Influence of Heat Treatment and Inter-Layer Rolling on the Evolution of Micropores in the Additively Manufactured Aluminum Alloys

The application of wire + arc additively manufactured (WAAM) aluminum alloys has been restricted by the existence of porosity defect, which is generally detrimental to the mechanical properties. How to suppress the porosity of the WAAM aluminum components has drawn broad attention for safety service in recent years. inter-layer rolling was introduced in this study to eliminate micropores during the WAAM deposition for the Al-Cu6.3 and Al-Mg4.5 alloys. The distribution characteristics and individual morphology of micropores were revealed by the X-ray diffraction tomography (XRT). Key findings demonstrate that the number, volume, size and roundness of micropores of the two alloys decrease similarly with increasing rolling loads from 15, 30 to 45 kN. A high density of over 99.9% can be achieved under the 45 kN rolling. After the heat treatment, the homogeneous distribution of fine (around 5.3 μm) and spherical (0.70-0.74) micropores was realized for both the 45 kN rolled alloys. The mechanisms of this evolution include the reprecipitation of hydrogen pores, the formation of residual vacant voids and re-opening of unclosed pores. All the evaluated indicators of micropores in the 45 kN rolled + heat treated alloys were superior to the post-deposition heat treated state, the micropores evolution of which is dominated by Ostwald ripening or the formation of dissolution voids. The hybrid technique of WAAM + rolling + heat treatment (WAAM-RHT) has exhibited great potential in promoting the mechanical properties of the WAAM alloys. The results of this study may provide a theoretical guidance for the design of high-performance WAAM aluminum alloys.