Aluminum clad materials that consist of a brazing sheet, a core liner and a water liner are conventionally applied to the tube material for automotive heat exchangers, where down-gauging of the components has been continuing in recent years. Coarse Si particles which can be formed in the casting process of hypo-eutectic Al–Si brazing sheet occasionally cause a melt-through of the tube alloy during the brazing process. Addition of Sr as a minor element to the brazing alloy is well known as one of the microstructural modification methods to reduce the size of Si particles. However, the crystallographic effect of Sr on Si particle growth has not been clarified yet. In this study, a crystal structural analysis for Al–12 mass%Si alloys with and without Sr-addition was performed and in the alloy with Sr-addition, a formation of hexagonal Al₂Si₂Sr with P has been identified. The formation of Al₂Si₂Sr indicates the suppression of the growth of Si particles under a specific combination of P content and Sr content because the formation temperature of Al₂Si₂Sr is thermodynamically estimated to be higher than that of AlP, which works as a nucleus of the growth of Si crystal, and Al₂Si₂Sr is incoherent with Si.

The wear behavior of Al–Si alloys against a Carbon Fiber Reinforced Plastic was investigated under the lubricated condition. In an initial wear stage, primary Si particles were exposed from the aluminum matrix, and carbon fibers were exposed from the plastic matrix. Exposure of Si particles and carbon fibers was observed also in a mild wear stage. New hyper-eutectic aluminum alloy which doesn’t contain coarser Si particles provides better wear resistance and less hostility to CFRP, compared to conventional Al–Si system alloys.