AlSi10Mg is the most widely studied Al alloy used to produce components by Laser-based Powder Bed Fusion (LPBF), also known as Selective Laser Melting (SLM). Several papers have already investigated the effects of conventional heat treatment on the microstructure and mechanical behavior of the LPBF AlSi10Mg alloy, overlooking, however, the particular microstructure induced by rapid solidification. This paper reports on the effects of a T5 heat treatment and a novel T6 heat treatment on microstructure and mechanical behavior of the LPBF AlSi10Mg alloy, consisting of rapid solution (10 min at 510 °C) followed by artificial aging (6 h at 160 °C). The short solution soaking time reduced the typical porosity growth occurring at the high temperature and led to a homogeneous distribution of fine globular Si particles in the Al matrix. In addition, it limited the diffusion processes, increasing the amount of Mg and Si in solid solution available for precipitation hardening and avoiding the microstructural coarsening. As a result, the strength-ductility balance was improved by increasing both yield strength and elongation to failure, respectively of about 14% and 7% compared with the best solution among those reported in the literature for conventional T6 heat treatment of LPBF AlSi10Mg alloy.

The AlSi10Mg alloy is widely used to produce complex-shaped components by Laser-based Powder Bed Fusion (L-PBF); these parts, characterized by light structures and high specific strength, are currently employed in high-performance room temperature applications in the automotive and aerospace industries. However, it is important to increase the data concerning the high-temperature mechanical properties of the L-PBF AlSi10Mg alloy to spread its use. This study aims to fulfill the lack of knowledge by investigating the mechanical behavior at 200 °C, a representative condition of the average temperature of engine heads, of the L-PBF AlSi10Mg alloy subjected to a T5 heat treatment (artificial aging at 160 °C for 4 h) and an innovative T6 heat treatment (solubilization at 510 °C for 10 min and artificial aging at 160 °C for 6 h). The influence of high temperatures on the mechanical behavior of the L-PBF AlSi10Mg alloy was assessed by tensile tests, while microstructural and fractographic analyses were carried out to correlate the mechanical behavior of the alloy to its microstructure, and consequently explain the failure mechanisms. The ultrafine cellular microstructure, characterizing the T5 alloy, led to higher tensile strength than the homogeneous composite-like microstructure of the T6 alloy, which makes it very interesting for future application in the automotive and aerospace industries.

Few systematic studies on the correlation between alloy microstructure and mechanical failure of the AlSi10Mg alloy produced by laser-based powder bed fusion (L-PBF) are available in the literature. This work investigates the fracture mechanisms of the L-PBF AlSi10Mg alloy in as-built (AB) condition and after three different heat treatments (T5 (4 h at 160 °C), standard T6 (T6B) (1 h at 540 °C followed by 4 h at 160 °C), and rapid T6 (T6R) (10 min at 510 °C followed by 6 h at 160 °C)). In-situ tensile tests were conducted with scanning electron microscopy combined with electron backscattering diffraction. In all samples the crack nucleation was at defects. In AB and T5, the interconnected Si network fostered damage at low strain due to the formation of voids and the fragmentation of the Si phase. T6 heat treatment (T6B and T6R) formed a discrete globular Si morphology with less stress concentration, which delayed the void nucleation and growth in the Al matrix. The analysis empirically confirmed the higher ductility of the T6 microstructure than that of the AB and T5, highlighting the positive effects on the mechanical performance of the more homogeneous distribution of finer Si particles in T6R.

In the last decades, several anodizing processes for Mg alloys have been proposed to achieve a good wear and corrosion resistance combination. In particular, Electro-Chemical Oxidation (ECO) showed an improved dense and compact anodized layer compared to other anodizing processes carried out above the dielectric breakdown voltage, such as Plasma Electrolytic Oxidation (PEO). However, the influence of the ECO treatment on the tribological behavior and cyclic mechanical performance of Mg alloys has not been investigated yet. This paper reports on the influence of ECO on dry sliding behavior (vs. 100Cr6 bearing steel (block-on-ring contact geometry)) and rotating bending fatigue performance of the rare earth (RE)-containing Mg alloy EV31A-T6, comparing it with both untreated EV31A-T6 and PEO-treated EV31A-T6, used as benchmarks. The ECO-treated alloy showed improved tribological behavior (critical load for coating failure one order of magnitude higher and coefficient of friction 40% lower than for PEO) and fatigue strength (no decrease for ECO-treated samples compared to the untreated alloy, while PEO-treated samples induced a 15% decrease) due to the increased compactness and lower defectivity of the anodized layer, induced by the minimization of destructive arc discharges during coating growth. In addition, the ECO treatment significantly improved wear resistance compared to the untreated alloy, avoiding, at the same time, the decrease in fatigue strength, which typically occurs after PEO. Therefore, the ECO process can be applied to improve wear resistance without decreasing the fatigue strength of high-performance components.

The continuous research of new technologies and materials to reduce the CO 2 footprint has led to a significant interest in additive manufacturing (AM). In particular, the laser-based powder bed fusion (L-PBF) process represents one of the most attractive technologies currently available for producing complex-shaped components characterized by light structures and high mechanical performance. [1,2] Transportation and energy are probably the main industrial sectors that can significantly benefit from reducing the mass and size of mechanical parts manufactured by the L-PBF process to reduce their environmental impact. [3,4] Fuel injectors, heat sinks, mixing and swirling burner tips, pistons, gas turbines, and aerodynamic parts are, in fact, a few examples of possible L-PBF-produced components. [5][6][7] However, thin-walled and lattice design solutions require the continuous development of new thermally stable materials capable of withstanding the thermomechanical stresses caused by the severe operating conditions (high temperatures and long service times) occurring in automotive, aeronautical, aerospace, and energy applications. [8][9][10] Among the metals used in the L-PBF process, the Al-Si-Mg alloys represent an up-and-coming solution for producing structural components. [11] They meet both mechanical (high strength-to-weight ratio) and production requirements (good fluidity and weldability) compared to other Al-casting alloys, such as the heat-resistant Al-Cu and Al-Zn alloys. [12][13][14][15] The Si content close to the eutectic point reduces the solidification range and increases the powder bed's laser absorption, thus improving the melt pool (MP) fluidity and simplifying the printing process. [16] In addition, the high Mg content enables precipitation of the Mg 2 Si precursor phases during the printing process, further strengthening the Al matrix. [17,18] The AlSi10Mg alloy is currently the most common Al-Si-Mg alloy used in the L-PBF process. The cellular structure of the as-built (AB) L-PBF AlSi10Mg alloy consists of sub-micrometric cells of supersatured α-Al phase surrounded by a eutectic-Si network, which gives high hardness and tensile strength values at the expense of ductility. [19][20][21] However, as widely described by the authors in previous work, [22] the thermally activated diffusion processes alter the metastable microstructure of the AB alloy, acting on the size and morphology of the dispersed (nano-sized Si precipitates and precursors of the Mg 2 Si equilibrium phase) and aggregated (eutectic-Si network) strengthening phases. Consequently, given the complexity of the topic, the literature in recent years has mainly focused on the effects of process parameters and heat treatments on the microstructure and the mechanical properties at room temperature (RT) of the L-PBF