Production of in-Situ Al–Si functionally graded materials (FGMs) from A390 alloy

Abstract

Although hypereutectic A390 (Al–Si–Cu) alloys are widely used in engine liners due to their superior wear resistance, conventional casting methods fail to provide the functional gradient required by internal combustion engines – specifically, high hardness at the inner surface and toughness at the outer surface – in a single processing step. The aim of this study is to produce in-situ formed Functionally Graded Materials (FGMs) from A390 alloy by optimizing centrifugal casting parameters and to elucidate the underlying microstructural segregation mechanisms. In this study, the effects of casting temperature (700 °C and 750 °C) and mold rotational speed (1,000, 1,250, and 1,500 rpm) on radial solidification behavior and phase distribution were systematically investigated. The selected range of rotational speeds was intended to establish a balance between the centrifugal force required to segregate Si particles and the structural disturbances induced by excessive turbulence. Microstructural characterization was carried out using SEM and EDS analyses, while mechanical properties were evaluated by Brinell hardness measurements taken along the radial cross-section. Results showed that the casting parameters play a critical role in governing the migration behavior of primary Si particles. The highest inner-surface hardness (92 HB) was achieved at a casting temperature of 700 °C and a rotational speed of 1,000 rpm. At higher rotational speeds, such as 1,500 rpm, increased turbulence and vibration effects were found to reduce segregation efficiency, leading to a decrease in hardness values (88 HB). The lower casting temperature of 700 °C increased the solidification rate, thereby suppressing the growth of Si particles leading to a grain refinement. The results also showed that, by optimally controlling the centrifugal casting parameters, a functionally graded (FG) structure was achieved in the A390 alloy, which can potentially be used in the manufacturing of monolithic engine liners without the need for any additional joining process.