Multiaxial deformation behavior of aluminum alloy 6061 subjected to fire damage

Abstract

Aluminum alloy AA6061 is of interest to the US Navy for ship structure applications due to its light weight, ease of manufacturing, corrosion resistance and strength. However, response to complex loading subsequent to fire damage presents a concern for practical applications. The purpose of this study is to evaluate the effect of fire damage on the microstructure and material response of AA6061 with applied tensile, torsional, and combined loading. Fire exposure was simulated in a controlled environment and testing under multi-axial loading conditions was carried out on virgin and fire damaged samples to evaluate mechanical response. Because of the non-circular sample cross-section, a three-dimensional digital image correlation technique was used to capture the evolution of local strains over the gage length of a deforming specimen subjected to tensile and/or torsional loading. Additionally, microstructure was investigated by electron backscatter diffraction at target cross-section locations subsequent to fire exposure and/or mechanical testing. Results indicate a 60–70% strength reduction with fire exposure. Fire exposed samples achieved higher maximum tensile load during combined loading compared to pure tensile loading. Microstructure was relieved by fire exposure while mechanical loading reveals strain-induced grain refinement. With sample geometry leading to stress concentrations, a deviation from yield values predicted by conventional yield criteria was observed; multi-axial stress-strain data can be of help in assessing the state of aluminum alloy structures after fire exposure.