Metallographic Investigation of Plastic Deformation for Aluminum Alloys Under Different Loading Conditions

A variety of characteristics can be extracted from analysis of a material’s microstructure. However, when it comes to evaluating the existence or extent of plastic deformation directly from the microstructure of aluminum alloys, assessment methods are often qualitative. In this study, aluminum 6061 (primary) and 7075 (supplementary) samples were loaded in tension at different loading rates to specified levels of strain, spanning from undeformed to fractured. The goal was to explore, adapt, and develop microstructure-based methods for assessing plastic deformation in a given sample. Through this process, three methods were considered: correlating (1) the statistics of the (longest) length per grain, (2) the grain density, and (3) the Knoop microhardness with the level of applied strain. For methods 1 and 2, optical microscopy was applied to as-etched samples, and these methods indicated the capacity to detect the onset of plastic deformation, whereas method 3 (microhardness) was more suitable for extent.