Hot cracking suppression by powder modification of an Al7075 alloy produced by laser powder bed fusion (L-PBF) and first insights in the improvement of its fatigue life

One of the main drawbacks of Laser Powder Bed Fusion (L-PBF) is the limited material palette currently available and the often poor fatigue performance of the resulting parts. Currently, the only high-performance aluminium alloy used to produce parts adapted for the aerospace industry using L-PBF is the Scalmalloy. However, it contains Sc, a scarce and expensive alloying element. L-PBF does not yet allow the production of such parts using more conventional 7xxx aluminium alloys. Indeed, these alloys exhibit severe cracking due to the high thermal gradients during L-PBF process. One way of suppressing hot cracking consists in the addition of grain refiner to the initial powder. In this study, a micrometric ZrH2 powder was added to Al7075 commercial prealloyed powder by the means of two different methods: a classical mechanical mixing and an innovative plasma coating. L-PBF process parameters were optimised and dense crack-free samples were produced. The microstructure and tensile properties for both addition techniques were thoroughly analysed and compared. A heat treatment leading to similar mechanical performances as the wrought Al7075 is currently being optimised. A first characterisation of the fatigue properties of these heat-treated L-PBF alloys and their improvements using friction stir processing as post-treatment are being assessed. Indeed, friction stir processing has been proven as a very successful post-processing method to increase the fatigue life of AlSi10Mg by a factor 100 [1]