Microstructural Evolutions and Strengthening Mechanism according to the Aging Temperatures of a High Si Cast Aluminum Alloy

A356 cast aluminum alloy contains 7 at.% Si and 0.3 at.% Mg, producing an approximately 50% eutectic microstructure. This high Si content and various casting conditions play a significant role in strengthening A356 alloy, by controlling the eutectic morphology and precipitates of other intermetallic compounds. Understanding how Si-related precipitates and clusters are soluble in the α-matrix is necessary to provide high strength and fatigue resistance to A356 alloys. The aging heat-treatment temperature in the A356 alloy most likely promotes the formation of these precipitates and clusters. The A356 samples were differently aged at temperatures of 110 oC and 130 oC for 2 h, and were labeled 110A, and 130A, respectively. 110A was found to have improved mechanical properties, such as high strength and elongation, compared to 130A, which may be attributed to the formation of secondary phases in the α-phase matrix. Scanning and transmission electron microscopy and atom probe tomography analyses demonstrated Ti2Si precipitation and various-sized cluster formations in 110A. In contrast, 130A had fewer clusters than 110A. Therefore, different aging heat-treatment temperatures relate to a change in the behavior of atoms, affecting the mechanical properties.