Neutron Imaging of Al6061 Prepared by Solid-State Friction Stir Additive Manufacturing

Abstract

Solid-state Friction Stir Additive Manufacturing has recently gained attention as a result of its capacity to fabricate large-scale parts while preserving the mechanical properties of the feedstock material. However, the correlation between the quality of layer-by-layer bonding of the deposited metal and processing parameters has remained unknown. Neutron imaging techniques, with 90% total transmission per cm, are employed for Al6061 parts fabricated by MELD® Technology as a non-destructive evaluation approach for the first time to investigate the layer-by-layer structure of a stadium-shaped ingot in different sections. The post-processed results show the fabricated parts with an optimized set of processing parameters are void-free. However, the hydrocarbon-based feedstock lubricant segregates between the layers, which consequently may lead to non-uniform weaker mechanical properties along the build direction and stimulate crack initiation during mechanical loading. The tensile test results show 14% lower strain-to-failure values in alleged contaminated areas in transmission imaging results. Additionally, layer bonding is significantly impacted by hot-on-hot and hot-on-cold layer deposition schemes, especially for larger layer thicknesses.

The Effects of Layer Thickness on the Mechanical Properties of Additive Friction Stir Deposition-Fabricated Aluminum Alloy 6061 Parts

“…For AFSD, the layer boundaries are formed differently from a regular layer-by-layer printing because of re-stringing of the previous layer [29,31]. Saber et al investigated the layer-by-layer architecture of distinct segments within as-built AA6061 parts created via the AFSD process, employing neutron imaging techniques as a non-destructive evaluation methodology [30]. Their observations indicated that the graphite coating, employed as a dry lubricant on the feedstock's surface, exhibited a tendency to segregate between layers.…”

“…Aluminum alloys, known for their lightweight nature, possess exceptional strength-to-weight ratios, as well as remarkable resistance to corrosion [28]. Notably, the literature has documented the successful utilization of AFSD in the manufacturing of AA6061 [19,29,30], AA2050 [31], AA2011 [32], AA2024 [13], AA2219 [33,34], AA5083 [35,36], AA5B70 [37], and AA7075 [24,[38][39][40][41] parts, showcasing the versatility and potential of this technique for aluminum alloy processing. The deposition of parts made of other metal alloys is also reported in the literature.…”

“…Merritt et al integrated thermocouples into the deposition tool to enable real-time temperature monitoring [53]. Nemati et al used neutron imaging to investigate the layer-by-layer structure of an AFSD as-deposited AA6061 part [30]. Numerous efforts to simulate the AFSD process have also been documented [54][55][56][57].…”