Additive manufacturing (AM) is considered a major technology capable to create components with shapes that are too complex to produce through traditional methods. During the last years the number of materials for AM rapidly increased, nevertheless, the majority of high-strength Al alloys cannot be successfully employed due to the occurrence of solidification cracks. Several AM techniques have been developing during recent years. This work is based on laser powder bed fusion (LPBF) technique that exploits the deposition of a metallic powder layer selectively melted by a high-energy laser beam. This work focuses on the processability, aging response and mechanical properties of an Al-Mg-Zr-Sc alloy produced by Laser Powder Bed Fusion. Primary precipitation of Al3(Sc,Zr) particles in the liquid phase are responsible for the heterogeneous nucleation of fine equiaxed grains, capable to suppress hot cracks. The microstructural features of the as-built alloy were investigated by optical and scanning electron microscopy, whereas the effect of the aging treatment on micro-hardness, residual stresses and mechanical properties was assessed. Micro-hardness tests showed a sharp increase after 2 hours of heat treatment and kept a high value for the whole duration of the isothermal curve, demonstrating high thermal stability of the alloy thanks to precipitates. Residual stresses suffered a decreasing trend upon aging, while yield strength and ultimate tensile strength increased up to 460 MPa and 489 MPa. Particular attention was given to the precipitation of Al3(Sc,Zr) particles during both solidification and heat treatments.
La manifattura additiva (AM) è considerata una delle principali tecnologie in grado di creare componenti con forme troppo complesse per essere prodotte con metodi tradizionali. Negli ultimi anni il numero di materiali per l’AM è aumentato rapidamente, tuttavia, la maggior parte delle leghe di Al ad alta resistenza non possono essere impiegate con successo a causa del verificarsi di cricche di solidificazione. Negli ultimi anni sono state sviluppate diverse tecniche AM. Questo lavoro si basa sul laser powder bed fusion (LPBF) che sfrutta la deposizione di uno strato di polvere metallica selettivamente fusa da un raggio laser ad alta energia. Questo lavoro si concentra sulla lavorabilità, la risposta all'invecchiamento e le proprietà meccaniche di una lega Al-Mg-Zr-Sc prodotta con Laser Powder Bed Fusion. La precipitazione primaria di particelle Al3(Sc,Zr) in fase liquida è responsabile della nucleazione eterogenea di grani fini equiassici, in grado di sopprimere le cricche a caldo. Le caratteristiche microstrutturali della lega as-built sono state studiate mediante microscopia ottica ed elettronica a scansione, mentre è stato valutato l'effetto del trattamento di invecchiamento sulla micro-durezza, stress residui e sulle proprietà meccaniche. Le prove di microdurezza hanno mostrato un forte aumento dei valori dopo 2 ore di trattamento termico e mantenuto un valore elevato per tutta la durata della curva isotermica, dimostrando un'elevata stabilità termica della lega dovuta ai precipitati. Gli stress residui hanno subito una tendenza decrescente con l'invecchiamento, mentre il carico di snervamento e il carico di rottura sono aumentati fino a 460 MPa e 489 MPa. Particolare attenzione è stata data alla precipitazione delle particelle di Al3(Sc,Zr) sia durante la solidificazione che i trattamenti termici.
Effect of aging on microstructure and tensile properties of m4p strength Al alloy produced by L-PBF
Cuccaro, Federico
2020/2021
Abstract
Additive manufacturing (AM) is considered a major technology capable to create components with shapes that are too complex to produce through traditional methods. During the last years the number of materials for AM rapidly increased, nevertheless, the majority of high-strength Al alloys cannot be successfully employed due to the occurrence of solidification cracks. Several AM techniques have been developing during recent years. This work is based on laser powder bed fusion (LPBF) technique that exploits the deposition of a metallic powder layer selectively melted by a high-energy laser beam. This work focuses on the processability, aging response and mechanical properties of an Al-Mg-Zr-Sc alloy produced by Laser Powder Bed Fusion. Primary precipitation of Al3(Sc,Zr) particles in the liquid phase are responsible for the heterogeneous nucleation of fine equiaxed grains, capable to suppress hot cracks. The microstructural features of the as-built alloy were investigated by optical and scanning electron microscopy, whereas the effect of the aging treatment on micro-hardness, residual stresses and mechanical properties was assessed. Micro-hardness tests showed a sharp increase after 2 hours of heat treatment and kept a high value for the whole duration of the isothermal curve, demonstrating high thermal stability of the alloy thanks to precipitates. Residual stresses suffered a decreasing trend upon aging, while yield strength and ultimate tensile strength increased up to 460 MPa and 489 MPa. Particular attention was given to the precipitation of Al3(Sc,Zr) particles during both solidification and heat treatments.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/183497