Effects of Cu content on the microstructure, mechanical property, and hot tearing susceptibility of die casting hypereut
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effects of Cu content on the microstructure, mechanical property, and hot tearing susceptibility of die casting Al–22Si–0.4Mg alloy have been investigated. Different Cu contents (1.5, 2.5, 3.5, 4.5 wt%) were added in Al–22Si–0.4Mg alloy. In the as-cast microstructure, the amount, volume fraction, and average size of Al2Cu phase increase with more Cu addition. The morphology of grain boundary white Al2Cu phase turns from particle to lump. The UTS (ultimate tensile strength) of Al–22Si–xCu–0.4Mg alloy improves with Cu added, which is mainly caused by the strengthening effect of intergranular Al2Cu. The hot tearing susceptibility apparently rises with Cu content increased, which is due to longer quaternary eutectic reaction time, larger amount of residual intergranular Cu-rich liquid film spreading out over a-Al grain boundary, and higher quaternary eutectic reaction temperature. Considering both the mechanical property and hot tearing susceptibility, optimal Cu content for die casting Al–22Si–0.4Mg alloy found in this paper is 2.5 wt%.
I. INTRODUCTION
Hypereutectic Al–Si alloys have been widely used in aerospace, automobile, and general engineering industries due to their excellent mechanical properties such as light weight, favorable corrosion resistance, high wear resistance, excellent thermal conductivity, and low thermal expansion coefficient.1–5 Nowadays, more attention has been paid to hypereutectic Al–Si alloys, as they can improve fuel efficiency and reduce emission when served as engine block and piston alloy in automobile industry.6,7 With the increasing of Si content, better friction resistance, lower density, and lower heat expansion coefficient can be achieved in hypereutectic Al–Si alloy. More fuel saving and less automobile exhaust emission will be attained if more low-density hypereutectic Al–Si alloy is used to make automobile power system components. Moreover, high Si content hypereutectic Al–Si alloy is favorable to casting processing owning to its good fluidity, which is primarily due to the high latent heat of the crystallization of Si. Therefore, increasing Si content has become an imperative and feasible research direction to develop next generation hypereutectic Al–Si alloy. Even though primary and eutectic Si can enhance the wear resistance of Al–Si alloys, the polygonal primary Contributing Editor: Jürgen Eckert a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2016.388
Si block and acicular eutectic Si will segregate the matrix severely and thus undermines the mechanical properties of the alloy. To make it worse, the modification effect of Si will be impaired when Si content is higher than 26 wt%. In addition, large primary Si lump forms easily in conventional cast process. On the other hand, with the addition of Si, it is increasingly difficult to shape automobile power system components with complex shape by conventional cast process. To shape complex automobile components with refining and dispersing primary Si, a multitude of novel methods were dev
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