Control of microstructural characteristics and mechanical properties of AlSi12 alloy by processing conditions of laser powder bed fusion

Abstract

To elucidate the possibility of controlling the microstructure and mechanical properties of Al–Si alloys additive-manufactured by laser powder bed fusion (L–PBF), the relationship among the laser conditions, microstructural characteristics (crystal grain, cellular microstructure, and solute Si in α-Al matrix), and tensile properties of L–PBF manufactured AlSi12 alloy samples was investigated. The crystal grain size and fraction of <001> oriented α-Al crystal grains toward the building direction increased as the laser power became higher and scanning velocity became slower. The width of cellular microstructure (sub–cell size) where the primary α-Al phase was surrounded by α-Al/Si eutectic microstructure increased as the laser power became higher and scanning velocity became slower. The refinement of microstructure was attributed to the solidification under high cooling rate, which was achieved by low laser power and high scanning velocity. The area fraction of Si phase analyzed from FE–SEM images tended to decrease as the laser power became higher and scanning velocity became slower, suggesting the possibility of solute Si concentration in α-Al matrix controlled by laser conditions. The STEM/EDS analysis revealed high concentration of solute Si in the α-Al matrix (above a solubility limit of 1.5 mol% in the Al–Si binary system) of L–PBF manufactured AlSi12 alloy samples and its concentration became higher in the sample manufactured using a higher laser power. The tensile tests of as–built AlSi12 specimens fabricated under various laser conditions were also performed. High strength and high ductility tended to be achieved when high power laser was applied in slow laser scanning velocity. The 0.2% proof stress was relatively higher when the laser scanning velocity was faster. The mechanical properties correlated with crystal grain size and sub–cell size rather than solute Si in the α-Al matrix. These results provide new insights to control mechanical performance of AlSi12 alloy via L–PBF processing parameters.