Development and characterization of low-silicon cast aluminum alloys for thermal dissipation

Two low-silicon quaternary aluminum alloys, Al-(0.5-1.5)Mg-1Fe-0.5Si and Al-(1.0-1.5)Si-1Fe-1Zn, are investigated for their potential to combine a high thermal conductivity with good castability and anodizability. By comparing to the physical and casting properties of the commercial ADC12 alloy, the developed alloys show 170-190% of thermal conductivities (160-180 W/m K), a similar medium-thick-wall fluidity, 60-85% of thin-wall fluidity, 100-130% of hot tearing susceptibility (HTS), and a comparable ultimate tensile strength. As Mg and Si, the major alloying elements, increase, the thermal conductivity decreases and the strength increases. The thin-wall fluidity and the HTS are both inversely proportional to the Mg content and directly proportional to the Si content. These opposite trends within the two alloy systems arise mainly from differences in the Al dendrite coherency and first intermetallic crystallization points, and in the crystallization behavior of β-AlFeSi phase. The lower viscosity and lower surface energy of the Al-(0.5-1.5)Mg-1Fe-0.5Si and Al-(1.0-1.5)Si-1Fe-1Zn alloys, respectively enhance their fluidity in thicker and thinner sections. A large fluidity sensitivity to the channel diameter of the aluminum alloys developed here is attributed to their higher melting points, lower latent heats, and higher formation tendency of oxide films and inclusions.