Investigation of the as-solidified microstructure of an Al–Mg–Si–Cu alloy

• Published in: Journal of alloys and compounds Vol. 602; pp. 312 - 321
• Main Authors: Li, Kai, Song, Min, Du, Yong, Tang, Ying, Dong, Hongbiao, Ni, Song
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 25.07.2014; Elsevier
• Subjects: AGGLOMERATION; ALUMINUM ALLOYS (50 TO 99 AL); Aluminum base alloys; BOUNDARIES; COMPUTER SIMULATION; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Grain boundaries; Liquid–solid reactions; Materials science; Metals and alloys; Microstructure; MICROSTRUCTURES; Phase diagrams and microstructures developed by solidification and solid-solid phase transformations; Physics; Scanning electron microscopy; Silicon; SOLIDIFICATION; Scanning electron microscopy; Metals and alloys; Microstructure; Liquid–solid reactions; Grain boundaries; Liquid-solid reactions; Aluminium base alloys; Volume fraction; Overageing; Precipitates; Solidification; Solution heat treatment; Transmission electron microscopy; Dendrites; Liquid solid reaction
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2014.03.026

•AlMgSiCu-Q particles preferentially grow along the solidification direction.•A new orientation relationship between Q particles and α-Al matrix was found.•The solidified microstructure was simulated based on Scheil–Gulliver model.•The effect of solidification on solution and aging processes were analyzed. The as-solidified microstructure of an Al–Mg–Si–Cu alloy was characterized by scanning electron microscopy and transmission electron microscopy. Quaternary Q particles were found to elongate preferentially along the solidification direction of the cylindrical cast ingot, whilst a small number of Si leaf-like particles aggregate mainly along the grain boundaries. The volume fractions of the Q and Si particles are quantitatively measured from electron microscopy images and thermodynamically simulated based on the Scheil–Gulliver solidification model. The results from experimental measurement agree well with those from simulation. The Q particles, which have dendrite-like internal structure and are uniformly distributed within the α-Al grains with a different orientation from that found in the aged alloys, are fast-dissolving and aid the formation of uniform aged microstructures. The aggregation of the Si particles along the grain boundaries in the as-solidified microstructure results in Si-rich boundaries even after a solution treatment, and causes the re-emergence of Si particles in the over-aged microstructure. This phenomenon helps to reduce the width of the precipitate-free zones.