A Tailored AlSiMg Alloy for Laser Powder Bed Fusion

Abstract

The majority of aluminum alloys used for laser powder bed fusion are based on the aluminum-silicon system, particularly alloys containing 7 to 12 wt.% silicon and less than 1 wt.% magnesium. Silicon has a beneficial influence on melt viscosity during casting and laser additive manufacturing and prevents the formation of cracks. This study focused on the development of a new AlSi3.5Mg2.5 alloy for laser powder bed fusion with a Mg-Si content above 1.85 wt.% Mg 2 Si, which is the solubility limit of the α-aluminum matrix, and a subsequent heat treatment to adjust the mechanical properties with a wide range of strength and ductility values. The characterization of the microstructure was conducted by optical microscopy, scanning electron microscopy, transmission electron microscopy, and differential scanning calorimetry. The mechanical properties were determined by tensile tests and additional tight radius bending tests. The newly developed alloy was compared with AlSi10Mg and Scalmalloy ® . AlSi3.5Mg2.5 offers higher strength and ductility than AlSi10Mg, at comparable material costs. The mechanical properties can be adjusted in a wide range of values using a single step heat treatment. After direct ageing, the samples exhibited a ultimate tensile strength (UTS) of 484 ± 1 MPa and an elongation at break of 10.5% ± 1.3%, while after soft annealing, they exhibited a UTS of 179 ± 2 MPa and an elongation at break of 25.6% ± 0.9%.Metals 2020, 10, 514 2 of 13 coarsen [1,2]. Currently, there are only a few alternative processable aluminum alloys for additive manufacturing. These include casting alloys like AlSiCu alloys (EN AC-46xxx and EN AC-47xxx). These alloys offer high tensile strengths of up to 500 MPa with a low elongation at break of 5% [5][6][7].Many known alloys are difficult to process by laser powder bed fusion due to the formation of pores and cracks during solidification. These include medium and high strength wrought alloys of the alloy systems AlCu (EN AW-2xxx) [8][9][10], AlMgSi (EN AW-6xxx) [11,12], and AlZnMg (EN AW-7xxx) [13][14][15]. Known structural concepts for the development of alloys that are adapted to the additive manufacturing process use rare earth elements, such as scandium and zirconium, with varying content [16][17][18] or feature the addition of nanoscale grain refining additives to the known wrought alloys, such as the alloy EN AW-7075 [19]. When processed by laser additive manufacturing, both approaches lead to a combination with a high strength above 500 MPa combined with a good elongation at break of up to 15%. The disadvantages of these approaches are the high costs of scandium and the application of nanoparticles. A more detailed review of investigations into aluminum alloys for the LPBF process can be found in [20,21].The use of EN AW-6xxx alloys, whose strength is based on precipitation hardening, promises medium strength with a smaller decrease in ductility at low material costs. Artificial ageing leads to the formation of magnesium/silicon precipitates, which hinder dislocation mo...

Processability and Optimization of Laser Parameters for Densification of Hypereutectic Al–Fe Binary Alloy Manufactured by Laser Powder Bed Fusion

“…This more limited process window could be attributed to macroscopic cracking when the Al-15%Fe alloy powder is subjected to high laser powers and scan speeds (Figure 2a,c). Similarly, it is known to be difficult to process heattreatable wrought-type Al alloys (Al-Cu, Al-Mg-Si, and Al-Zn-Mg systems) using L-PBF, because those materials are highly sensitive to cracking during solidification [19][20][21][22][23][24][25][26][27][28][29]. The solidification cracks often propagate along the building direction (which likely coincides with the solidification direction) in a process called "hot cracking" [24,45], resulting in poor processability of high-strength Al alloys.…”

“…Optimization of the laser process parameters, in particular the laser power and scan speed, is required for the densification of Al-Fe alloy samples. In fact, the influence of L-PBF process parameters on porosity and cracking (L-PBF processability) had been extensively studied in the cases of Al-Si-based alloys [10,[16][17][18] and age-hardenable wrought-type alloys (the 2xxx, 6xxx, and 7xxx series) [19][20][21][22][23][24][25][26][27][28][29]. In comparison, similar research for the Al-Fe alloys remains limited [30], although a few reports considered application of the L-PBF process to the Al-Fe-based alloys [31,32].…”

Improvement in the PBF-LB/M processing of the Al-Si-Cu-Mg composition through the use of pre-alloyed powder

“…To date, aluminium alloys have attracted wide interest thanks to their excellent strength-to-weight ratio, but their considerable solidification shrinkage, tendency to oxidation, high laser reflectivity and the poor flowability of their powders make these alloys challenging to process by PBF-LBM [6][7][8]. Considering the non-printability by PBF-LBM of some of the traditional high-strength Al alloys, the challenge of creating new tailored compositions is still ongoing [9,10].…”

Microstructure, Mechanical Properties, and Fatigue Fracture Characteristics of High-Fracture-Resistance Selective Laser Melting Al-Ni-Cu Alloys

“…Churyumov et al [28] revealed that annealed SLM Al-Mg-Sc alloys exhibit excellent strength and ductility. Knoop et al [29] revealed that aging treatment parameters considerably affect the tensile strength of SLM Al-Si-Mg alloys.…”