Change in State of Intermetallic Compounds in JIS AC4CH Aluminum Alloy during High Temperature and Short Time Solution Treatment

Abstract

  Effects of high temperature and short time solution treatment using a high-frequency induction heating apparatus on microstructure in an AC4CH aluminum alloy was investigated in terms of state changes of Mg and Si. In the as-cast condition, Mg was localized in intermetallic compounds such as Mg₂Si and π-phase (Al₈FeMg₃Si₆) with Chinese script-like and plate-like shape. The Mg₂Si phase dissolved immediately after heating to 560℃ with the heating ratio of 40℃/s. The Chinese script-like π-phase dissolved and the plate-like π-phase transformed to the β-AlFeSi phase by solution treatment at 560℃ for 3min. The amounts of Mg and Si in the primary α-aluminum phase increased significantly due to the dissolution and/or phase transformation of π-phase. It was found that the solution time necessary for the transformation of π-phase had extended in the sample containing coarse π-phase.