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The evolution of three major heat-resistant phases (δ-Al3CuNi, γ-Al7Cu4Ni, T-Al9FeNi) and its strengthening effects at high temperature in Al–Si piston alloys with various Fe/Ni ratios were studied using field emission scanning electron microscope (FE-SEM), electron probe microanalysis (EPMA), and X-ray diffraction (XRD). With the increase of Fe/Ni ratios, the heat-resistant phases begin to evolve in category, morphology, and distribution. The results show that a suitable Fe/Ni ratio will cause the T-Al9FeNi phase to appear and form a closed or semi-closed network with δ-Al3CuNi and γ-Al7Cu4Ni phases instead of the originally isolated heat-resistant phases. As a result, the ultimate tensile strength of the optimized alloy reached 106 MPa with a Fe/Ni ratio of 0.23, which was 23.3% higher than that of base alloy at 350 °C, which is attributed to the fact that a closed or semi-closed network microstructure is advantageous to the bearing of mechanical loads. This work may provide useful ideas for the development of high temperature resistant piston alloys. [ABSTRACT FROM AUTHOR]

Highlights: [•] Morphology evolution of ZrAlSi phase in Al–18Si–xZr alloys was detected. [•] The morphology transforms from flake-like to block-like with Zr content. [•] Effect of different morphological ZrAlSi on the properties of an A–Si piston alloy was studied. [•] Blocky ZrAlSi phase is good for the elevated-temperature tensile strength. [Copyright &y& Elsevier]

Developing high-strength Al-based alloys that can operate at 250 °C and above remains a challenge. In this study, a heat-resistant and high-strength (4TiC + 5AlN)/Al–Fe–Mn composite is designed using the liquid–solid reaction and hot extrusion. The strengthening phases, including sub-micron TiC, micron Al 3 (Fe, Mn), nano-sized AlN, and nano-sized Al 3 (Fe, Mn), in which the in–situ AlN particles are distributed in the matrix as networks, exhibit an attractive strengthening effect. Based on the results of electron backscatter diffraction, the extruded (4TiC + 5AlN)/Al–Fe–Mn composite prefers to form fiber texture in the longitudinal and cross-section:<111> Al //ED. And the average grain size of (4TiC + 5AlN)/Al–0.3Fe–0.1Mn composite is 0.69 µm. The ultimate tensile strength of the (4TiC + 5AlN)/Al–Fe–Mn composite is as high as 215 MPa at 350 °C. And the high-temperature elongation of the (4TiC + 5AlN)/Al–Fe–Mn composite is maintained while increasing the high-temperature strength. The improved performance of the (4TiC + 5AlN)/All–Fe–Mn is attributed to the synergistic effect of the multi-scale Al 3 (Fe, Mn) phases and particles. Furthermore, the formed micrometer Al 3 (Fe, Mn) phases are used to regulate the distribution of the TiC and AlN particles. The nano-Al 3 (Fe, Mn) dispersoids that precipitated during the homogenization can enhance the high-temperature deformation resistance of the matrix. In particular, the Fe and Mn atoms tend to aggregate at the TiC/Al interface, effectively modifying the interfaces between ex-situ TiC particles and the Al matrix. The modified interfaces of TiC/Al are beneficial to load transfer strengthening. The strengthening mechanisms of the (4TiC + 5AlN)/Al–Fe–Mn composite have been analyzed in detail, and the main strength–increasing mechanisms are calculated from the microstructural data. This work may provide an important approach to preparing heat-resistant Al matrix composites with strength-ductility matching. • The UTS of (4TiC + 5AlN)/Al–0.3Fe–0.1Mn composite at 350 °C can reach 215 MPa and maintain a certain degree of ductility. • The synergistic effect of particles and multi-scale Fe/Mn enrichment is responsible for the enhanced UTS of A 3 composite. • The main strengthening mechanisms of A 3 composite were calculated through the microstructural data. [ABSTRACT FROM AUTHOR]

In this paper, a new kind of AlTiC–B master alloy, containing large amounts of nano‒sized TiC particles, has been applied in 7050 alloy. The influence of master alloy addition on the casting microstructures, extrusion behaviors and mechanical properties of 7050 has been investigated. It is found that 0.5 wt% addition of AlTiC–B master alloy exhibits the most attractive performance, resulting in much finer matrix grains and less casting defects. After hot extrusion, typical <100> and <111> fiber textures co‒exist in the microstructure of original 7050 alloy, whereas the alloys with AlTiC–B inoculation possess a higher intensity of <111> fiber texture. Besides, the inoculated alloys show better anti–recrystallization performance and larger local misorientation. It has been confirmed that a proper addition of AlTiC–B master alloy is beneficial for the mechanical properties of extruded 7050, which may be due to its refining effect on α–Al grains and its improvement for the precipitation of L1 2 –ZrAl 3. The Brinell hardness, ultimate tensile strength, yield strength and elongation of 7050 alloy with 0.5 wt% addition of AlTiC–B addition are 174 HBW, 665 MPa, 724 MPa and 9.8%, respectively. This work provides a promising prospect of AlTiC–B master alloy for applying in 7050 alloy in industries. • Research highlights: • A new AlTiC–B master alloy with B doped nano‒sized TiC particles was applied on 7050 alloy. • Improvement of casting quality and grain refining can be achieved with AlTiC–B inoculation. • Texture intensity and recrystallization fraction of as‒extruded 7050 vary with AlTiC–B addition. • Mechanical properties can be significantly improved. [ABSTRACT FROM AUTHOR]