Selective Laser Melting (SLM) has emerged as a transformative manufacturing technology, enabling the production of complex and highly precise components. However, processing high-strength aluminum alloys such as EN AW 7075 remains challenging due to issues including hot cracking, porosity, and pronounced microstructural instability.
This research addresses these challenges through SLM process parameter optimization and targeted modification of the alloy's chemical composition to improve its processability and mechanical performance.
The experimental work included thermodynamic calculations using Thermo-Calc software to predict phase stability and solidification behavior, as well as detailed characterization of the feedstock powder. Process parameters including laser power, scanning speed, and preheating temperature—were systematically varied to evaluate their influence on microstructure and mechanical properties. Initial results showed that conventional SLM conditions lead to significant defects. While preheating at 100 °C and 200 °C had only a limited effect, preheating at 400 °C changed the morphology of hot cracks, resulting in wider and less branched cracks. The results indicate that residual stresses were partially relieved through crack formation; however, preheating alone was insufficient to prevent cracking. To further enhance processability, the alloy composition was modified by adding silicon. This modification altered the solidification range and improved solidification behavior, resulting in a refined, more homogeneous microstructure with a significantly reduced tendency for hot cracking. Advanced characterization techniques-including Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Energy Dispersive Spectroscopy (EDS), and synchrotron X-ray diffraction-confirmed a fine-grained microstructure with reduced porosity and no visible cracks. Silicon addition also contributed to grain refinement and enhanced overall structural integrity. Following SLM processing, the material was subjected to heat treatment studies supported by Differential Scanning Calorimetry (DSC). Samples were heat-treated according to the T6 regime, then machined and tensile-tested. The modified alloy exhibited a homogeneous, fine-grained microstructure and significantly improved mechanical performance. The tensile strength of the as-built modified alloy reached up to 480 MPa. In contrast, the unmodified SLM EN AW 7075 alloy, due to defects such as cracks and porosity, did not reach the yield strength, with failure occurring at approximately 80 MPa. After T6 heat treatment, the tensile strength of the modified alloy decreased by approximately 10%, while the hardness decreased from 162.2 HV0.5 to 140.9 HV0,5.
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