Effect of electrochemical hydrogen charging on the microstructure and mechanical behavior of a duplex structured Mg-8wt.%Li alloy

In this work, through performing microstructural characterization, tensile testing and failure analysis, the influence of electrochemical hydrogen charging on the microstructure and mechanical behavior of an as-cast Mg-8wt.%Li alloy was investigated. It revealed that after being hydrogen charged at 50 mA/cm² for respectively 3 h, 6 h and 18 h in 0.1 M NaCl solution, obvious HID occurred and the damage degree was gradually increased with the hydrogen charging time. For the sample being hydrogen charged for 3 h, micro pores with the diameter ranging from 10 ~ 30 µm were formed and preferentially present in α-Mg phase. Moreover, micro cracks with the length ranging from 10 ~ 50 µm mainly initiated in α-Mg phase, at α-Mg/β-Li interfaces and the peripheries of pores. With the increase of hydrogen charging time, the numbers of pores and cracks were obviously increased. Tensile results revealed that the hydrogen charging can simultaneously decrease the tensile strength and ductility of the alloy. Compared with the uncharged sample, the tensile yield strength, ultimate tensile strength and the elongation ratio to failure were respectively reduced by 5.7%, 7.3%, 31.7% for the 3h-charged sample and 24.6%, 24.8%, 67.0% for the 18h-charged sample. Failure analysis indicated that hydrogen charging can induce the brittle cracking of the alloy and the size of brittle cracking region being composed of quasi-cleavage facets and interfacial cracks on the fracture surfaces was increased with the hydrogen charging time.