Nodular Cast Iron (NCI, also known as ductile iron) is widely used in important components such as crankshafts for automotive engines and internal combustion engines, as well as storage and transportation containers for spent fuel in nuclear power plants, due to its good comprehensive mechanical properties such as strength, toughness, and wear resistance. The effect of temperature on the fracture behavior of NCI was investigated using compact tensile (CT) specimens at different temperatures. The results showed that the conditional fracture toughness parameter (K_Q) of the NCI specimens firstly increased and then decreased with decreasing temperature. The crack tip opening displacement δ_m shows a significant ductile–brittle transition behavior with the decreasing of temperature. δ_m remains constant in the upper plateau region but sharply decreases in the ductile–brittle region (−60 °C to −100 °C) and stabilizes at a smaller value in the lower plateau region. Multiscale fractographic analysis indicated that the fracture mechanism changed from ductile fracture (above −60 °C) to ductile–brittle mixed (−60 °C to −100 °C) and then to completely brittle fracture (below −100 °C). As the temperature decreased, the fracture characteristics changed from ductile dimples to dimple and cleavage mixed and then to brittle cleavage.

The long-period stacking ordered (LPSO) structure, functioning as a strengthening phase in magnesium alloys, plays a pivotal role in compensating for inherent performance limitations. In this study, an as-cast Mg-Gd-Ni-Y alloy, including the LPSO phase, was initially obtained through an ingot metallurgy process. Subsequently, the alloy underwent distinct thermal treatments: annealing at 500 °C for 10 h, and extrusion using an extrusion ratio of 10 at a speed of 5 mm/s. Comparative analysis of the microstructure and corrosion characteristics was performed across these three alloy states. Comprising primarily of α-Mg, LPSO phase, and eutectic structures (ES), the alloy exhibited distinctive microstructural features. Immersion experiments conducted in a 3.5% NaCl solution revealed that the as-cast alloy displayed the highest dissolution rate at various temperatures, from room temperature, to 50 °C, and 70 °C. Following annealing, a reduction in the second phase content within the alloy significantly contributed to the observed decrease in its dissolution rate. Extrusion processes resulted in a denser network structure within the microarchitecture, to some extent impeding the spread of corrosion to some extent. By emloying scanning Kelvin probe force microscopy (SKPFM) and micro-electrochemical testing, it was discerned that predominantly the electrochemical system involving α-Mg and the second phases predominantly dictated the heightened dissolution rate of the alloy. This study presents valuable insights into understanding the dissolution mechanisms and potential strategies for controlling the dissolution performance of magnesium alloys containing the LPSO phase.