Microstructure and properties of selective laser melting AlSi7MgTi alloy

Abstract

The testing blocks of AlSi7MgTi alloy were prepared by selective laser melting (SLM) technique and T6 heat treatment using alloy powders fabricated by supersonic gas atomization equipment. The microstructure, phase composition, residual stress, and mechanical properties of as-built and T6 treated alloys were investigated by optical microscope,scanning electron microscope,X-ray diffractometer,Raman spectrometer and tensile tests, respectively. The results indicate that as-built alloy mainly consists of supersaturated α(Al) solid solution and Si phases. The microstructure characterized by layer-by-layer stacking and interlaced of "scale-like" melt pool, shows obvious anisotropy. In addition, Si phase exists in the form of cellular eutectic silicon, which is connected by blocky and fibrous eutectic silicon. The eutectic silicon near melt pool boundary is relatively thick, while it is smaller in interior of melt pool. T6 heat treatment promotes the precipitation of Si phases, and leads to the Ostwald coarsening of eutectic silicon. Meanwhile, the melt pool morphologies and cellular eutectic silicon structure are basically eliminated by T6 heat treatment. Additionally, the residual stress is significantly reduced after heat treatment. The tensile strength and yield strength of as-built alloy reach up to 420-430 MPa and 280-300 MPa respectively, with elongation of 5.1%-11.0%. However, the tensile strength of T6 heat treated alloy is reduced to about 360 MPa, and yield strength is almost equal to that of as-built alloy, while elongation increases to 15.2%-16.5%.

Keywords

• selective laser melting
• alsi7mgti alloy
• t6 heat treatment
• microstructure
• mechanical property