Factors that affect the properties of additively-manufactured AlSi10Mg: Porosity versus microstructure

Depending on the available laser powder bed fusion (LPBF) system, and the intended application, the use of highly-optimized LPBF parameters to fabricate near-perfect density alloys may not be feasible, economical or required. Thus, it is important to understand how sub-optimal density and microstructure can simultaneously affect the mechanical properties of alloys. Here we study the microstructure and properties of an AlSi10Mg alloy fabricated with sub-optimal parameters and investigate the effectiveness of post-processing by hot isostatic pressing (HIP) and T6 heat treatment. Defects were characterized using micro-computed tomography while the microstructure was analysed using transmission and scanning electron microscopy. The as-built microstructure features dendritically-arranged nano-crystalline Si particles that are favourable for high hardness, strength and impact toughness while T6 generally caused these properties to degrade. HIP was unable to close large defects due to trapped gases, which limited fatigue life improvements. Defects oriented normal to the loading axis (or parallel to the fracture plane) are very detrimental, but when oriented favourably, the alloy was still able to achieve comparable strength and ductility to results reported in literature for LPBF-fabricated AlSi10Mg alloys. Interestingly, the anisotropic nano-crystalline Si structures of the as-built alloy resulted in substantially improved toughness even when defects were oriented unfavourably.