Formability and microstructure of laser powder bed fused AlSi10Mg alloy sheets under various deformation conditions

The large thermal gradient and high cooling rate generated in the fabrication of complex thin-walled components by laser powder bed fusion (LPBF) may cause uncontrolled deformation and reduce dimensional accuracy. The existing preheating-assisted LPBF process is still difficult to fabricate complex thin-walled components to large size (e.g., reach 800 mm) with the required dimensional accuracy and structural properties. To solve this problem, a novel integrated process of LPBF and hot metal gas forming (HMGF) was proposed in this study to fabricate complex thin-walled components. In this process, a preform with a geometrical shape close to the final component is first fabricated by LPBF process, and then this preform is formed into the desired shape by HMGF process. The hot formability of the LPBF AlSi10Mg sheets was investigated to verify the feasibility of this novel forming process. Also, the hot formability was compared with that of gravity cast (GC) AlSi10Mg sheets. The microstructure, phase structure, uniaxial and biaxial hot formability were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), hot uniaxial tensile and hot biaxial gas bulging experiments, respectively. The results indicated that the cellular microstructure of the LPBF AlSi10Mg gradually disappears with the increase in temperature. The LPBF AlSi10Mg sheet exhibits superior mechanical properties to the GC AlSi10Mg sheet due to the mixed strengthening mechanism among strengthening phase precipitation, grain structure and dynamic recrystallization (DRX) degree. For instance, the former demonstrates a total elongation (obtained from hot uniaxial tensile tests) of 81.2% and an ultimate bulging height (obtained from the hot biaxial gas bulging tests) of 12.16 mm; in contrast, the latter's elongation and bulging height are 56.2% and 9.26 mm, respectively. Moreover, the LPBF AlSi10Mg sheet shows more uniform deformation than the GC AlSi10Mg sheet during the bulging tests. The feasibility of forming the LPBF-fabricated preform by HMGF process was confirmed. This lays a foundation for the integrated process of LPBF and HMGF to fabricate complex thin-walled components.