Grain Structure Evolution of Al–Cu Alloys in Powder Bed Fusion with Laser Beam for Excellent Mechanical Properties

Abstract

Powder Bed Fusion with Laser Beam of Metals (PBF-LB/M) is one of the fastest growing technology branches. More and more metallic alloys are being qualified, but processing of aluminum wrought alloys without cracks and defects is still challenging. It has already been shown that small parts with low residual porosity can be produced. However, suffering from microscopic hot cracks, the fracture behavior has been rather brittle. In this paper different combinations of temperature gradients and solidification rates are used to achieve specific solidification conditions in order to influence the resulting microstructure, as well as internal stresses. By this approach it could be shown that EN AW-2024, an aluminum-copper wrought alloy, is processable via PBF-LB/M fully dense and crack-free with outstanding material properties, exceeding those reported for commonly manufactured EN AW-2024 after T4 heat treatment.

Crystallographic texture configured by laser powder bed fusion additive manufacturing process: a review and its potential application to adjust mechanical properties of metallic products

“…As pointed out by literature, LPBF process involves very fast heating, melting, solidification, and cooling phenomena associated with temperature gradients typically around 10 6 K/m [23,34,38,39]. Those mentioned conditions favor the solidification of large columnar (elongated) grains [5,11,23,25,38] especially when bigger G/R ratios are present (Figure 4b).…”

“…As pointed out by literature, LPBF process involves very fast heating, melting, solidification, and cooling phenomena associated with temperature gradients typically around 10 6 K/m [23,34,38,39]. Those mentioned conditions favor the solidification of large columnar (elongated) grains [5,11,23,25,38] especially when bigger G/R ratios are present (Figure 4b). The presence of this microstructure is essential to induce crystalline texture by synergistic epitaxial nucleation and growth between columnar or dendritic elongated grains, a mechanism recurrently reported by literature [9,[12][13][14]32,[40][41][42][43].…”

“…Therefore, the presence of {100} interfaces can induce epitaxial D <100> growing, especially if there are thermal conditions present favorable to the competitive growth of more stable interfaces. The energy extraction rate or heat flux (Q), which has the same direction, but with the opposite direction to the thermal gradient (G), influences crystalline growth in metals [4,5,[22][23][24][25].…”

“…Traditionally, the processing window is initially defined to obtain a highdensity product with scan speed (v) and laser power (P) the basic parameters that define it [2,9,30]. But the exact definition of a processing window depends on the final use in terms of geometric, physical, chemical, structural, and/ or mechanical requirements [23,27,[29][30][31][32][33].…”

In-Situ Alloy Formation of a WMoTaNbV Refractory Metal High Entropy Alloy by Laser Powder Bed Fusion (PBF-LB/M)

“…In comparison to parameter set PBF-LB/M B much smaller cracks are apparent in sample PBF-LB/M A. Cracking during PBF-LB/M is a common process-related defect and can have multiple causes. One mechanism, the so called hot cracking, which is related to the solidification of the alloy, is often reported for PBF-LB/M of e.g., Al wrought alloys like the EN AW 6xxx [ 44 ] or EN AW 2xxx [ 45 ] series. However, based on the crack structure visible in Figure 2 , hot cracking is excluded as the main cause of the cracks appearing in WMoTaNbV samples.…”