热处理对增材制造AlSi10Mg合金组织性能及残余应力的影响

 增材制造AlSi10Mg合金通常存在较大的残余应力，对材料的服役使用产生不利影响，故需要采用热处理对残余应力予以控制甚至消除。利用X射线衍射、光学显微镜、场发射扫描电子显微镜、透射电子显微镜、背散射电子衍射、维氏硬度和拉曼光谱试验，研究了成形态和退火态合金的显微组织、性能及残余应力。结果表明，成形态合金由过饱和Al固溶体和Si相组成，其中， Si相以网状共晶硅和弥散分布的纳米硅颗粒2种形态存在。同时，成形态合金的晶粒细小，其晶粒尺寸分布的d₅₀值约为10.4 μm。250~300℃退火使合金元素从过饱和Al固溶体中析出，形成平衡相Mg₂Si和Si相；且随着退火温度升高，合金元素析出越彻底。此外，退火还引起网状共晶硅和纳米硅颗粒粗化，促使晶粒长大并诱发再结晶。由于退火后合金中的细晶强化、固溶强化和弥散强化效果减弱，故合金的维氏硬度下降。然而，退火可以显著降低合金的残余应力，下降幅度达到60%~80%。因此，为更好地实现组织和性能调控，有必要针对增材制造铝合金的特点开发新的热处理制度。

Effects of heat treatment on microstructure,properties,and residual stress of additive manufactured AlSi10Mg alloy

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.