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Creep rupture behavior of dissimilar weldments between FB2 and 30Cr1Mo1V heat-resistant steel by multipass welding at 783 K (510°C) under different stresses (260 to 420 MPa) was researched. The fitted creep rupture exponent is 14.53, and the 10,000 h extrapolating strength values predicted by the power law and Larson-Miller parameter show good agreement with experimental data. The samples exhibit a ductile fracture character and fracture in the weld fusion zone, which has a highly heterogeneous microstructure and grains with different morphologies and sizes and an obvious softening. There exist a decrease in the dislocation and precipitate density and an increase in the subgrain size in the weld metal after creep. The rupture is a transgranular fracture characterized by dimples as a result of microvoid coalescence. Laves phases along with copper-rich precipitates are observed in the vicinity of fracture surface, which creates a stress concentration that can cause transgranular fracture initiation.

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The evolution of microsturcture and mechanical properties of ZYK530 Magnesium alloy during extrusion and die forging compound forming process were studied and analyzed. The results show that the as-cast ZYK530 alloy mainly consists of a-Mg matrix and I-Mg3Zn6Y and a small amount of W-Mg3Y2Zn3 and Mg2Zn3 phases. During extrusion to die forging forming, the grain size of as-cast ZYK530 Magnesium alloy is refined and uniform under the action of three-dimensional compressive stress and high temperature deformation. The I-Mg3Zn6Y phase of ZYK530 magnesium alloy decrease relatively, while the distribution of W-Mg3Y2Zn3 is more obvious, a small amount of Z-Mg12ZnY and Mg-Zn phases and undetermined phases can be observed in the matrix. Tensile test results show that the tensile strength, yield strength and elongation of extruded preformed specimens are increase by 32.6%, 18% and 18% respectively compared with as-cast specimens. The mechanical properties of final forged specimens are improved by 9%, 38.6% and 23% respectively compared with those of extruded preformed specimens. The fracture mechanism changes form as-cast cleavage fracture to mixed fracture mechanism of toughness and brittleness.