The impact of post processing heat treatments on elemental distribution and corrosion properties of cold spray printed Al alloys

Abstract

In contrast to other additive manufacturing methods such as Wire Arc Additive Manufacturing or Laser Metal Deposition, the cold spray system designed by SPEE3D allows for structures to be printed at much lower temperatures. As a result, structures printed via cold spray often undergo post processing heat treatments which potentially alters the distribution of trace elements throughout the sample. The distribution of elements within these structures may then have a direct impact on the corrosion properties of these materials. The impact of post processing heat treatment parameters on the microstructure and distribution of Mg and Si trace elements within an Al alloy was investigated using cross section analysis of samples by SEM-EDS. From an Al powered feedstock, alloys were printed using SPEED3D’s LightSPEE3D printer utilising air as the carrier gas, at 30 Bar and 500°C; various post processing heat and water quench treatments were then applied. Results reveal a reorganisation of Mg (which subsequently becomes oxidised) towards the edges of pores, regions typically with a higher surface energy. This is in direct contrast to the largely homogenous distribution of Mg in samples which did not undergo post printing heat treatments. The addition of charcoal during the heat treatment process also resulted in the redistribution of Si within the sample, and the creation of silicon carbide structures. The impact of reorganisation of Mg within the sample as well as the creation of silicon carbide structures on the selective corrosion of these materials was then investigated by potentiodynamic corrosion testing and electrochemical impedance spectroscopy.