Abstract
The effects of rare earth yttrium (Y) additions and the heat treatment process on the microstructure and mechanical properties of as-cast ADC12 aluminum alloy have been investigated. The results showed that the primary Si crystals were significantly refined from long axis to fibrous or granular when the Y content was 0.2 wt%. Compared to the matrix, the mean area and aspect ratio were decreased by 92% and 75%, respectively. Moreover, the Si and Fe-rich phases were spheroidized and refined with a small average size during the solid solution. It was also noted that the copper-rich phases were dissolved into the matrix. Correspondingly, it was found that after metamorphic and heat treatment the ultimate tensile strength (UTS), elongation, and, hardness increased by 81.9%, 69.7%, and 74.8%, respectively, compared to the matrix. The improved mechanical properties can primarily be attributed to the optimization of the microstructure and the refinement of various phases.
Highlights
Due to its excellent castability and mechanical properties, ADC12 alloy has attracted the attention of the automotive and aviation industry [1]
The coarse or lamellar shape of eutectic Si and long needle-like iron-rich phases exists in the alloy and reduces the mechanical properties and elongation [2]
Some reports indicate that the distribution of eutectic silicon, or other phases in the matrix, were improved effectively by adding rare earth [3] or alkali metal [4] to the melt
Summary
Due to its excellent castability and mechanical properties, ADC12 alloy has attracted the attention of the automotive and aviation industry [1]. The coarse or lamellar shape of eutectic Si and long needle-like iron-rich phases exists in the alloy and reduces the mechanical properties and elongation [2]. Li. et al [5] studied the effect of rare earth Y on the hot-tearing behavior of Al-Cu alloy. They revealed that Y has a distinct grain refining effect on the alloy, which decreased the liquidus temperature and shortened the crystallization range. Zhang et al [6] found that the grains of an Al-Zn-Mg-Cu-Zr alloy were significantly refined by adding a mix of rare earth elements (Gd and Y). Several researchers [7,8] demonstrated that the rare earth Y has an excellent refining effect on Si and iron-rich phases while reducing alloy defects
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