Improved understanding of environment-induced cracking (EIC) of 5xxx and 7xxx series aluminum alloys
N J Henry Holroyd 1,2, Timothy L Burnett 1 and John J Lewandowski 2
1 Henry Mosely X-ray Imaging Facility, School of Materials, The University of Manchester, Manchester, UK
2 Department of Materials Science & Engineering, Case Western Reserve University, Cleveland, Ohio, USA
Two recent experimental findings will be presented: a) direct observations of environment-induced crack (EIC) initiation and the early stages of crack growth for 5xxx (Al-Mg) and 7xxx (Al-Zn-Mg-Cu) series aluminum alloys exposed to various environments, achieved employing 3D computed tomography, while subjecting smooth tensile test specimens to slowly increasing strain and b) a novel use of load-time behavior from the conventional slow strain rate (SSRT) testing of smooth tensile test specimens that enables an estimation of EIC crack velocity (cv) - stress intensity factor (K) behaviour promoted during testing.
3D computed tomography data has been correlated to the mechanical test data so that the emerging cracks are clearly in context of the driving forces applied. Several significant insights have been revealed with this approach: the location of initiation sites, the quantified location, morphology and dimensions of the developing cracks, and when coupled with the time-lapse observations, the kinetics of the different stages of cracking. From this we aim to characterize the details pertinent to EIC initiation, the transition to cracking and the growth of microstructurally short and long cracks. This is within statistical context of being able to watch 10’s of cracks emerge in the typical colonies associated with this failure mechanism.