Microstructure, tensile strength, and hardness of AA5024 modified with ZrH4 additions produced by laser powder bed fusion

Abstract

This work investigates the effect of ZrH4 additions on a commercial AA5024 aluminum alloy produced via Laser Powder Bed Fusion (L-PBF) where pre-mixed powders of AA5024 and ZrH4 were used. The microstructure was characterized using light and scanning electron microscopy assisted by energy-dispersive X-ray spectroscopy, and electron backscattered diffraction. The mechanical properties were evaluated by hardness and tensile measurements. The ZrH4 additions modify the microstructure. Regions without particles originate the large and elongated grains, while regions with undissolved ZrH4 or formed particles during solidification originate a fine equiaxed microstructure. The fine-grained region is typically located at the boundary of the melt pools, while the coarse-grained region is formed within the melt pools. There is substantial grain refinement with additions higher than 2.0 wt% ZrH4, nearly eliminating the coarse-grained region. The grain size does not differ in the fine-grained region for the different ZrH4, cross-sections (perpendicular or along the printing direction), or printing parameters. The 〈110〉 crystallographic fiber texture is identified, and a few particular texture components are more pronounced, such as the Cube {001} 〈100〉, the rotated Cube {001} 〈110〉, the Goss {011} 〈001〉, and Z {111} < 110>. Low texture index values are obtained in the fine-grained region, indicating the highly isotropic microstructure. The hardness and tensile strength increase with the increase in ZrH4 content for the as-built condition. A saturation in tensile strength is reached after 1.0 wt% ZrH4 additions.