Effect of thermal annealing on microstructure evolution and mechanical behavior of an additive manufactured AlSi10Mg par
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ARTICLE Effect of thermal annealing on microstructure evolution and mechanical behavior of an additive manufactured AlSi10Mg part Pin Yang,a) Mark A. Rodriguez, Lisa A. Deibler, Bradley H. Jared, James Griego, Alice Kilgo, Amy Allen, and Daniel K. Stefan Electrical, Optical and Nano-Materials, Sandia National Laboratories, Albuquerque, New Mexico 87185, USA (Received 22 November 2017; accepted 26 March 2018)
The powder-bed laser additive manufacturing (AM) process is widely used in the fabrication of three-dimensional metallic parts with intricate structures, where kinetically controlled diffusion and microstructure ripening can be hindered by fast melting and rapid solidification. Therefore, the microstructure and physical properties of parts made by this process will be significantly different from their counterparts produced by conventional methods. This work investigates the microstructure evolution for an AM fabricated AlSi10Mg part from its nonequilibrium state toward equilibrium state. Special attention is placed on silicon dissolution, precipitate formation, collapsing of a divorced eutectic cellular structure, and microstructure ripening in the thermal annealing process. These events alter the size, morphology, length scale, and distribution of the beta silicon phase in the primary aluminum, and changes associated with elastic properties and microhardness are reported. The relationship between residual stress and silicon dissolution due to changes in lattice spacing is also investigated and discussed.
I. INTRODUCTION
The powder-bed laser melting process is one of the most popular additive manufacturing (AM) techniques in building three-dimensional (3D) metal parts. In this process, a highpower laser beam scans on a leveled thin metal powder layer in a cold or preheated powder bed. Thermal energy provided by the laser selectively melts the metallic powder, delineating and building a 2D slice pattern based on a 3D model. A complicated 3D structure can, therefore, be fabricated via this layer-by-layer approach. The approach conserves the source materials, decreases manufacturing footprint and ancillary tooling requirements, and reduces environmental impact. Furthermore, the AM process provides agility for prototyping and design of complicated parts, reduces the cost of molds for small lot production, and has a quick turn-around time for critical in-mission repair. In comparison to other castable aluminum (Al) alloys, silicon (Si)-modified alloys such as AlSi10Mg are an excellent choice for the AM process. The addition of Si lowers the melting point,1 improves weldability and fatigue performance,2 provides excellent corrosion resistance, and ductility can be modified and improved after heat treatment. If the selected composition is close to its eutectic point, there is an 83 °C degree reduction in melting point with a narrow solidification range between liquidus and eutectic a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2018.82 J. Mater. Res., Vol. 33, No. 12, Jun 28, 2
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