Process-Dependent Composition, Microstructure, and Printability of Al-Zn-Mg and Al-Zn-Mg-Sc-Zr Alloys Manufactured by La
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VE manufacturing (AM) is emerging as an innovative technology to fabricate net-shape metal components through layer by layer process, as opposed to conventional subtractive manufacturing. Among the
LE ZHOU, HOLDEN HYER, and YONGHO SOHN are with Advanced Materials Processing and Analysis Center, Department of Materials Science and Engineering, University of Central Florida, Orlando, FL 32816. Contact e-mail: [email protected] SAKET THAPLIYAL and RAJIV S. MISHRA are with Center for Friction Stir Processing, Department of Materials Science and Engineering, Advanced Materials and Manufacturing Processes Institute, University of North Texas, Denton, TX 76207; BRANDON MCWILLIAMS and KYU CHO are with Weapons and Materials Research Directorate, CCDC Army Research Laboratory, Aberdeen Proving Ground, MD 21005. Manuscript submitted December 11, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS A
many technologies within AM, powder bed fusion (PBF) method, e.g., laser powder bed fusion (LPBF), has gained extensive industrial interests. The process involves repeated melting and solidification of several powder layers by a fast-moving laser source. LPBF has a cooling rate of the order of 104 to 107 K/s,[1] although the thermal exposure of a location depends on subsequent-and-repeated laser scans. This process can produce solidification microstructure and/or properties different from those alloys manufactured by conventional routes. The characteristics of the LPBF technology also bring challenges to many materials, especially for Aluminum alloys (AA’s). The Al-Si eutectic-based alloys have been proven highly favorable for LPBF due to their good castability, and therefore a subject of many investigations.[1–4] Several researchers have attempted to additively manufacture wrought and/or age-hardenable AA’s, such as high strength 2xxx,[5] 6xxx[6] and 7xxx[7–9] alloys and corrosion-resistant 5xxx[10,11] alloys.
However, their results demonstrated that these alloys suffered from defects such as porosity or solidification cracks over a wide range of processing parameters. Therefore, there is a strong motivation to improve the printability of AA’s. Two different approaches have been reported to solve the challenges associated with solidification cracking observed in LPBF of AA’s. One is to augment and identify the proper LPBF parameters. Uddin et al.[12] recently reported that, by heating the powder bed to 500 °C, AA6061 alloy can be manufactured without formation of solidification. Similarly, Raffeis et al.[13] successfully manufactured crack-free AA2099 alloy with a pre-heat temperature of 520 °C. The high temperature of pre-heated powder bed was postulated to lower the thermal gradient and cooling rate during the solidification, thereby reducing or eliminating the solidification cracks. However, a high temperature was used for the build plate in both cases, which requires stricter control of the LPBF environment, and can also affect the final mechanical property of the as-built component. Furthermore, the component can undergo different in-situ heat
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