| Summary: | In the present work, we studied the effects of transition metal elements on microstructure evolution and high-temperature mechanical properties via the preparation of new modified alloys with micro-additions of Cr, Ti, V, Zr, Mo, and Mn to address the poor high-temperature performance of Al–Si–Cu–Mg alloys for automotive engines. The results show that the addition of transition metal elements formed a variety of new intermetallic phases that were stable at high temperatures, such as (AlSi)<sub>3</sub>(TiVZr), (AlSi)<sub>3</sub>Ti, (AlSi)<sub>3</sub>(CrVTi), Al<sub>74</sub>Si<sub>6</sub>Mn<sub>4</sub>Cr<sub>2</sub>Fe, Al<sub>85</sub>Si<sub>5</sub>Mn<sub>2</sub>Mo<sub>2</sub>CrFe, Al<sub>0.78</sub>Fe<sub>4.8</sub>Mn<sub>0.27</sub>Mo<sub>4.</sub>15Si<sub>2</sub>, (AlSi)<sub>2</sub>(CrVTi)Mo, and Al<sub>13</sub>(MoCrVTi)<sub>4</sub>Si<sub>4</sub>, and these phases evidently improved the ultimate high-temperature tensile strength and yield strength. The ultimate tensile strength and yield strength of the modified alloy increased by 17.49% and 31.65% when the test temperature increased to 240 °C, respectively, and by 71.28% and 74.73% when the test temperature increased to 300 °C, respectively. The fundamental reason for this change is that the intermetallic phase hinders the expansion of cracks, which can exist stably at high temperatures. When a crack extends to the intermetallic phases, it will break along with the intermetallic phases or propagate along the morphological edge of the intermetallic phases.
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