Modelling of SLM Additive Manufacturing for Magnesium Alloy

Abstract

Light-weight materials, such as magnesium and its alloys, have excellent mechanical properties, such as high specific strength, high specific modulus, good damping ability, thermal conductivity, etc. These properties make them a potential candidate for aerospace and automotive applications. The inability of the conventional manufacturing processes to manufacture precise and high-quality magnesium parts drives the exploring of new manufacturing techniques. In this study, the feasibility of additive manufacturing of AZ91D magnesium alloy using Selective Laser Melting (SLM) process has been investigated. Numerical modelling and simulations are performed to study the melt pool shape and size evolution, temperature and velocity fields, temperature gradients and cooling rate during the SLM of AZ91D powder, and the influence of the input laser power is described. The model considers conduction heat transfers and radiation heat losses from the powder bed surface, melting and solidification and convection in the melt pool. The simulation results provide preliminary insights of the complex physical phenomena occurring during SLM of AZ91D by describing the interaction between the laser source and the magnesium powder. The temperature and the velocity field were found playing a significant role in deciding the melt pool dimensions and geometry. An attempt has been made to describe the melt pool stability by calculating the ratios of melt pool length to width and melt pool width to depth. The spatiotemporal variation of temperature shows that very large temperature gradients and cooling rates (of the order of 10⁷ K/m and 10⁶ K/s, respectively) can be achieved. The high cooling rates are likely to result in the development of finer microstructure and so improved mechanical properties.