Effect of high-pressure heat treatment and aging on mechanical properties and very high cycle fatigue behavior of PBF-LB AlSi7Mg

This study investigates the influence of an innovative high-pressure heat treatment (HPHTTM), a single-step process that integrates hot isostatic pressing and heat treatment, on the microstructure, mechanical response, and very-high-cycle fatigue (VHCF) behavior of powder bed fused–laser beam (PBF-LB) AlSi7Mg alloy. A comprehensive set of characterization and testing, including advanced electron microscopy, high-resolution micro-CT, uniaxial tensile testing, and ultrasonic fatigue testing, was employed to establish quantitative correlations among defect population, microstructural evolution, mechanical properties, and fatigue resistance. Fractographic analysis using optical and scanning electron microscopy enabled detailed identification of crackinitiation modes across the examined fatigue regime. The HPHTTM process produced a marked transformation of the PBF-LB microstructure, including dissolution of the characteristic Al–Si cellular network and the formation of a refined distribution of nanoscale precipitates in the aged condition. Stress amplitude–life data revealed fatigue strengths at 109 cycles of 479.8 MPa, 231.0 MPa, and 225.1 MPa for the as-built, HPHTTM + aged, and HPHTTM conditions, respectively. These results collectively highlight the competing roles of defect mitigation, microstructural homogenization, and precipitation hardening in governing the long-life fatigue behavior of additively manufactured AlSi7Mg, and they demonstrate the potential of HPHTTM as a process route for tailoring the balance between strength, ductility, and VHCF performance