Al-5.2Si-3.4Cu-0.28Mg 합금의 미세조직 및 기계적 특성에 미치는 용체화 및 시효 열처리의 영향

Since strength and ductility have a trade-off relationship in Al alloys, controlling these properties using heat treatments requires careful attention to the dissolution and evolution of the reinforcing phases. In this study, the effects of solution and aging treatments on the microstructure and mechanical properties of Al-5.2Si-3.4Cu-0.28Mg alloy were investigated. 1-step and 2-step solution treatments were conducted at 495 and 520 ℃ with various holding times, which were determined by thermal analysis. At 495 ℃, the eutectic θ(Al2Cu) phases were quickly dissolved while block-shaped θ phases remained, even until 13 hours. During the 2-step treatment at 520 ℃, these remaining phases were melted both in the grains and boundaries. Although all of the Q(Al5Cu2Mg8Si6) phases were completely dissolved in the 2-step treatment, the hardness of the 2-step treated specimen was lower than the 1-step treated one. After solution treatments at 495 ℃/9 hours, where the highest hardness was observed, artificial aging treatments were conducted at 160 and 200 ℃ with various times. Yield and ultimate tensile strengths showed similar values at the peak aging regardless of the temperature, while higher hardness (117%) and elongation (281%) were obtained at 160 than 200 ℃. Based on the observed results, the correlations between the microstructures and mechanical properties by the heat treatments were investigated. (Received July 5, 2017; Accepted September 18, 2017)