Processing window for laser metal deposition of Al 7075 powder with minimized defects

There is a relative lack of data on the processing parameters suitable for laser metal deposition (LMD) of Al alloys, particularly high strength alloys. The objective of this study is to outline a systematic investigation to define the processing window for LMD of Al alloy 7075. Single linear tracks were fabricated by varying the powder mass flow rate, laser power, and scan speed according to a 33 factorial experimental design, in order to determine conditions that produce deposits with suitable cross section geometries. Single layer multi-track deposits were fabricated using parameters selected from the linear track experiments, and with varying track overlap values. Low energy input and powder deposition conditions were found to produce single track and multi-track deposits with porosity less than 0.3 and 1 %, respectively. Cuboid samples were produced using parameters selected from the single layer multi-track processing window. However, porosity of at least 4 % was observed in the cross section for all cuboid samples. Liquation cracking was not observed in the samples, despite clear signs of grain boundary liquation. Microcracks with a width of ∼1 μm were observed in the deposited material, and the results indicate that these are solidification cracks due to insufficient eutectic liquid to backfill and ‘heal’ incipient cracks. It is concluded that low energy density and powder mass deposition conditions can produce crack-free single layer deposits of 7075 with low porosity, but the elimination of interlayer porosity and microcracks in multi-layer deposits requires further study.