The microstructural characteristics of cast Mg-x Sn (x = 0.5, 1.0, 2.5 wt.% and 4.0 wt.%) alloys were systematically evaluated, as well as the electrochemical behavior and discharge properties in 3.5 wt.% NaCl solution. The micro-morphological results show that the grains are obviously refined and the Mg₂Sn phase distribution is uniform with the increase of Sn content. In the four tested alloys, the effect of Sn content on the corrosion resistance of the alloys was found to be bidirectional by using the loss-in-weight method and electrochemical measurements. Among them, Mg-2.5Sn exhibits higher corrosion resistance in 3.5 wt.% NaCl solution. The decrease of the self-corrosion rate of Mg-x Sn alloy is mainly due to the formation of a SnO₂ protective film, which inhibits the expansion of pitting corrosion. In addition, an appropriate amount of Mg₂Sn can weaken the self-corrosion behavior. Mg-1Sn exhibits the highest anode efficiency and discharge capacity of 56.11% and 1245.72 mAh·g⁻¹, respectively. Mg-0.5Sn shows the highest peak energy density, which is 1258.78 mWh·g⁻¹.The maximum average discharge voltage of Mg-2.5Sn is 1.461 V.

The effects of ultrasonic treatment on grain refinement and hydrogen removal in three kinds of magnesium alloys—Mg-3Ca, Mg-6Zn-1Ca, and AZ80 alloys—were investigated in this study. After ultrasonic treatment, the grains of the magnesium alloys were refined to varying degrees. The degassing effect was characterized by measuring the densities and hydrogen content of ingots. The results indicated that the application of ultrasonic treatment in these magnesium alloys was able to remove hydrogen and obviously refine the microstructure. In this experiment, both the measurement of the density of the ingots and the solid-state hydrogen measurement reflected the degree of degassing. The highest degassing efficiencies were 53.8%, 67.5%, and 34.9% for the Mg-3Ca, Mg-6Zn-1Ca, and AZ80 alloys, respectively. The lowest hydrogen content of the AZ80 alloy reached 8.2 cm³/100 g, and the corresponding tensile strengths were 174 Mpa, 79 Mpa, and 6.2%, which represented increases of 41.5%, 38.6%, and 87.9%, respectively. The cavitation effect and acoustic streaming effect with an appropriate ultrasonic treatment duration resulted in grain refinement, degassing, and the uniform dispersion of second phases. This can significantly improve mechanical properties and provide a basis for industrial production.

Mg–Sn–Ca alloys are promising candidates for Mg–air battery anodes. In this study, the influence of Sn/Ca mass ratio on the formation of the second phase, corrosion behavior and discharge performance of Mg-xSn-1Ca (x = 0.5, 1.0, 2.5, 4.0 wt%) alloys, has been investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and electrochemical characterizations. The results reveal that the CaMgSn phase forms in four Mg–xSn–1Ca alloys, the Mg₂Ca phase precipitates in low Sn/Ca mass ratio alloys (Mg-0.5Sn-1Ca and Mg–1Sn–1Ca), and the Mg₂Sn phase precipitates in the Mg-4Sn-1Ca alloy. Low Sn/Ca mass ratio alloys present better corrosion resistance than high Sn/Ca mass ratio alloys (Mg-2.5Sn-1Ca and Mg-4Sn-1Ca). The improvement in the corrosion resistance of the Mg₂Ca phase is more than that of the Mg₂Sn and CaMgSn phases. The highest average discharge voltage, anodic efficiency, power density, specific capacity, and specific energy of 1.188 V, 58.3%, 23.78 mW cm⁻², 1225.5 mA h g⁻¹, and 1389.8 mW h g⁻¹, respectively, are found for the Mg-0.5Sn-1Ca alloy at an Sn/Ca mass ratio of 0.34, at a current density of 20 mA cm⁻². This is attributed to better corrosion resistance and good electrochemical activity of the alloy. For the TX01 alloy, the current of discharge failure is calculated to be 93.6 mA.

The cooling characteristic curves in a heated ingot with a diameter of 100 mm quenched by a water jet were measured under different conditions. A two-dimensional calculation model was established to calculate the HTC of magnesium alloy ingot with water spray cooling. Data from cast-in thermocouples trail were input into the model and the HTCs were back-calculated for the water quench region. The HTCs were calculated under different alloy types and roughness conditions, and the relationship between the ingot surface temperature, roughness, and the HTC was established accordingly. The results show that the greater the thermal conductivity of the alloy, the greater the heat transfer coefficient (HTC). The HTCs of AZ80, AZ31, and ZK60 alloys increase successively. With the decrease in the surface temperature, the HTC in both the impingement zone and the free−falling zone shows a trend of a rapid increase at first, then slowly increasing to the maximum value, and finally, a rapid decrease, with the peak value appearing at about 400 K. Considering the influence of the ingot surface temperature and the surface roughness on the HTC, the mathematical relationships between them are established.

The secondary cooling of AZ80 during DC casting was investigated by measuring the temperature at a given position during steady state. The experiment was carried out under different parameters including the water flow rate density ($Q^{*}$) and initial temperature ($T_i$) of the impingement points. To theorize the heat transfer of the secondary cooling zone in practical DC casting, we designed a series of experimental equipment to simulate the secondary cooling with differing $T_i$ (between 473 and 673 K) and $Q^{*}$ (between 20 and 100 L min⁻¹ m⁻¹) based on the DC casting temperature-measurement experiment above. Detailed analysis was carried out of both the experimental results combined with $Q^{*}$. The empirical formulae of Rohsenow and Weckman were modified due to the need to divide the secondary cooling zone into an impingement zone and a free-falling zone. Finally, a verification of the model’s accuracy was conducted by comparing the results of the finite volume numerical simulation and the experiment, which revealed that the model exhibited extremely high accuracy.

The advanced lamellar microstructure significantly improves the toughness of Cu-bearing ultra-high strength steel by delamination toughening (yield strength: 1370 MPa, impact toughness at −40 °C: 60 J). The lamellar microstructure affects the microstructure evolution of heat-affected zone (HAZ), resulting in separate distributions of lath martensite and granular bainite in the complete austenitizing zone and the formation of cluster fresh martensite in the partial austenitizing zone. The grain refinement and decrease in dislocation density are predominant features, especially for the complete austenitizing zone, where the grain is refined to 4.33 μm, and dislocation density is decreased by 27%. With the degree of austenitizing increase, the dissolution of Cu-rich precipitates (CRPs) aggravates during welding. A small fraction of CRPs in the complete austenitizing zone implies the onset of reprecipitation of CRPs. The reason for softening in HAZ is attributed to a combined effect of granular bainite forming, dislocation density decreasing, and CRPs dissolving. After PWTH, large numbered reprecipitation of coherent CRPs occurs, contributing to the hardness recovery of HAZ. Meanwhile, due to the high density of dislocation of lamellar microstructure inherited by partial austenitizing zone, coarsening of coherent CRPs is easy to occur, and various incoherent structures are observed.