Effects of Ni and Cu Addition on Tensile Properties and Thermal Conductivity of High Pressure Die-cast Al-6Si Alloys

Abstract

In this study, the effects of nickel and copper on the mechanical and thermal properties of Al-Si alloys were investigated, for different alloy compositions. Thermodynamic calculations were carried out to predict the alloys’ solidification behavior (solidification temperature, solid fraction and physical properties (density, thermal conductivity, elastic modulus, bulk modulus)). The aluminum alloys were produced by high pressure die-casting process with a 125 ton die-casting machine. Microstructures in the Al-Si-Ni alloys were characterized by optical microscopy and scanning electron microscopy. The mechanical properties were evaluated by tensile tests. Thermal conductivity was measured using a laser flash method. The addition of Ni and Cu improved the mechanical properties of the alloys by different strengthening mechanisms. Solution strengthening was the more effective method of improving mechanical properties, compared with strengthening by intermetallic compounds. The addition of an appropriate concentration of soluble alloying elements consistently improved alloy strength. However, addition of alloying elements decreased the thermal conductivity of the primary alpha aluminum phase. EDS analysis confirmed that soluble alloying elements like Cu not only can form intermetallic compounds, but can also change other kinds of compounds. Accordingly, careful consideration should be given to the chemical composition of soluble/insoluble alloying elements when attempting to improve mechanical properties and thermal conductivity at the same time.

Research Progress on Thermal Conductivity of High-Pressure Die-Cast Aluminum Alloys

“…In Figure 8b, Al 2 Cu particles in the alloy improved the hardness to 75 HV and maintained thermal conductivity within 140~150 W m −1 K −1 for the die-cast alloy. Furthermore, except Zn, Jae-Cheol Jang et al [76] strongly increased the mechanical properties and the thermal conductivities of the three samples were negatively correlated with the fraction of these secondary phases. Cr and Ti were also added into the Al-7Si-3Mg die-cast alloy [81].…”

“…In Figure 8b, Al2Cu particles in the alloy improved the hardness to 75 HV and maintained thermal conductivity within 140~150 W m −1 K −1 for the die-cast alloy. Furthermore, except Zn, Jae-Cheol Jang et al [76] added elements Ni and Cu with different contents into Al-6Si die-cast alloys. The strength increased by over 300 MPa mainly due to the solid solution strengthening from element Cu.…”

Influence of Si, Cu, B, and Trace Alloying Elements on the Conductivity of the Al-Si-Cu Alloy

“…The conductivity of Al-Si alloys has been extensively researched in the last few decades [13][14][15][16][17][18][19]. Wen et al [13] found that high conductivity in Al-7Si alloys was produced through the optimization of the eutectic Si: i.e., by changing the size and distribution of the eutectic Si phase by a transformation from coarse plates to fine short slabs or coral-shaped particles.…”

“…Belov et al [18] found a lower conductivity for a higher Cu content attributed to more lattice distortion. Jiang et al [19] found that the soluble alloying elements like Cu decreased conductivity of the primary alpha Al phase and that these could form intermetallic compounds and could also change other kinds of compounds. These studies have indicated that the conductivity of Al-Si alloys depends on the major alloying additions.…”