Microstructural Analysis of Additive Manufactured Walls of AA5083 and AA4020 alloys produced by Cold Metal Transfer

Abstract

Additive manufacturing (AM), also known as 3D-printing, of metals has just recently become possible and fundamental studies are of high interest. In the current project wire arc additive manufacturing (WAAM) by cold metal transfer (CMT) have been used to build three walls with a single weld bead width and heights of about 3, 5- and 5.5 cm tall. Two of the walls are made of the Si rich Al-alloys AA4020 while the third is from the Mn-rich Al-alloy AA5083. Using the same processing parameters, it is seen that the alloy type strongly affect the shape of the walls. The Si-rich alloy pronounced signs of “sagging” while the AA5083 alloy was straighter with only a small bump mid-way up. The mechanical properties of the walls have been characterised by Vickers hardness- and tensile tests while the microstructure has been characterised by visible light microscopy and analytical scanning and transmission electron microscopy. The goal of the thesis has been to correlate the mechanical properties and the microstructural features observed. The microstructure analysis of the first wall of AA4020 alloy showed that the wall had layers of higher Si content with complex dendritic networks of crystalline silicon. These layers were measured to be harder in average (≈42HV) than those without the silicon enrichments (≈34HV). In addition, intermetallic particles of Al6(Mn,Fe) and Al(Mn,Fe)Si were found to be situated in between the dendrites. The third wall structure made out of the AA5083 alloy had short edge-fractures at the interface between two beads. In the same area was a region with high concentration of intermetallic particles. The tensile strengths were measured to an average value of ≈310MPa in the horizontal direction and ≈243 in the vertical direction, in which the weld beads are crossed, supporting too little heat during deposition.