Assessment of Tensile Properties of Cast High Mg containing Al-Mg-Cu Aluminum Alloy with Correlation of Computed Tomography Scans and Optical Crack Surface Analysis

Abstract

In the casting of aluminum alloys, melt cleanliness has been crucial to achieve desirable final properties. Alloying elements, casting method and degassing procedures have been applied to obtain an internal structure free from defects. Most common defects have been double oxide metal films called bifilms. These defects have been detrimental to mechanical properties. Efforts in industry and academia have focused on removing those defects. Reduced pressure test (RPT) and optical evaluation of cross section of specimens have been the most preferred method of bifilm index evaluation method to assess melt quality. As this method is 2D cross-section analysis, there has not been a direct method to correlate mechanical properties with 3D volume analysis of both RPT and tensile specimens. Computed tomography scanning/imaging has been a promising and emerging method for 3D internal structure evaluation to evaluate internal defects. Subsequent mechanical properties fluctuation in correlation with defect quantity and size may be built in this methodology. In the present study, casting of aluminum alloys with high magnesium content and different alloying elements has been done. Effect of melt quality and defect quantities on internal structures have been investigated via RPT tests and computed tomography scans (CTS). Correlation of CTS and tensile tests has been shown. Tensile test specimen surfaces have been investigated via optical imaging, and bifilm effects have been shown. Alloy quality correlations with tensile tests have been established.