In Situ Observation by X-Ray Radioscopy of Liquid Decomposition During Directional Solidification of Al-Cu-Sn Alloys

Author(s)

De Albuquerque, Sarah ; Reinhart, Guillaume ; Soltani, Hadjer ; Magalhaes, Danielle Cristina Camilo ; Spinelli, Jose Eduardo ; Nguyen-Thi, Henri

• Document type: Journal article
• Source: METALS; v. 15, n. 3, p. 17-pg., 2025-03-07.

Abstract

Immiscible Al-Sn-Cu alloys may offer attractive properties, attaining superior tribological and mechanical properties when Sn-rich soft particles are homogeneously distributed in the reinforced Al-Cu matrix. In this paper, the solidifications of both Al-10 wt.% Cu-10 wt.% Sn and Al-10 wt.% Cu-20 wt.% Sn alloys were investigated to analyze the successive stages that occur during the controlled cooling of these alloys, from the initial formation of the alpha-Al dendritic array to the final eutectic reaction. In particular, we focus on the liquid-phase demixing occurring during the solidification path, which leads to the formation of Sn droplets in the melt through a nucleation-growth process. Horizontal directional solidifications were performed on thin samples in a Bridgman-type furnace, with in situ and real-time observations using X-ray radioscopy. Two different behaviors have been found concerning liquid separation: for the low-Sn-content alloy, liquid demixing occurs in one single step, whereas for the high-Sn-content alloy, it is a two-step process, with first the nucleation of a few small Sn droplets followed by a sudden formation of a large amount of wide Sn droplets. The possible causes of these different behaviors are discussed in relation to the literature, namely, either a switch from immiscible to miscible liquids or a transition from the binodal region to the spinodal region. (AU)

• FAPESP's process: 23/06107-3 - Study of the growth of AlFe primary phases in Al alloys and of intermetallic layers in Sn-Bi-X/copper joints
• Grantee: José Eduardo Spinelli
• Support Opportunities: Regular Research Grants