UC Irvine

Additive manufacturing has developed as a strong tool in making parts with complex shapes and high qualities. The microstructure evolution of the AlSi10Mg alloy manufactured through Laser Engineered Net Shaping (LENS®) and Selective Laser Melting (SLM) AM techniques is studied through electron microscopy characterization. The solidified melt pools of both as-deposited samples exhibit a “fish scale” pattern that is inherent to the AM process. A very fine cellular microstructure is seen due to the high thermal gradients and cooling rates on the order of 103-106K/s. Eutectic silicon forms along the cell boundaries of the aluminum matrix. The rapid solidification and non-equilibrium conditions result in the formation of metastable phases. X-Ray Diffraction and Differential Scanning Calorimetry analysis were carried out to identify the phases in the as-deposited samples. In-situ and post-mortem TEM characterization were conducted to observe the formation of silicon and Mg2Si precipitates. The Mg2Si precipitates segregated along the cell boundaries in both of the as-deposited samples. The π-Al8Si6Mg3Fe phase was also observed to segregate along the cell boundary. High resolution transmission electron microscopy studies revealed a crystallographic orientation relationship between the [001] Al matrix and the [110] Si primary phase. A comparative study between the microstructure of the LENS® and SLM as-deposited samples revealed a finer microstructure in the as-deposited SLM sample. A conventional T6 heat treatment caused the cellular network to break down and the Si particles to coarsen. Microhardness tests were conducted on the as-deposited samples and heat-treated samples to correlate the mechanical properties with the microstructure. The hardness of the as-deposited samples was 105 HV which is higher than the hardness of a cast counterpart.