Powder Bed Fusion 공정을 이용한 AlSi10Mg 합금의 제조, 미세조직 및 기계적 특성

초록

The fabrication, microstructure and mechanical properties (tensile, fatigue, wear etc.) of AlSi10Mg alloy manufactured via selective laser melting process were investigated. The effect of post heat treatment (as-built, T6, DA) on microstructure and mechanical properties was also examined. Direct aging (DA) process without solution heat treatment was employed as a post heat treatment to prepare specimens. Specimens were also arranged via the conventional solution heat treatment + precipitate hardening (T6) for comparison. Initial microstructure observation results revealed that the as-built alloy showed the unique characteristic of SLM material’ microstructure having cellular structure together with molten pool. The cellular structure boundaries were found to contain eutectic Si and a small amount of nano size Si particles inside the cellular structure. After the solid solution + T6 heat treatment, the unique microstructural characteristic of the SLM as-built material disappeared, whereas the Si particles became as coarse as several μm. On the other hand, the DA heat treated alloy, even after the heat treatment, maintained the molten pool and cellular structure and contained a lot of Si precipitates (nano size) inside the cellular structure. Room temperature tensile results showed that the DA alloy possessed superior tensile strength compared with the as-built and T6 alloys. The elongation of the DA alloy was 6.2%, which was about 3% lower than that of the as-built alloy. The fatigue properties were influenced by the morphology and size of the Si particles, both controlled by adjusting the heat treatment. The alloy that was processed using DA heat treatment had superior fatigue properties due to its cellular structural morphology characterized by a significant amount of fine Si precipitates. Compared with the as-built and T6 specimens, the superior fatigue limit of the DA alloy is attributable to its outstanding strength characteristics.