Failure analysis on leakage of hydrogen storage tank for vehicles occurring in oil circulation fatigue test

In addition to the prevailing electric vehicles, the hydrogen fuel cell vehicles also attract attention for their long cruising range, quick injection speed, and low environmental pollution, etc. As the core storage equipment of high-pressure hydrogen gas in a hydrogen fuel cell vehicle, the hydrogen storage tank has to undergo a series of simulation tests for evaluation of the safety under design and special conditions before delivery. In this paper, the specimen for failure analysis is the aluminum alloy liner of the hydrogen storage tank intended for vehicles, on which cracks were formed during the oil circulation fatigue test after over 20,000 cycles. In order to find out the failure causes, optical emission spectrometer, metallographic microscope, Vickers indenter and universal testing machine were utilized to respectively inspect the chemical compositions, metallographic structure, hardness and mechanical properties of the matrix material of the tank liner, and three-dimensional stereo microscope, scanning electron microscope and energy dispersive spectrometer were employed to analyze the macroscopic and microscopic morphologies as well as the micro-area chemical compositions of the cracks. Meanwhile, the effects of fatigue crack on the liner were studied by finite element simulation. Based on these results, it was revealed that the machining marks induced from improper manufacturing and processing procedures was the root cause of the failure. Finally, the related failure mechanisms were discussed, and the pertinent countermeasures were put forward to prevent the reoccurrence of similar cases.