Post-treatment of LPBF AlSi10Mg for fatigue resistance enhancement

The development of additive manufacturing (AM) is opening new possibilities and new fields of application. The use of AM structural parts is already a reality in some cases [1]. However, when aiming at high end and demanding sectors, such as the aeronautic and aerospace industries, in the instances where the structural aspect plays a critical role, the use of metal AM components is still limited. AM parts often have defects (porosity and roughness) that influence fatigue resistance in a negative way. There is a need to get rid of these defects typical of the AM technology. Efforts to achieve this can consist on AM manufacturing parameters optimisation. These parameters can be tuned to reduce roughness [2], but subsurface porosity is created at the same time, reducing the potential influence of the former type of defect but increasing that of the latter. In this research the post-treatment route was explored to investigate and tackle the fatigue resistance issue. A representative material, laser powder bed fusion AlSi10Mg, was used. As built samples were subjected to the following post-treatments: Stress relief heat treatment (SRHT), hot isostatic pressing (HIP) and friction stir processing (FSP). The first is a thermal treatment and the other two are thermomechanical. Through tensile-tensile fatigue testing to obtain SN or Wöhler curves and fatigue crack propagation testing a thorough study of the fatigue behaviour of the material in the different states was performed. Quantitatively, in contrast with the SRHT and HIP, that showed no significant improvement, an increase of up to 100 times in fatigue life was achieved with FSP. The reason behind these differences seems to be linked mainly to the porosity reduction effect of FSP, which makes it a promising post-processing technique to improve fatigue resistance [3,4]