated the positive influence of Zr addition on crack prevention of Al alloys tailored to additive manufacturing, its influence on the formation of strengthening precipitates in 2xxx alloys, remains largely unexplored. This work investigates the microstructure of a Zr-modified 2xxx AlCuMgZr alloy fabricated by laser powder bed fusion, with a particular emphasis on the precipitation of phases induced by the post-processing heat treatment, and their effects on mechanical properties.The Zr addition successfully allows the consolidation of crack-free, dense material (>99.5%). The microstructure is characterized by fine, equiaxed grains (0.5–3 μm) which result from Al3Zr-induced grain nucleation, with the grain boundary covered in eutectic S-Al2CuMg. After optimized three-step heat treatment, nm-sized L12-Al3Zr as well as S-Al2CuMg rods strengthen the alloy, and lead to microhardness, young's modulus and yield strength of ∼1410 MPa, ∼82 GPa and ∼340 MPa, respectively. The results provide a basis for the understanding and further development of 2xxx alloys tailored to additive manufacturing.