No abstract

In this work, the Al-10Si-2.5Cu-0.8Fe alloy was used as the base alloy to squeeze casting with different content Mg-10Al master alloy addition. The effects of microstructure and mechanical properties were investigated by XRD, OM, SEM, and tensile test analysis. The results show that with the increase of Mg addition, the morphology of eutectic Si in the alloy changes from strip to fiber and the size is obviously reduced. Al 8 Mg 3 FeSi 6 phase in the microstructure gradually grows, and the splitting effect on the matrix structure is increased. The tensile strength and elongation of the alloy increased first and then decreased with the increase of Mg content. When the Mg content is 1.38%, the tensile strength of the alloy reached a maximum of 289 MPa and the elongation is 2.24%. The hardness of the alloy gradually increases. When the Mg content is 2.51%, the hardness reaches 121.8 HV. The cleavage surface in the fracture becomes fine with the increase of Mg content, the number of dimples increases, and the fracture mode transitions from quasi-cleavage fracture to brittle fracture.

The microstructural evolution of S30432 heat-resistant steel during creep at 650 8C and its effect on the change in hardness was investigated. The change of hardness during creep of S30432 at 650 8C can be divided into three stages. These are related to the precipitation and coarsening of e-Cu and M 23 C 6 carbides, decrease in the number of twins and increase in grain size. The precipitation of e-Cu dominantly contributes to the significant hardening at stage I, and the coarsening of e-Cu is the key factor to decrease the hardness at stage II. At stage III, the hardness hardly changes since the microstructure of S30432 tends to be stable in the long-term creep range.

To provide insight into the mechanical behavior and microstructural evolution of bulk nanograined (NG) Ni-based alloys during annealing, the Ni-based alloy sheets with grain size about 50 nm was produced through severe cold-rolling at room temperature, and then the cold rolled (CRed) Ni-based alloys were annealed at different states. The evolution of the nanostructure of the CRed Ni-based alloy during annealing and corresponding change in mechanical properties was investigated. The results showed that the CRed Ni-based alloy exhibited prominent enhancement in the yield strength (YS), ultimate tensile strength (UTS), which increased respectively from 253 MPa to 1455 MPa, 684 MPa to 1557 MPa. Further increase of the YS and UTS were obtained in the annealed-CRed Ni-based alloy with dual-phase. The YS and UTS of the NG dual-phase Ni-based alloy was respectively 2013 MPa and 2061MPa, which was annealed at 700 °C for 1h. In terms of the microstructural evolution, lower density of defects on the grain boundary were observed and the nanograins can be maintained about 100 nm even when annealed for 30 h at 700 °C, which suggests high thermal stability at this temperature. Both the high thermal stability and strength are due to the formation of the γ′ precipitates and slight grain growth of the NG matrix.