Thermo-mechanical and metallurgical aspects in friction stir processing of AZ31 Mg alloy - A numerical and experimental investigation

A. N. Albakri, Bilal Mansoor, H. Nassar, Marwan Khraisheh

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42 Citations (Scopus)

Abstract

Friction stir processing of AZ31 Mg alloy was investigated by numerical modeling and experiments. A CFD based, fully coupled, 3D, thermo-mechanical model was built to better understand the effect of process parameters on temperature, material flow and strain rate. In order to account for material softening phenomena at elevated temperatures and extremely high strain rates that occur during the FSP process, experimentally measured peak temperatures were utilized to introduce a correction function in the flow stress constitutive relation. The numerical results showed that rotational speed as compared to translational speed had a more dominant effect on temperature field and strain rate. In addition, the asymmetric material flow around the tool axis caused higher peak temperature and strain rate on the advancing side (AS), while the material in the path of tool pin was swept around the retreating side (RS). FSP experiments confirmed peak temperatures measured at sheet surface near shoulder perimeter on AS were always higher than corresponding RS peak temperatures, under the selected range of process parameters. In addition to thermo-mechanical aspects, the metallurgical characteristics of FSP i.e. mainly the grain size evolution was studied by optical and electron microscopy. Experiments revealed that the coarse bimodal microstructure of as-received AZ31 Mg was subdivided into a defect-free, fine grain microstructure at the rotational speed of 1000 rpm, while a defect-free but a relatively coarse and bimodal microstructure evolved in the material at rotational speeds higher than 1000 rpm. Furthermore, in the selected range of process parameters the increases in translational speed resulted in finer grain sizes without the formation of voids or defects.

Original languageEnglish
Pages (from-to)279-290
Number of pages12
JournalJournal of Materials Processing Technology
Volume213
Issue number2
DOIs
Publication statusPublished - 1 Feb 2013
Externally publishedYes

Fingerprint

Numerical Investigation
Experimental Investigation
Friction
Strain rate
Strain Rate
Process Parameters
Processing
Microstructure
Defects
Bimodal
Grain Size
Temperature
High Strain Rate
Flow Stress
Experiments
Electron Microscopy
Softening
Constitutive Relations
Perimeter
Voids

Keywords

  • AZ31
  • CFD
  • Friction stir processing
  • Grain refinement
  • Mg
  • Microstructure

ASJC Scopus subject areas

  • Computer Science Applications
  • Modelling and Simulation
  • Ceramics and Composites
  • Metals and Alloys
  • Industrial and Manufacturing Engineering

Cite this

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abstract = "Friction stir processing of AZ31 Mg alloy was investigated by numerical modeling and experiments. A CFD based, fully coupled, 3D, thermo-mechanical model was built to better understand the effect of process parameters on temperature, material flow and strain rate. In order to account for material softening phenomena at elevated temperatures and extremely high strain rates that occur during the FSP process, experimentally measured peak temperatures were utilized to introduce a correction function in the flow stress constitutive relation. The numerical results showed that rotational speed as compared to translational speed had a more dominant effect on temperature field and strain rate. In addition, the asymmetric material flow around the tool axis caused higher peak temperature and strain rate on the advancing side (AS), while the material in the path of tool pin was swept around the retreating side (RS). FSP experiments confirmed peak temperatures measured at sheet surface near shoulder perimeter on AS were always higher than corresponding RS peak temperatures, under the selected range of process parameters. In addition to thermo-mechanical aspects, the metallurgical characteristics of FSP i.e. mainly the grain size evolution was studied by optical and electron microscopy. Experiments revealed that the coarse bimodal microstructure of as-received AZ31 Mg was subdivided into a defect-free, fine grain microstructure at the rotational speed of 1000 rpm, while a defect-free but a relatively coarse and bimodal microstructure evolved in the material at rotational speeds higher than 1000 rpm. Furthermore, in the selected range of process parameters the increases in translational speed resulted in finer grain sizes without the formation of voids or defects.",
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