Seminar - Carlos Caceres - Grain Size Hardening in Mg and Mg-Zn Solid Solutions

Tuesday 24 November 2009, 2.00 pm - 3.00 pm
Civil Engineering Lecture Theatre 3

Grain Size Hardening in Mg and Mg-Zn Solid Solutions
A/Prof Carlos Caceres
Casting Technology Materials Engineering at UQ

Abstract:
Random polycrystals of pure Mg and Mg-Zn binary alloys with up to 2.3 at.%Zn with a wide range of grain sizes have been deformed in tension and compression. The k-values calculated from Hall-Petch plots of the 0.2% proof stress increased with the Zn content, from about 0.24 MPa m1/2 for pure Mg to ~0.66 MPa m1/2 for the 2.3 at.%Zn alloy. The k-values were larger in compression than in tension. When the strength measurements were corrected for the pseudoelastic strain resulting from elastic twinning, the k-values increased, to 0.28 MPa m1/2 for pure Mg and ~0.7 MPa m1/2 for the 2.3 at.%Zn alloy. The difference in k-values between tension and compression was substantially reduced by the correction for pseudoelasticity, suggesting that the larger values observed in compression are an artefact created by elastic twinning. The friction stress varied between about 14 MPa for the pure Mg to very low or negative values for the more dilute alloy, increasing again to about 8 MPa for the concentrated alloys. Possible reasons for the increase in k-value and the minimum in friction stress as the solute content increased are discussed in terms of solid solution hardening and softening effects.

Presenter Biography
Dr Carlos H. Cáceres
Reader in Casting Technology
School of Engineering
The University of Queensland
Brisbane Australia

Carlos Cáceres earned a PhD in Physics from the University of Cordoba, Argentina, in 1980. He subsequently was a Research Associate at McMaster University, Hamilton, Canada. Since 1991 he has been with the School of Engineering, The University of Queensland.

He has been Visiting Professor at the University of Windsor (Ontario), the University of British Columbia (Vancouver), Charles University (Prague), the Icelandic Institute of Technology (Reykjavik), IIT Bangalore, South China University of Technology (Guangzhou).

At UQ he teaches Physical Metallurgy and Materials Selection in Mechanical Design. His research interests have covered acoustic emission, phase transformations, superplasticity, creep and creep fracture of metals and ceramics, processing of ceramic powders, etc.

In recent years his research has concentrated on the micromechanics of deformation and fracture of aluminium and magnesium casting alloys, and on environmental issues regarding light alloy applications.

He is currently a CI within the CRC-CAST and the Centre of Excellence Design in Light Metals. He has published over 120 technical papers in journals and conference proceedings.

c.caceres@uq.edu.au
http://www.uq.edu.au/~e5ccacer/