Microstructure and strengthening mechanisms of Zr-modified Al–Cu–Mg alloy processed by selective laser melting

Zr modification can significantly change the strengthening mechanisms of traditional heat-treatable Al alloys fabricated by selective laser melting (SLM). In this study, the effect of direct aging (DA) treatment on the microstructure and strengthening mechanisms of Zr-modified Al–Cu–Mg alloys fabricated by SLM was analyzed. The fine α-Al grains with an average size of approximately 1.1 μm in the as-fabricated samples were maintained after DA treatment. The S′-Al₂CuMg precipitates dissolved, and the secondary Al₃Zr-L1₂, 1.1 nm in radius, precipitated from the α-Al matrix after DA treatment. This led to a larger increase of 29 MPa in the contribution of precipitation strengthening compared with the increase of 5 MPa in the contribution of grain boundary strengthening after the DA treatment. In addition, a large number of Cu–Mg-rich and Cu–Mn-rich particles were found in the DA-treated sample, which offered dispersion strengthening. This work provides valuable insights for the development of Zr-modified 2000 series Al alloys applicable in additive manufacturing.