Abstract
In recent years, many efforts have been devoted to the development of innovative Al-based casting alloys with improved high temperature strength. Research is often oriented to the investigation of the effects of minor element additions to widely diffused casting alloys. The present study focuses on Al-7Si-0.4Mg (A356) alloy with small additions of Er and Zr. Following previous scientific works on the optimization of heat treatment and on tensile strength, creep tests were carried out at 300 °C under applied stress of 30 MPa, a reference condition for creep characterization of innovative high-temperature Al alloys. The alloys containing both Er and Zr displayed a lower minimum creep strain rate and a longer time to rupture. Fractographic and microstructural analyses on crept and aged specimens were performed to understand the role played by eutectic silicon, by the coarse intermetallics and by α-Al matrix ductility. The creep behavior in tension of the three alloys has been discussed by comparing them to tension and compression creep curves available in the literature for Al-7Si-0.4Mg improved by minor elemental additions.
Highlights
Alloy with Er and Zr Additions.A356 (Al-7Si-0.4Mg) is a casting alloy widely applied in automotive and aeronautical fields, as referred by Mishra et al [1] and Jeong et al [2], among others
The casting alloys are characterized by the dendritic grain size of 1462 ± 350 μm for A356 alloy, 1157 ± 186 μm for E3 alloy and 383 ± 98 μm for the Zr-containing alloy
The creep curves of the three alloys were compared to known literature creep curves of the A356 alloy and of some alloys modified by the addition of elements, tested under the same temperature and stress, but in tension or compression loading and with different initial temper condition [39,40,51,52]
Summary
Alloy with Er and Zr Additions.A356 (Al-7Si-0.4Mg) is a casting alloy widely applied in automotive and aeronautical fields, as referred by Mishra et al [1] and Jeong et al [2], among others. An artificial aging at temperatures 155–200 ◦ C follows [3], during which the β-Mg2Si precipitation sequence evolves to what observed in wrought Al-Mg-Si alloys, where the Si or U2-Mg-Al-Si phase can be observed substituting β” in alloys with high. The high temperature behavior of the Al-Si-Mg age-hardenable casting alloys is strictly connected to overaging processes, related to the instability and fast growth of strengthening particles of the abovementioned precipitation sequence. Several minor elemental additions have been proposed during the years to improve mechanical properties at high temperature and/or mechanical stability of the A356 alloy [2,7,8,9,10,11,12,13]. During the years, modified A356 alloys with minor additions of Mo [8], Metals 2021, 11, 879. https://
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