In situ studies of precipitate formation in Al-Pb monotectic solidification by X-ray transmission microscopy

• Published in: Metallurgical and materials transactions. A, Physical metallurgy and materials science Physical metallurgy and materials science, 1997-08, Vol.28 (8), p.1705-1710
• Main Authors: KAUKLER, W. F, ROSENBERGER, F, CURRERI, P. A
• Format: Article
• Language: English
• Subjects: Applied sciences; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Materials science; Metals. Metallurgy; Phase diagrams and microstructures developed by solidification and solid-solid phase transformations; Phase diagrams of metals and alloys; Physics
• ISSN: 1073-5623; 1543-1940
• DOI: 10.1007/s11661-997-0262-8

Al-1.5 wt.% Pb monotectic alloys were unidirectionally solidified. X-ray transmission microscope (XTM) observations, both during and after solidification, revealed various new morphological /compositional features in the melt and solid. In the melt, nonuniform lead-rich interfacial segregation layers and droplets were observed to form well ahead of the interface. In the solid, periodic striae formed at translation/solidification velocities as low as 6x10 exp -6 m/s. The striae shape does not replicate that of the interface. The striae spacing decreases from 4 to 2x10 exp -4 m with an increasing solidification rate between 6 and 16x10 exp -6 m/s. High resolution postsolidification XTM examination reveals that these striae consist of Pb-rich particles of 2 to 3x10 exp -6 m diameter. At translation/solidification velocities below 6x10 exp -6 m/s, Pb incorporation into the solid occurs in the form of continuous fibers and strings of particles of approx5x10 exp -6 m diameter. Bands, parallel to the interface, in which these fibers were aligned in the solidification direction, alternated with bands of poor fiber alignment. The width of these bands is comparable to the striae spacings obtained at the high solidification rates.