Development of a Cast Al-Mg2Si-Si In Situ Composite: Microstructure, Heat Treatment, and Mechanical Properties

An Al-11Mg2Si-Si in situ composite was prepared by a modified investment casting technique that employs sub-pressure for castability improvement and immersion of ceramic shell molds in fluidized beds of silica sand and iron particles for heat extraction improvement. The microstructure of the as-cast composite is explained according to the pseudoeutectic Al-Mg2Si phase diagram. The positive effect of a decreased number of mold investment layers and cooling assisted by immersion of the mold in a metallic bed on the tensile strength and hardness of the heat treated composite is noted. A minor presence of Fe in the master alloys constitutes an essential factor for the brittleness of the composite. Solution treatment notably improves the tensile strength of the composite; however, prolonged treatment deteriorates its ductility. The effect of time and temperature of the aging treatment on the hardness of the composite is investigated. The positive influence of cooling assisted by a metallic fluidized bed on the effectiveness of the aging treatment is noticed.