자동차 부품용 Al-6Si-2Cu 알루미늄합금의 미세조직 및 기계적 특성에 미치는 고용화 열처리와 Sr첨가 영향

Abstract

The effects of solution heat treatment and Sr addition in Al-6Si-2Cu for automotive parts on the microstructure and mechanical properties were investigated. The test specimens were prepared by gravity casting process. Solution heat treatments and Sr addition were applied to as-cast alloy to improve mechanical properties. The microstructure of as-cast specimens presents a typical dendrite structure, having a secondary dendrite arm spacing (SDAS) of 40 um. In addition to the Al matrix, a large amount of coarse eutectic Si, Al2Cu intermetallic phase and Fe-rich phases were identified. After solution heat treatment, single-step solution heat treatments considerably improved the spheroidization of the eutectic Si phase. Two-step solution treatments enhanced more spheroidization. The as-cast Al-6Si-2Cu alloys were well modified with Si addition and the coarse eutectic Si phases became fine. The mechanical properties of the two-step solution heat treated and Sr addition alloys showed improved mechanical properties. Consequentially, the microstructural and mechanical characteristics of the Al alloy have been successfully evaluated and are available for use with the basic data for the development of lightweight automotive parts.