Etching Method to Create Random Speckle Pattern on Semi-Solid Cast A356 Aluminium for DIC in-situ strain measurement




Aluminum semi-solid casting is constantly evolving, as it offers a combination of reduced shrinkage porosity and gas
entrapment defects together with high productivity and an extended die-life. The relationship between the microstructure
and stress-strain behavior is not well-understood due to its non-conventional microstructure. In-situ tensile testing,
combined with optical microscope and Digital Image Correlation (DIC), has been used for local strain distribution
measuements in cast irons. The critical capability was an etching technique to generate a micro-scale random speckle
pattern with a sufficiently high speckle density to enable the sufficient spatial resolution of displacement and strain.
The current paper focuses on the development of a pit etching procedure for the semi-solid cast A356 aluminum alloy to
study local strain accommodation on the microstructure during tensile loading. The critical challenge of this procedure
was the generation of homogeneously distributed pits on both the primary aluminum and eutectic regions. Therefore,
a heated solution used for wet-etch aluminum in microfabrication was modified as well as a process adapted to generate
pits with suitable characteristics. In-situ tensile tests were performed attached to an optical microscope to record
the microstructure and displacements during loading. DIC software was used for analysis. The procedure was validated
through a comparison between the resulting Young´s moduls using standard tensile testing and the DIC process
on the speckle pattern generated. A good fit between the two methods for Young´s modulus was found. The spatial resolution
obtained was, however, not sufficient to fully resolve the strain gradients in the microstructure, but it did reveal
large strain variations in the microstructure.


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Author Biography

Anders E. W. Jarfors, Jönköping University

Professor Materials and Maufacturing - Casting

Research Leader - Materials and Manufactuing


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How to Cite

Segolle, M., Santos, J., Kasvayee, K. A., & Jarfors, A. E. W. (2017). Etching Method to Create Random Speckle Pattern on Semi-Solid Cast A356 Aluminium for DIC in-situ strain measurement. Journal of Casting &Amp; Materials Engineering, 1(1), 33.