RESUMO
AS41 magnesium alloy possesses outstanding performance features such as light weight, high strength to toughness ratio and excellent heat resistance due to the addition of Si element, while traditional casting methods are prone to inducing large grain size and coarse Mg2Si phase. In this study, we first reported utilizing the selective laser melting (SLM) technique, fabricating AS41 samples and exploring the effect of laser energy densities on the metallurgical quality by characterizing and investigating the microstructure and mechanical properties. Results showed that the optimal laser energy density range was 60 to 100 J/mm3. Average grain size of only 2.9 µm was obtained with weak texture strength of 1.65 in {0001} orientation. Meanwhile, many dispersed secondary ß-Mg17Al12 and Mg2Si phases were distributed inside the α-Mg matrix. It was confirmed that the SLM process introduced more grain recrystallization, inducing giant high-angle grain boundaries (HAGBs) and hindering the movement of dislocations, therefore forming dislocation strengthening while achieving grain refinement strengthening. Finally, three times the ultimate tensile strength of 313.7 MPa and higher microhardness of 96.4 HV than those of the as-cast state were obtained, verifying that the combined effect of grain refinement, solid solution strengthening and precipitation strengthening was responsible for the increased strength. This work provides new insight and a new approach to preparing AS41 magnesium alloy.
RESUMO
A novel efficient reduction route was developed for preparing porous pellets to enhance mass transfer during magnesium production, which can improve the reactivity of pellet reaction to improve the reduction efficiency. A porous pellet precursor was prepared at 150 MPa using NH4HCO3 as a pore-forming agent, and the reaction characteristics of the pellets with 0, 5%, 10%, 20%, and 30% pore-forming agents were measured under a high vacuum of approximately 10 Pa heat-treated from 100 °C to 1400 °C. The results showed that the instantaneous maximum reduction rate first increased and then decreased with the increase in pore-forming agents. When the reduction conversion was 80%, the reduction efficiency of pellets with 5% pore-forming agent was 36% greater than that without pore-forming agent pellets. When the reduction conversion was 90%, the reduction efficiency of pellets with 5% pore-forming agent was 29% greater than that without pore-forming agent pellets. The results indicate that the diffusion rate of magnesium vapor in pellets is significantly increased; the time of chemical reaction reaching equilibrium is shortened; the chemical reaction rate and the magnesium production efficiency are increased by adding a proper ratio of NH4HCO3 compared to that obtained without NH4HCO3 at the identical reduction temperature.
RESUMO
1Cr13MoS is a kind of material with excellent corrosion resistance and good mechanical properties. Meanwhile, it also has good self-lubricating properties due to the presence of molybdenum disulfide phase inside the material and can be used as friction pair material in the pump. In this paper, the hardness, microstructure, distribution of the self-lubricating phase, friction and wear properties of 1Cr13MoS after heat treatment were studied. After quenching at 1000 °C and tempering at 520 °C, the hardness of 1Cr13MoS prepared by pyrometallurgy is higher than that of HB 350. The tempering sorbite structure is evenly distributed, and the self-lubricating phase MoS2 is discretely distributed on the substrate with the average size is about 6 µm, which leads to good friction and wear properties. It is worth noting that the 1Cr13MoS is actually operated as friction pair material on the water pump and has a significant wear improvement effect compared to the conventional 12% chrome steel series.
