45钢固体粉末法稀土、硼、铬、铝共渗工艺研究

研究了RE_Mg合金对固体粉末法硼、铬、铝共渗层成分、组织和性能的影响 .发现随着RE_Mg合金加入量的增加 ,渗层中Al2 O3的量不断增多 ,当RE_Mg合金加入量为 5 %时 ,渗层中出现连续致密分布的Al2 O3黑区组织 。

Dynamic recrystallization mechanisms during hot compression of Mg-Gd-Y-Nd-Zr alloy

Hot compression tests were conducted on a homogenized Mg-7Gd-4Y-1Nd-0.5Zr alloy at 450 ℃ and a strain rate of 2 s-1. Dynamic recrystallization （DRX） mechanisms were investigated by optical microscope （OM）, scanning electron microscope （SEM） and transmission electron microscope （TEM） systematically. The crystallographic orientation information is obtained through electron back-scattering diffraction （EBSD）. The result shows that the flow stress firstly reaches a peak rapidly followed by declining to a valley, and then increases gradually again when the alloy is compressed to a strain of-1.88. DRX related to {10]2} tensile twins is extensively observed at small strains, resulting in an evident grain refinement. DRX grains first nucleate along the edges of twin boundaries with about 30~ （0001） off the twin parents. While at large strains, conventional continuous DRX （CDRX） is frequently identified by the formation of small DRX grains along the original grain boundaries and the continuously increasing misorientation from the centre of large original grains to the grain boundaries. Evidence of particle-stimulated nucleation （PSN） is also observed in the present alloy.

Effects of minor Ca on as-cast microstructures and mechanical properties of Mg-3Ce-1.2Mn-0.9Sc and Mg-4Y-1.2Mn-0.9Sc alloys

The effects of the addition of 0.6%Ca（mass fraction） on the as-cast microstructure and mechanical properties of the Mg-3Ce-1.2Mn-0.9Sc and Mg-4Y-1.2Mn-0.9Sc magnesium alloys were investigated and compared by optical microscopy and scanning electron microscopy,differential scanning calorimetry analysis,and tensile and creep tests.The results indicate that the addition of 0.6%Ca to the Mg-3Ce-1.2Mn-0.9Sc and Mg-4Y-1.2Mn-0.9Sc alloys can refine the grains of the two alloys.At the same time,the addition of 0.6%Ca to the Mg-3Ce-1.2Mn-0.9Sc and Mg-4Y-1.2Mn-0.9Sc alloys can effectively improve the tensile properties of the two alloys.In addition,the addition of 0.6%Ca can also improve the creep properties of the Mg-3Ce-1.2Mn-0.9Sc alloy but is not beneficial to the creep properties of the Mg-4Y-1.2Mn-0.9Sc alloy.The different effects of minor Ca on the creep properties of the Mg-3Ce-1.2Mn-0.9Sc and Mg-4Y-1.2Mn-0.9Sc alloys are possibly related to the difference in the solid solubilities of Ce and Y in Mg.

Influence of heat treatment on microstructures and mechanical properties of gravity cast Mg-4.2Zn-1.5RE-0.7Zr magnesium alloy

The microstructures and mechanical properties of Mg-4.2Zn-1.5RE-0.7Zr alloy were investigated under different heat treatment conditions. The as-cast alloy consisted ofα-Mg phase, T-phase and Mg51Zn20 phase. After aging treatment （single-step （325 °C, 10 h） and two-step （325 °C, 4 h）＋（175 °C, 14 h））, neither T-phase nor Mg51Zn20 phase dissolved into the matrix and the coarsening ofα-Mg phase was not significant. When peak-aged at 325 °C for 10 h, dense short rod-likeβ′1 phase precipitated in the matrix. Further ageing at 325 °C led to coarsening ofβ′1 phase and a decrease in number density. Alloy aged at 325 °C for 10 h achieved the highest yield strength （YS） and ultimate tensile strength （UTS） of 153.9 MPa and 247.0 MPa, which were increased by 48 MPa and 23 MPa from as-cast condition, respectively. While the elongation slightly decreased to 15.6%. Comparatively, the YS and UTS of alloy two-step aged by （325 °C, 4 h）＋（175 °C, 14 h） showed little difference from those of single-step aged alloy, but with a lower elongation of 13.4%. In addition, the fracture surfaces of Mg-4.2Zn-1.5RE-0.7Zr alloy under different thermal conditions were mainly characterized by quasi-cleavage feature, but with differences in the details.

Structural and corrosion characterization of biodegradable Mg-RE (RE=Gd, Y, Nd) alloys

Binary Mg-Gd （up to 5% Gd in mass fraction）, Mg-Nd （up to 9% Nd in mass fraction） and ternary Mg-Gd-Y （up to 5% Gd, 1% Y） alloys with precisely determined contents of cathodic impurities （Fe, Ni, Cu, Co） were studied. The alloys were studied in the as-cast state （cooling rate of 500 K/min） and after solution heat treatment （T4）. Structures were investigated by optical and scanning electron microscopy, energy dispersive spectrometry, X-ray diffraction and glow discharge spectrometry. Structural investigation was completed by Vickers hardness measurements. Corrosion behavior in the simulated physiological solution （9 g/L NaCl） was assessed by immersion tests and potentiodynamic measurements. It was found that the structures of the as-cast alloys were dominated by fine a-Mg dendrites and eutectic Mg-RE phases. The dendrites exhibited RE-concentration gradients which were most pronounced in the Mg-Gd alloys. For this reason, the T4 heat treatment of the Mg-Gd alloy led to the formation of a new cuboidal Mg5Gd phase. The corrosion resistance was significantly improved by Gd. The effect of Nd was weak and the addition of Y to Mg-Gd alloys had harmful effect on the corrosion resistance. The T4 heat treatment strongly accelerated the corrosion of Mg-Gd alloys. Its effect on the corrosion of Mg-Nd alloys was not significant. The observed corrosion behavior of the alloys was discussed in relation to their structural states and contents of cathodic impurities.