Processing and characterization of crack-free 7075 aluminum alloys with elemental Zr modification by laser powder bed fusion

Abstract

High-performance engineering alloys, such as 7000 series aluminum alloys, suffer poor printability in laser powder bed fusion (LPBF) additive manufacturing. An enormous challenge lies in the suppression of solidification cracks caused by solidification shrinkage and thermal stresses. Porosity formation, as one of the main concerns for LPBF application, should also be avoided at the same time. In this study, aluminum alloy (AA) 7075 with and without Zr modification was additively manufactured by LPBF. Processing parameters of laser power and scanning speed, resulting in various volumetric energy density (VED), were experimentally determined to produce crack-free components with tailored microstructure. Optical microscopy was used to reveal how the crack density and porosity vary with VED. Scanning electron microscopy and transmission electron microscopy uncovered the detailed microstructure in the molten pool and the evolution of the elemental Zr addition. The results indicate that 1 w.t.% addition of elemental Zr in AA7075 led to lower crack density compared with 0.3 w.t.% addition. In 1 w.t.% Zr-modified AA7075, crack-free components were obtained under high VED. Fine equiaxed grains, instead of large columnar grains, were formed at the bottom of the molten pool boundary due to the existence of Al3Zr compound, which favored the nucleation of aluminum grains and elimination of cracks. The phenomenon of silicon segregation near cracks remained in Zr modified alloys, although its effects on cracking were suppressed. Spherical pores in the Zr-modified AA7075 increased due to the deterioration of fluidity by unmelted particles, which distracted the Marangoni flow as well. Sufficient laser energy input can increase the viscosity and ease the pores escaping. By optimizing parameters, crack-free AA7075 parts with low porosity can be manufactured through LPBF with Zr addition.

Development of a Novel Hybrid Suture Anchor for Osteoporosis by Integrating Titanium 3D Printing and Traditional Machining

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Material Behaviour of Three Blade Propeller Using Metal Additive Manufacturing Techniques

“…Reference [1] adopted the powder bed fusion method to prepare the implant and avoided implant and natural bone modulus mismatch with Beta-titanium alloys. Reference [2] experimented with the in uence of Zirconium reinforcement aluminium alloy (AA) 7075 in producing crack-free components in the laser powder bed fusion method. e results reveal that the increased quantity of reinforcement decreased the crack density.…”

Residual Stress Distribution in Selective Laser Melting of SS316L Parts

“…LPBF enables successive layer assembly with a laser beam as the heat source. e localized heat input in micron length and time scale induces rapid melting and consolidation through the formation of a molten metal pool [3]. Unfortunately, the enhanced thermal cycle of quick melting, cooling, and melt-back during SLM leads to higher residual stress gradients, which contribute to molten pool con guration, microstructure and mechanical properties microcracks, delamination, and component deformation, all of which are major challenges in the metal additive manufacturing (AM) community [4].…”