Additively manufactured metallic materials exhibit excellent mechanical strength. However, they often fail prematurely owing to external defects (pores and unmelted particles) that act as sites for crack initiation. Cracks then propagate through grain boundaries and/or cellular boundaries that contain continuous brittle second phases. In this work, the premature failure mechanisms in selective laser melted (SLM) materials were studied. A submicron structure was introduced in a SLM Ag–Cu–Ge alloy that showed semicoherent precipitates distributed in a discontinuous but periodic fashion along the cellular boundaries. This structure led to a remarkable strength of 410 ± 3 MPa with 16 ± 0.5% uniform elongation, well surpassing the strength-ductility combination of their cast and annealed counterparts. The hierarchical SLM microstructure with a periodic arrangement of precipitates and a high density of internal defects led to a high strain hardening rate and strong strengthening, as evidenced by the fact that the precipitates were twinned and encircled by a high density of internal defects, such as dislocations, stacking faults and twins. However, the samples fractured before necking owing to the crack acceleration along the external defects. This work provides an approach for additively manufacturing materials with an ultrahigh strength combined with a high ductility provided that premature failure is alleviated.

The laser-based powder bed fusion (LBPF) process or commonly known as selective laser melting (SLM) has made significant progress since its inception. Initially, conventional materials like 316L, Ti6Al4V, and IN-718 were fabricated using the SLM process. However, it was inevitable to explore the possible fabrication of the second most popular structural material after Fe-based alloys/steel, the Al-based alloys by SLM. Al-based alloys exhibit some inherent difficulties due to the following factors: the presence of surface oxide layer, solidification cracking during melt cooling, high reflectivity from the surface, high thermal conductivity of the metal, poor flowability of the powder, low melting temperature, etc. Researchers have overcome these difficulties to successfully fabricate the different Al-based alloys by SLM. However, there exists no review dealing with the fabrication of different Al-based alloys by SLM, their fabrication issues, microstructure, and their correlation with properties in detail. Hence, the present review attempts to introduce the SLM process followed by a detailed discussion about the processing parameters that form the core of the alloy development process. This is followed by the current research status on the processing of Al-based alloys and microstructure evaluation (including defects, internal stresses, etc.), which are dealt with on the basis of individual Al-based series. The mechanical properties of these alloys are discussed in detail followed by the other important properties like tribological properties, fatigue properties, etc. Lastly, an outlook is given at the end of this review.