Effects of Pulsed Magnetic Field Melt Treatment on Grain Refinement of Al-Si-Mg-Cu-Ni Alloy Direct-Chill Casting Billet

Abstract

Al-Si-Mg-Cu-Ni alloy is widely used in the manufacture of high-performance car engine parts. Coarse, dendritic α-Al and large primary Si are common in Al-Si-Mg-Cu-Ni alloy DC casting billet, which is harmful to the performance of the final product. In this paper, a pulsed magnetic field melt treatment technique was applied to the melt in the launder of a DC casting platform to modify the α-Al and primary Si in the billet. A transient numerical model was established to analyze the electromagnetic field, flow field and temperature field in the melt during the pulsed magnetic field treatment. The effect of the magnetic energy on the clusters in the melt was analyzed. We found that during the pulsed magnetic field melt treatment, the number of clusters close to the critical size was increased due to the cluster formation work being reduced by the magnetic energy, which facilitated nucleation and refined the solidification structure. Furthermore, the flow velocity increased, and temperature homogenized in the melt during the pulsed magnetic field melt treatment, which benefitted the clusters close to the critical size distributed and maintained in the melt uniformly. The experimental results show that the α-Al and primary Si were small and homogeneous following the pulsed magnetic field melt treatment. The size of α-Al and primary Si was reduced by 25.6–44.4% and 32.2–54.1%, respectively, in the billet center compared to the conventional process.

Effects of PMMT on microstructure and macrosegregation of large-sized 6061 alloy billet

“…According to the classical nucleation theory, there are many clusters with various sizes in the melt. During the PMMT, the energy of the pulsed magnetic field permeates into the melt, the cluster formation process was changed significantly in the melt due to the formation work reduced by the energy of the pulsed magnetic field, which lead to the number of the larger clusters increasing in the melt [21]. In the solidification stage, the change in Gibbs free energy of nucleation can be expressed as: Where normalΔGv is the driving force, it is constant when the undercooling is constant; r is the critical radius; σ is the specific surface free energy.…”

“…Based on our previous research results [20][21][22], a whole new PMMT process was successfully applied to the commercial 6061 alloy DC-casting process to refine the solidification structure of the billet with a diameter of 430 mm. The results show the great potential of the PMMT to be used in larger-sized aluminium alloy DC-casting billets solidification structure refinement.…”

Effect of Wide-Spectrum Pulsed Magnetic Field on Solidification Structure of Pure Al at Constant Flow Velocity

“…Bai Qingwei et al [8] studied the effect of a pulsed electromagnetic field on the solidification structure of 7A04 aluminium alloy, and the results showed that a pulsed magnetic field can effectively produce spherical grains and a uniform microstructure in the alloy. Bao et al [9] applied pulsed magnetic field (PMF) technology to an Al-Si-Mg-Cu-Ni alloy melt in the direct chill casting process, and found that the size of α-Al and primary Si will be reduced after PMF treatment, while the distribution will be more uniform. Gong Yongyong et al [10] discovered that the application of pulsed magnetic oscillation (PMO) during the nucleation stage and the first half of the nucleation growth can refine the structural solidification of the metal, with crystal nuclei originating from the mould wall and the liquid surface of the melt.…”

Microstructure Evolution in a 6082 Alloy under Pulsed Magnetic Field Melt Treatment

“…When the 0.27 wt.% grain refiner was combined with the PMMT, it could achieve the smallest α-Al grains size, which is 116.10 μm, 111.40 μm and 88.26 μm in the billet centre, 1/2 R and edge, respectively.It is well known that the increase of the nucleation rate is the main reason for the solidification structure being refined. When the melt was treated by the pulsed magnetic field, the energy of the pulsed magnetic field permeated into the melt, leading to the number of the larger clusters being increased in the melt[13]. During the solidification, larger clusters transformed into nuclei in a short time, leading to an increase in the nucleation rate[14].…”