| AlSi10Mg is a widely used casting alloy in industry because of its characteristics of sound castability, good flowability, excellent air tightness and small hot tearing tendency. The traditional casting process cannot satisfy the requirements of fabricating Al alloy parts with complex shape and structure which is induced by lightweight. Selective laser melting(SLM) is one of the most promising method which can fabricate near net shape components from CAD model and metal powder directly. In this thesis, the process and performance of AlSi10 Mg parts fabricated by SLM were investigated. Al alloy parts with high density and good mechanical property are fabricated. The main contents and results are as follows:(1) Firstly, the process parameters of AlSi10 Mg alloy using selective laser melting were investigated. The optimized process window was obtained. It’s found that the relative density of fabricated parts decreases with the increase of scanning speed when other process parameters are fixed. In order to obtain high density samples, scanning space and layer thickness should not be too big, however, the influence of scanning space and layer thickness on relative density are not significant in a certain range. The optimal process parameters are as follows: the laser power is 200 W, the scanning speed is 50~150mm/s, the scanning space is 0.07~0.09 mm and the layer thickness is 20~40μm.(2) Secondly, the microstructure and mechanical properties of the AlSi10 Mg alloy using SLM were analyzed. Because of the high cooling rate of the SLM processing, the solid solubility of Si in Al can be extended, and a fine microstructure is formed. The crystallite size is found to be about 1μm. However, the microstructure is not uniform throughout the cross section, a fine and a coarse cellular structure inside the melt pool and a heat affected zone around the melt pool can be observed. The strengthening mechanism of SLM_ed AlSi10 Mg parts are found to be the refinement strengthening and solution strengthening. The ultimate tensile strength and yield strength are 507~518MPa and 322~331Mpa, respectively, which are about 63.4% and 94.7% higher than the casting alloy criterion. The elongation at break is 4.5%.(3) Lastly, the effects of annealing on microstructure and related mechanical properties were investigated. The microstructure of SLM_ed AlSi10 Mg changes with the annealing temperature. The Si particles dissolve from α-Al and become coarser during heat treatment. For the sample annealed at 300°C, 2h, the particle Si phase gathers and becomes acicular structure. The morphological changing of Si phase during heat treatment significantly affects the mechanical properties of the samples, The ultimate and yield strength decrease from 513 and 323 MPa for the as-built part to 367 and 242 MPa for the sample annealed at 300°C, respectively, while the elongation at break increases from 4.5 to 9.5%. Meanwhile, the microhardness decrease from 119±10HV to 88±5HV. |
