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Effect of solution treatment on microstructure and mechanical properties of Al-12Si-4Cu-2Ni-0.8Mg-0.2Gd alloy was investigated. Results show the Si particles become stable and more intermetallic compounds dissolve in the matrix after solution treatment at 500 °C for 2 h followed by 540 °C for 3 h (T4). The skeleton-like Al3CuNi develops into two parts in the T4 alloy: one is Al3CuNi which has the framework shape; the other is intermetallics including the Al3CuNi (size: 5–10 µm) and AlSiCuNiGd phases (size: ≤5 µm) with complex structure. Adding 0.2% Gd can improve the mechanical properties of the alloys after two-step solution treatment (500 °C/2 h followed by 540 °C/3 h), the hardness of the alloy increases from 130.9 HV to 135.8 HV compared with the alloy with one-step solution treatment (500 °C/2 h), the engineering strength increases from 335.45 MPa to 352.03 MPa and the fracture engineering strain increases from 1.44% to 1.67%. [ABSTRACT FROM AUTHOR]

Fe–5Cr–1.5B–0.45C alloys exhibit excellent balance of hardness and toughness. The hard phase of boron carbide in the Fe–Cr–B–C alloy system of high-boron iron-based alloys plays a key role in various properties of the system. Therefore, in this study, several typical hard phase morphological and crystalline structures are analyzed in detail. Use of first-principle methods for calculating the thermodynamic and mechanical properties of the hard phase in Fe–5Cr–1.5B–0.45C alloys shows that the incorporation of alloying elements can further improve the properties of the alloys and the improvement of hardness can enhance the wear resistance properties. We investigate several typical hard phase morphological and crystalline structures in Fe–5Cr–1.5B–0.45C alloys, and calculate the thermodynamic and mechanical properties. It shows that the incorporation of alloying elements can reduce the enthalpies of formation of Fe2B compounds,and further improve the hardness and the wear resistance properties of the alloys. Image 1 • Typical morphology of the hard phase are lamellar, cluster, rod or lath and granular. • Thermodynamic and mechanical properties of various hard phases were calculated using of first-principle methods. • Orthorhombic structure Fe 3 (B, C) with the C or B element dissolved is comparatively formed easily. • Mo reduce the enthalpies of formation of Fe 2 B compounds, increase the hardness of Fe 2 B and Fe 3 C. • The incorporation of alloying elements can further improve its hardness and wear resistance. [ABSTRACT FROM AUTHOR]