TANG Pengjun, CHEN Bingqing, YAN Taiqi, CHU Ruikun, GUO Shaoqing, LI Peiyong
Residual stress, always existing in additive manufactured AlSi10Mg alloy, has negative effects on its application. Therefore, it is needed to be controlled or even eliminated by heat treatment. The microstructure, properties and residual stress of as built and annealed alloys are investigated using X ray diffraction, optical microscope, field emission scanning electron microscope, transmission electron microscope, electron backscattered diffraction, microhardness and Raman spectrum tests. The results show that as built alloy consists of supersaturated Al solid solution and Si phase. Additionally, the Si phase exists in the forms of cellular eutectic silicon and dispersed silicon nanoparticles. Meanwhile, the grain size of as built alloy is relatively fine, and the d50 value of grain size distribution is about 10.4 μm. Annealing treatments lead to the depositions of alloying elements from supersaturated Al solid solution, and formations of equilibrium phase Mg2Si and Si phase as the annealing temperature ranging from 250℃ to 300℃. With the increase of annealing temperature, the alloying elements precipitate out more thoroughly. Furthermore, the coarsening of cellular eutectic silicon and silicon nanoparticles, grain growth and recrystallization also occur owing to annealing treatment. Because of the decline of fine grain strengthening, solid solution strengthening and dispersion strengthening after annealing treatment, the microhardness decreases. The residual stress, however, can be significantly reduced by annealing process with a reduction of 60%~80%. Consequently, it is necessary to develop new heat treatment system according to the characteristic of additive manufactured aluminum alloy, in order to regulate and control the microstructure and properties.
