Characteristics And Performance Of Selective Laser Melting Al-Si Alloy

There is a great demand for complex shaped thin-walled aluminium alloy parts in modern aerospace equipment. Al-Si alloy has widely been used in modern aerospace industry production for its good fluidity, wear resistance, erosion resistance and low thermal expansion coefficient. However the conventional fabrication technologyies can't be able to fabricate complex shaped thin-walled Al-Si alloy parts. Selective laser melting(SLM) is a potential technique to manufacture thin-walled Al-Si alloy parts with complex shape. This thesis studied the forming characteristics and performance of Al-Si alloy by selective laser melting. Relationships between process parameters and forming characteristics such as relative density, microstructure and defects were obtained. It also revealed the relationships between process parameters and the performances of surface roughness, micro hardness and tensile property at room temperature. The samples with average relative density above 99.8 %, tensile strength above 505 MPa and elongation above 3.8% were fabricated. The main research contains and results are shown as below:(1)Firstly, this thesis studied the relationships between process parameters and forming characteristics such as relative density, microstructure and defects and process window. It also analyzed the categories and forming mechanism of defects in the process and some preventive methods were proposed. The results show that when the laser power is high or the layer thickness is small, the relative density increases first and then decreases with the increase of scanning speed. But when the laser power is low or the layer thickness is large, the relative density decreases with the increase of the scanning speed. The microstructure of the samples includes ?-Al phase and Si phase,Si connects to form plates surrounding the ?-Al phase. The main defects are holes and cracks. Holes includes pores and auxiliary holes which could be eliminated by using appropriate process parameters. Cracks cause by large flaky Si phase could be controlled by optimizing process parameters and reducing the forming height.(2)Secondly,the thesis investigated the relationships between process parameters and performance of surface roughness and micro hardness. Results show that surface roughness increases with scanning speed while micro hardness has little to do with scanning speed and shows no obvious anisotropy. The surface roughness and micro hardness of samples are 13~18 ?m and 149~153 Hv can be obtained by using optimal process parameters.(3)Lastly, crack-free samples were fabricated by using the optimum process parameters. The average relative density is above 99.8 %, the as-deposited average tensile strength, yield strength, elastic modulus and elongation are 505 MPa, 326 MPa, 75.2 GPa and 3.8%, respectively.