The effect of heat treatment on fatigue response of laser powder bed fused Al-Cu-Mg-Ag-TiB2 (A20X) alloy

Abstract

The paper aims at assessing the effect of heat treatment on the fatigue behavior of a novel laser-powder bed fused (L-PBF) Al-Cu-Mg-Ag-TiB2 composite, otherwise known as A20X alloy. Heat treatments, (i) stress relieving, and (ii) T7 over-aging and stabilizing, were performed on L-PBF A20X materials, followed by advanced microstructural characterizations, mechanical property measurements (utilizing tensile and depth-sensing indentation testing), and force-controlled fatigue testing. Microstructural assessments revealed the ultra-fine and fine equiaxed grain structure of the L-PBF stress-relieved and aged A20X materials. Mechanical properties (yield stress, ultimate strength, and nano-hardness quantities) of the aged material were recorded as higher than the stress-relieved counter materials. By the same token, the aged material showed better low-cycle and high-cycle fatigue performance and higher fatigue strength relative to the stress-relieved conditions. Based on detailed fractography assessments, the life-limiting fatigue failures of the studied materials (stress relived and T7 aged) were primarily governed by sub-surface L-PBF-induced volumetric defects such as pores and/or lack of fusion. The findings of this study present useful information on the role/mechanism of inevitable process-induced interior defects on fatigue behavior of the Al-Cu-Mg-Ag-TiB2 composites and the effect of post-processing (i.e., aging in this research) on fatigue behavior, which is of great significance for the high-demanding and critical applications of lightweight high-strength L-PBF Al-Cu-Mg-Ag-TiB2 composites in the space and aviation sectors.