Abstract
Because of rapid solidification involved in the laser or e-beam based additive manufacturing (AM) process, solution treatable metallic parts made by these methods usually possess a unique nonequilibrium microstructure which changes significantly during subsequent thermal treatment. Such evolution alters the size, morphology, length scale, and distribution of microstructural features and has a substantial impact on thermal properties and possibly on electrical properties as well. This study focuses on effects of microstructural evolution on thermal properties of an additively manufactured AlSi10Mg part. The changes of thermal properties such as thermal expansion, heat capacity, thermal diffusivity, and thermal conductivity as a function of thermal treatment are reported. The results show that the formation of supersaturated primary α aluminum and unique cellular structure imparted by fast solidification in the AM process are the major cause for the low thermal diffusivity and low thermal conductivity observed in this solution treatable, as-built part. A correlation between microstructural evolution and changes in thermal properties is established. Advantages and tailoring of the thermal properties of additively built parts are discussed. Implications of these results are important for other additively manufactured components based on popular solution treatable alloys.
Highlights
Physical properties of solution treatable alloys strongly depend on their thermal treatment because solubility, distribution of solute atoms, and microstructure in these alloys can vary significantly
The heat capacity curve determined by the differential scanning calorimetric analysis (DSC) shows a double exothermic peak on the first heating for the asbuilt additive manufacturing (AM) part illustrated by the black solid line on Fig. 1
The results indicate that after heating to 450 °C for 15 min, the change in heat capacity with respect to temperature for the as-built sample in the second run is close to that of pure aluminum and the heat capacity value approaches to the classical value of 3R [R: gas constant or Cp ; 0.924 J/J/ (g °C)]
Summary
Physical properties of solution treatable alloys strongly depend on their thermal treatment because solubility, distribution of solute atoms, and microstructure in these alloys can vary significantly. Hardness, and toughness can be tailored by solution strengthening, precipitation hardening, and microstructural ripening with proper thermal treatments for specific applications.[1,2,3] Some of these alloys, such as Ti6Al4V, Inconel 718, and AlSi10Mg, are popular in laser- or electron beam-4 based additive manufacturing (AM). When these powders are subjected to fast melting and rapid solidification in the AM process, a quenched, nonequilibrium microstructure is developed. The AlSi10Mg alloy offers a low melting point,[5] good weldability, and improved mechanical properties after proper thermal treatment.[1,2,3] This specific composition is located at the hypoeutectic region of the Al–Si phase diagram close to its eutectic point; it has a narrow solidification range between its liquidus and eutectic temperatures6—permitting a tighter dimensional control for building complex shapes and overhang structures
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