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Abstract
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)3(TiVZr), (AlSi)3Ti, (AlSi)3(CrVTi), Al74Si6Mn4Cr2Fe, Al85Si5Mn2Mo2CrFe, Al0.78Fe4.8Mn0.27Mo4.15Si2, (AlSi)2(CrVTi)Mo, and Al13(MoCrVTi)4Si4, 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.
Highlights
Al–Si casting alloys are widely used in manufacturing automotive engine cylinder heads due to their advantages of being lightweight, good casting performance, and excellent comprehensive mechanical properties [1]; with the contradictory development of high load stress and thin-walled structure of the high-performance engine, the requirements for the balance of strength and toughness at room temperature as well as the high-temperature performance of aluminum alloy cylinder heads and engine blocks are becoming stricter
The basic intermetallic phases consisted of α-Al dendrites (1#), Al–Si eutectic (2#), Al2Cu with granular and blocky-shapes (3#,4#), and Q-Al5Cu2Mg8Si6 (5#)
It was found that V, Zr, and Ti atoms mainly exist in the rich TiVZr phase, whereas Cr, Mn, and Mo atoms are mainly distributed in the rich CrVTi phase, rich TiVMo phase, and rich MoMnFe phase
Summary
Al–Si casting alloys are widely used in manufacturing automotive engine cylinder heads due to their advantages of being lightweight, good casting performance, and excellent comprehensive mechanical properties [1]; with the contradictory development of high load stress and thin-walled structure of the high-performance engine, the requirements for the balance of strength and toughness at room temperature as well as the high-temperature performance of aluminum alloy cylinder heads and engine blocks are becoming stricter To meet this market demand, researchers began to study how to achieve better values of both strength and ductility at room temperature and improve the high-temperature performance of Al–Si casting alloys. The elements that meet the above conditions are Cr, Ti, V, Zr, Mo, Mn, and other transition metal elements
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