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Title: Characterisation and modelling of defect formation in direct-chill cast AZ80 alloy

Wrought magnesium alloys for demanding structural applications require high quality defect free cast feedstock. The aim of this study was to first identify and characterise typical defects in direct chill cast magnesium–aluminium–zinc (AZ) alloy billet and then use modelling to understand the origins of these defects so they can be prevented. Defects were first located using ultrasonic inspection and were then characterised using X-ray computed tomography (XCT) and serial sectioning, establishing the presence of oxide films and intermetallic particles Al{sub 8}Mn{sub 5} in all defects. A model was developed to predict the flow patterns and growth kinetics of the intermetallic phases during casting, which influence the formation of defects. Simulation of the growth of the intermetallic particles demonstrated that precipitation from the liquid occurs in the mould. The combination of the entrained oxide films and intermetallic particles recirculates in the liquid metal and continues to grow, until large enough to settle, which is predicted to occur at the centre of the mould where the flow is the slowest. Based on these predictions, strategies to reduce the susceptibility to defect formation are suggested. - Highlights: • Casting defects in magnesium direct chill casting have been imaged and characterised in 3-dimensions. •more » The occurrences of co-located clusters of particles and oxide films have been characterised and explained. • A coupled model has been developed to help interpret the observed trend for defects located towards the centre of billets.« less
Authors:
; ;  [1] ;  [2]
  1. School of Materials, University of Manchester, Manchester M13 9PL (United Kingdom)
  2. Magnesium Elektron UK, Rake Lane, Manchester, M27 8BF (United Kingdom)
Publication Date:
OSTI Identifier:
22476102
Resource Type:
Journal Article
Resource Relation:
Journal Name: Materials Characterization; Journal Volume: 104; Other Information: Copyright (c) 2015 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ALUMINIUM; ALUMINIUM COMPOUNDS; CASTING; COMPUTERIZED TOMOGRAPHY; DEFECTS; FILMS; INSPECTION; INTERMETALLIC COMPOUNDS; LIQUID METALS; MAGNESIUM ALLOYS; OXIDES; PRECIPITATION; X RADIATION; ZINC ALLOYS